Mountain streams

I TA L I A N H A B I TAT S

5

I TA L I A N H A B I TAT S

M I N I S T E R O D E L L’ A M B I E N T E E D E L L A T U T E L A D E L T E R R I T O R I O

M U S E O F R I U L A N O D I S T O R I A N AT U R A L E · C O M U N E D I U D I N E

Mountain streamsLife in running waters

Italian habitatsItalian Ministry of the Environment and Territory Protection / Ministero dell’Ambiente e della Tutela del TerritorioFriuli Museum of Natural History / Museo Friulano di Storia Naturale · Comune di Udine

Scientific coordinatorsAlessandro Minelli · Sandro Ruffo · Fabio Stoch

Editorial commiteeAldo Cosentino · Alessandro La Posta · Carlo Morandini · Giuseppe Muscio

“Mountain streams · Life in running waters”edited by Fabio Stoch

TextsMarco Cantonati · Valeria Lencioni · Bruno Maiolini · Mauro Marchetti · Karin Ortler · Mario Panizza ·Sergio Paradisi · Margherita Solari · Fabio Stoch

English translationElena Calandruccio · Gabriel Walton

IllustrationsRoberto Zanella

Graphic designFurio Colman

PhotographsArchive Museo Friulano di Storia Naturale (Ettore Tomasi) 47/1, 47/3, 48, 50/1, 50/2, 50/3, 51/1, 51/2,51/3, 54/1, 54/2, 55/1, 55/2 · Marco Cantonati 31/1, 31/2, 32/1, 32/2, 32/3, 34/1, 34/2, 35/1, 35/2, 39 ·Massimo Capula 134 · Ulderica Da Pozzo 9, 10, 27, 28, 46, 58, 110, 139, 148, 151, 153 ·Adalberto D’Andrea 6, 64, 132 · Massimo Domenichini 141 · Maria Manuela Giovannelli 60/2 ·Luca Lapini 90, 92, 98, 99 · Valeria Lencioni 20, 100 · Bruno Maiolini 56, 60/1, 65/2, 68, 71, 74/1, 74/2,79/1, 112, 145 · Mauro Marchetti 124 · Michele Mendi 95 · Andrea Mocchiutti 23 ·Giuseppe Muscio 26, 42, 52, 119, 120, 130, 135, 136 · Karin Ortler 40, 45, 49, 53 ·Sergio Paradisi 85, 87 · Natural Park of Foreste Casentinesi (Nevio Agostini) 7, 18, 29, 80, 122, 129, 147 ·Roberto Parodi 96, 97 · Ivo Pecile 13, 66 · Margherita Solari 47/2, 59, 116, 150 Fabio Stoch 62, 102, 103/1, 103/2, 114, 115, 138 · Roberto Zucchini 65/1, 67, 70, 79/2, 91, 93, 127

©2003 Museo Friulano di Storia Naturale · Udine

All rights reserved.No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form orby any means, without the prior permission in writing of the publishers.

ISBN 88 88192 10 7

Cover photo: springs of Arzino in Carnia (Friuli, photo by Ulderica Da Pozzo)

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Sergio Paradisi

Hydrogeology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Mauro Marchetti · Mario Panizza

Flora and vegetation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Marco Cantonati · Karin Ortler

Invertebrate fauna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Bruno Maiolini · Valeria Lencioni

Vertebrate fauna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

Sergio Paradisi

Ecology of mountain streams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

Fabio Stoch

Conservation and management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121

Mauro Marchetti · Mario Panizza · Sergio Paradisi · Fabio Stoch

Suggestions for teaching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

Margherita Solari

Select bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156

List of species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157

ContentsItalian habitats

1Caves andkarsticphenomena

2Springs andspringwatercourses

3Woodlandsof the PoPlain

4Sand dunesand beaches

5Mountainstreams

6TheMediterraneanmaquis

7Sea cliffs androckycoastlines

8Brackishcoastal lakes

9Mountainpeat-bogs

10Realms ofsnow and ice

11Pools,ponds andmarshland

12Aridmeadows

13Rocky slopesand screes

14High-altitudelakes

15Beechforests of theAppennines

Mountains undoubtedly take on fasci-nating aspects when the sight ofsnowclad peaks rising into the sky,high meadows carpeted with beautifulspring flowers, and mysterious, awe-inspiring forests are accompanied bywater as an additional feature in agrandiose landscape.Man has always been attracted to run-ning water, whether as a turbulent rushof power gushing from the tongues ofglaciers, as myriads of silvery streamsspreading down hilly slopes, as thepleasure experienced upon seeing aclear stream flowing across a meadow,or as the deafening roar of waterfalls.In the past, man exploited mountainsfor some of his activities; nowadays heviews them as “picture postcard” landscapes, sufficiently far from large townsto be considered uncontaminated and rustically serene.In fact, this oleographic picture is far removed from reality. Steep slopes andthe resulting high speed of water flow, the low or very low temperatures, andreduced trophism all mean that mountain streams are rigorous and selectiveenvironments.Their animal and plant communities are poorer than those found in lowlandrivers, and are made up of specialized components. However, as specializa-tion also implies vulnerability, high-altitude streams are essentially vulnerableenvironments, by their very nature. Here, meteoric events produce an almostcontinual renewal in the landscape, preventing animal and plant populationsfrom reaching a settled maturation stage: as if the stream biocoenoses wereperpetual pioneers. In such a context, any unwise human intervention, albeiton a small scale, may upset the delicately contrived balance which makes

7IntroductionSERGIO PARADISI

Mountain streams have always attracted man

The Acquacheta in the northern Appennines

9forms of life possible. The traditional activities of mountain people (livestockrearing, forestry) had generally limited consequences on the stream ecosystem,as at high altitudes there are few polluting sources and villages or towns aresmall. In recent years, the well-known phenomenon of abandonment ofmountain areas (particularly high mountain ones) has greatly reduced humanactivities. At the same time, and as a consequence of this demographictrend, various kinds of interventions were needed. They were neither smallnor uninfluential, and often deprived the stream and its landscape of theheavenly aura we have attributed to them so far.Dams, canalizations, various kinds of hydraulic arrangements, deviations andembankments all have a strong environmental impact aimed at controllingwater flow, to be balanced against their value for the safety of human settle-ments and hydraulic requirements. Streams are often viewed - paradoxically,since they are commonly perceived as absolutely natural - as nothing morethan sterile conveyors, preferential ways in which melted ice from glaciers orrainwater choose to reach the valley.The animal and plant communities which populate streams are not consideredwhen hydraulic operations are executed, and these often deeply modify andsometimes jeopardize those communities forever. The present volume deals with this issue, and also examines the geological,botanical and faunal aspects of Italian high mountain streams. When speakingof streams, we do not refer to a single, homogeneous habitat, but a complexnetwork of environments which often reveal very different geological and bio-logical aspects.Watercourses in the Alps and Appennines are mountain streams, as are thoseflowing down the lava spurs of Mount Etna and the small, temporary rivers ofinland Sardinia, the geological history of which has created a completely dif-ferent biogeographical world from that of the Italian peninsula. The icy, fast-flowing watercourses which descend from Alpine glaciers are streams, likerivers which on hot summer days are reduced to gravel beds and look morelike deserts than watercourses. This is why this volume does not cover all theenvironmental themes that the “stream” ecosystem provides. The presentwork is devoted to mountain streams in the strict sense of the word, definingthe geographical area of the Alps and northern Appennines and, further south,the streams of the Abruzzi and Latium regions.The volume covers all naturalistic aspects of streams, but also analyses thedangers which threaten the survival of their frail populations. We hope that thespread of knowledge may make us more aware of what we are about to loseand stimulate our will to preserve it.

8

An Alpine stream in winter

Waters flowing on the Earth’s surface make up the so-called superficialflow, a subject studied by branches of Earth Sciences such as hydrology,hydraulics, and geomorphology. Parameters relating to fluid physics (thefield of hydraulics), river geometry and the development of the hydrographicnetwork (hydrology), the structural factors of the catchment basin (lithology,degree of fracturing, etc.) and climatic conditions, which influence rivermodelling processes (geomorphology) are all necessary to understand thecharacteristics and evolution of watercourses.Rivers in the Italian Alps and Appennines differ greatly from one another, asthey are considerably influenced by the very varying rocks which outcrop intheir respective basins, and by very different relief energy, generally higher inAlpine basins. The Alps and Appennines also have different climates, as theformer are often located at higher altitudes, where the periglacial environmentdominates.

■ Geological setting

Italy is particularly rich in mountains and hills, which respectively represent35.2% and 41.7% of the entire surface area of the country. As is well-known,the mountains of the Alpine and Appennine chains belong to a very longmountain system stretching from the Straits of Gibraltar to Indonesia.The evolution of this mountain system is extremely complex: as regards thecircum-Mediterranean area, the various portions of the chain are a series oftectonically deformed stretches, in which the processes of shortening andoverthrusting of the continental crust did not take place in a homogeneousway. These phenomena date back to the Jurassic-Cretaceous boundary(about 150 million years ago).Subduction of the ocean floor ceased in the Cretaceous and the two edges ofthe Eurasian and African continents collided. Overthrusting began to involveincreasingly longer parts of the continental crust. The most active phase inthe Alps occurred during the Upper Eocene-Oligocene (40-20 million yearsago). The orogenetic phase continued into the Neogene and was particularly

11HydrogeologyMAURO MARCHETTI · MARIO PANIZZA

Ravines are typically created by streams flowing across hard rocks

13intense during the Miocene in the Tuscan Appennines, and in the Plio-Pleis-tocene in the external Appennines.Mountain chains in southern Europe are formed of overturned north-runningfaults: their structure is highly asymmetric, as they are composed of overlap-ping faults translated sometimes hundreds of kilometres. The Appenninechain overthrusts towards the Adriatic. The Alps are a well-defined geographical unit, about 1000 km long and 150-200 km wide, characterized by numerous peaks exceeding elevations of 3500m. The intense tectonic event in the Oligo-Miocene, which formed the Alps,was followed by an erosive phase which reduced the chain to a series of lowreliefs in the late Upper Miocene. The present conformation is due to later up-lift in the Plio-Pleistocene.The Appennine chain is about 1000 km long and only a few of its peaks ex-ceed 2000 m: the highest ones lie between the Abruzzi and Latium regions(e.g., Gran Sasso, 2912 m). Mount Etna is the highest (3223 m).The greatest differences between the Alps and the Appennines lie in the ex-tent of their tectonization, i.e., their degree of uplift and the ductile or fragilebehaviour of their rock formations. These factors directly or indirectly inter-act with others, such as the erodibility of rocks and climatic conditions, de-termining an erosion rate which varies significantly according to area. Themost significant difference in the evolution of mountain streams is certainlythe different lithogical composition of the outcropping soils in the Alps andAppennines.Despite their complexity, hard, erosion-resistant rocks outcrop throughout theAlps: intrusive and metamorphic ones in the west, calcareous in the centre

12

HELVETIC PREALPS M. ROSA SESIACERVINO

EXTERNAL DOMAIN SIMPLO - TICINES NAPPES

Geological sketch of a section of the WesternAlps, showing overlapping nappes in themountain chain.The Alps rest on a pre-Triassic basementcomposed of granite or metamorphic rocks whichare harder than the sedimentary cover. This hardbasement outcrops in the Western Alps.The Southern Alps, which comprise almost all thecentral and southern Alps, are calcareous, andrest on a paleo-African basement overlaid by

layers of sediments (and rare vulcanites) over 10km thick.Compression during the formation of the Alpsand the development of a series of sliding planes(faults) in the north gave rise to the subsequentthrusting, folding and shrinking southwards ofthese layers.Yellow: Helvetic domain; green: Penninic domain(light blue: Piedmont area); orange: Austro-Alpinedomain. A stream carving its way through mountains in the Aurina Valley (province of Trento)

covers, sandstone in the Tuscan-Emilian and Romagna ridge, limestone inthe Umbrian-Marches sequence, the crystalline and metamorphic rocks ofthe Apuan Alps, and the remains of the metamorphic basement with granitoidintrusions (which formed during the Hercynian orogenesis, dating back to theend of the Carboniferous, about 300 million years ago) of the Calabrian-Peloritan arc.This variety of rocks implies varying resistance to external agents and sur-face water flow, and thus also influences solid transport by watercourses.The total solid transport of the Appennine rivers has a higher percentage ofsuspended components than bottom sediments, in comparison with Alpineones.Another difference lies in the general distribution of relief energy, also de-fined as relative altitude. The mean altitudes of the various catchment basinsare greater in the Alps, as shown by the highest peaks of the two chains.High altitudes influence the microclimate of catchment basins and thereforethe type of water supply: the highest ones have nivo-glacial situations. Iceand snow also imply considerable physical disintegration (cryoclastism), ca-pable of forming great quantities of debris. This is carried to rivers by surfacewater flow, the force of gravity and avalanches.Alpine catchment basins are also usually larger than Appennine ones, andthis generally influences the supply, flow and length of watercourses.The two mountain chains also underwent different glacier modelling process-es. During the last glacial maximum, which ended about 15,000 years ago,the Alps were buried under a single ice cap, from which only the highest andsharpest peaks emerged, whereas the Appennines had small glaciers whichoriginated near the highest north-facing ridges. Glaciers have not only mod-elled the main valleys, but have also produced huge amounts of sediments,most of which are still stored in catchment basins. This debris is easily carriedby streams in far larger quantities than those deriving from physical disinte-gration in present-day morpho-climatic conditions.

■ Hydrography

Catchment basins. Water flowing on relief surfaces is organized in hydro-graphic networks, and all watercourses, including occasional ones, drain acertain catchment basin. This basin is the area in which - assuming nil infil-tration and evapotranspiration, that is, imagining surface impermeable anddevoid of vegetal cover - any liquid or solid precipitation (rain, snow, hail, etc.)is conveyed to the main channel subtending water flow in the whole area.

1514

LIGURIAN

BASINOPENING UP. OLIG. / MID. MIOC. TYRRHENIAN OPENING UP. MIOC. / PLIO.-P

LEIST.

ALPINE/SOUTH ALPINE LIMIT

PO PLAIN

GELA - CATANIA FOREDEEP

ADRIATIC FOREDEEP

BRADANIC FOREDEEP

IBLEI FORELAND

GARGANO FORELAND

SALENTOFORELAND

A

LP I

APPENNINE EXTERNAL FRONT

FOREDEEPS

FORELANDS

and east, and volcanic or dolomitic in the Veneto-Trentino (province of Trento)area. In the Appennines, lithologies are less coherent, being composed ofclay, marl and sandstone, with few crystalline or metamorphic rocks. Insome areas, volcanic rocks occur, in places made up of tuff and ash with lowresistance to erosion.However, less erodible lithologies stand out in the Appennines where thelandscape generally has gentle slopes: among these are the Latium volcanic

The Appennines, at the edge of the westernAfrican promontory (Adria microplate) featureforedeeps (Po Plain, Adriatic, Bradanic, Gela-Catania), later filled with sediments, on theedges of which are marginal continentalareas (forelands: Gargano, Salento and Iblei).The Appennines are composed of faultswhich originated in the Cretaceous, when theocean closed up, continental plates collided,and the Liguria-Provence and Tyrrhenianbasins were formed.

Compression caused tectonic plates to form,which became detached from the crustbeneath and overlapped. Orogenesis in theAppennines gave rise to anti-clockwiserotation of the Appennines and the Sardinian-Corsican unit, which caused the Liguria unitto slide over the Tuscan one during theOligocene. The southern Alpine and northernAppennine margins warped downwards andcame into contact under the Plio-Quaternarymarine and fluvial deposits of the Po Plain.

sum) were deposited in some areas. At the same time, in land emergingabove sea level, hydrographic networks receded, due to regressive erosionstarting from the lowest sea level. The extent of this deepening of the hydro-graphic network may be fully understood if we consider that the depressionbase of the main pre-Alpine lakes (Garda, Maggiore, Como, Iseo) is more than500 m below the present-day sea level. Even though these lake depressionshave been filled in by sediments over the last 5 million years, their bottomsare still below sea level.Other critical periods for the Alpine and Appenine hydrographic networkswere the great Pleistocene glaciations (1,800,000-10,000 years ago). In theAlps, glacial deposits identify at least five peaks which correspond to thegreat glaciations, called Donau, Günz, Mindel, Riss and Würm.During cold phases, catchment basins underwent complex, non-homoge-neous situations all along the Italian peninsula. The Alps, for example, werecovered by a single great ice cap extending to the Po Plain, from which onlythe highest reliefs emerged. Precipitation was less abundant than now, due tothe establishment of anticyclonic conditions over the glacial mass.The surrounding plains were steppe-like (dry and cold), and reliefs were cha-racterized by intense glacial processes which contributed both to remodelling

17

One catchment basin borders on others and is separated from them by aboundary called a watershed. Surface and subterranean watersheds do notalways coincide, as infiltration may produce subterranean flows towards otherbasins (loss) or from them (gain). The pattern of the hydrographic network of a basin, composed of the mainwatercourse and its tributaries, is called drainage pattern. It may take onmany different forms, mainly according to geological structure.

Evolution of a hydrographic network. The development of the hydrographicnetwork of the entire circum-Mediterranean area, including the Italian reliefs,was greatly influenced by an important event which occurred during theMessinian (Upper Miocene, 4-5 million years ago), when the Mediterraneanwas isolated from the Atlantic Ocean. Until then, the two had communicatedwith each other through two passages, one north of the Betic chain, in pre-sent-day southern Spain, and another south of the Rif chain, in present-dayMorocco. The approach of Africa to Europe closed both passages (first north,then south) in a few tens of thousands of years.The result of this closure was the almost total evaporation of the Mediter-ranean during a hot period, to such an extent that evaporites (especially gyp-

16

a b

d

c

e f

Dendritic drainage patterns (a) are typical of soilscontaining homogeneous clay, such as the hills ofthe northern Appennines.Parallel networks (b) are influenced by high-gradient slopes, like those of Alpine valleys.Rectangular networks (c) are associated withfaults and fractures and are typically found

in the Trentino Prealps.Radial networks characterize isolated reliefs, e.g.,the Euganean Hills (centrifugal, d), or depressionssuch as the volcanic lakes of Latium (centripetal, e).Deranged networks are found in geologicallyyoung or particularly eroded areas, such as theCarso (f).

Catchment basins and hydrographical networksmay be analysed from the morphometric point ofview by dividing them into hierarchicallyorganized streams.First-order streams are fed by springs orstreams; two first-order streams unite to form asecond-order stream; two second-order streams

unite to form a third-order stream, and so on.Second-order streams subtend basins of thesame order. These basins constitute sub-basinsof higher order basins, e.g., the catchment basinof the stream Isorno, between Piedmont and theCanton of Ticino (Switzerland) and its catchmentbasin.

2

2

22

2

2

2

2

3

3

2

2

3

42

2

22 2

4

5

2

2

2

2

3

2

2

3

3

2

23

2

0 2 4 km

5

1st ORDER

2nd ORDER

3rd ORDER

4th ORDER

5th ORDER

BASIN LIMIT

3rd ORDER BASIN5th ORDER BASIN LIMIT

2nd ORDER BASIN

1st ORDER BASIN

4th ORDER BASIN

during the last glacial maximum, gravel forming alluvial fans was deposited,and now makes up the feed area for the Emilian plain.After the last glaciation (Holocene), changes in the network were minimal andinfluenced the type of vegetal cover, and particularly its density. This waspartly conditioned by the climate, with slight variations in temperature and hu-midity during the Holocene, but mostly by the rise in human populations andtheir relative activities, starting from the Neolithic and even more in Romantimes. Several periods may be identified: severe network erosion followingdeforestation (especially in the Neolithic, in Roman times and the modernage), and minor erosion, in the event of stability, following mountain aban-donment and deforestation, as in the early Middle Ages or the second half ofthe 20th century. The latter period is one of the most difficult to interpret, asabandonment of mountain areas, which causes reafforestation, accompaniedother human actions, with contrasting effects.Abandonment itself, for instance, produces increased soil erosion in the shortterm, as woodland and slope maintenance are not carried out; lack of controland economic interests may give rise to the practice of deliberately settingfire to vegetation, resulting in large-scale erosion in the rainy season. Artificialoperations (works to regulate water flow, artificial reafforestation, etc.) havethe opposite effect, i.e., they thwart erosive processes.

Watercourse supply. Supply to watercourses is one of the most importantparameters which determine the quantity and quality of available waters instreams, as well as their regimen, or seasonal flow capacity. Watercourseswhich drain small basins with homogeneous lithologies are characterized bysimple supply due to precipitation, melting of ice or snow, or the emergenceof aquifers. In larger basins, water supply is complex, and is influenced by thevarious types of flow supplied by tributaries.There may be pluvial supply when the water flowing in rivers comes from rain-fall. Rivers with this kind of supply have regimes characterized by high or lowwaters, according to periods of maximum rainfall or dry seasons respectively.This seasonal trend is therefore influenced by the general climatic conditionstypical of the catchment basin.In the northern Appennines, where feed is typically pluvial, high waters aremore common in autumn than in spring. Low waters are typical of winter andespecially summer, as a consequence of both high evapotranspiration andreduced supply. In areas with particular climatic conditions, like Liguria orsouthern Piedmont, the proximity of the Alpine and Appennine chains to thecoast interferes with air masses coming in from the Atlantic, which may cause

19

of the main Alpine valleys and to overall deepening of the network. In theseperiods, many base levels were reshaped; glacial excavation of the main valleysand the settling in them of very thick layers of ice supported higher base levelsfor side tributaries, producing what today are suspended valleys, where thetributaries flow into the main valley over a “throw”, giving rise to sometimesspectacular waterfalls.During the glacial epochs, debris was produced in great quantities and thenetwork deepened; huge deposits of sediments, for instance, accumulated inthe valleys at outlets to the plain, as far as the Po itself. The sea, the level ofwhich was about 110 m lower than it is today, did not influence the mountainportion of the network to any significant extent.During the glacial phases in the Appennines, there were no large glaciers, andnot even tongues of ice reached the surrounding plains. The landscape wasdominated by periglacial (cryonival) conditions; only in the innermost areas ofthe northern Appennines (Tuscan-Emilian ridge) and on the Abruzzi reliefs didsmall or medium-sized glaciers appear.Periglacial conditions implied intense physical disintegration, which was notfollowed by corresponding deepening of the hydrographic network. The lattercould not remove all the sediments produced on its flanks and conveyed toits watercourses. “Grèzes litées” are the characteristic deposits still foundon the flanks of the Umbrian-Marches regions. In the Po Plain, for instance,

18

An Appennine stream (Ponte della Brusia, Bocconi, Forlì)

Emergence springs ( a ) have variouslocations and may temporarilydisappear as the flow of the aquifervaries during the year. If they emergein a valley, they appear at loweraltitudes as the watertable sinks, andreach high altitudes during maximumlevel phases. If they are in a cavity,they may disappear during lowwatertable levels. Overflowing springs ( b ) originatewhere waters in subterraneanchambers touch an overflow thresholdor reach the surface.Contact springs ( c ) are very commonand flow out when the aquifer flows inpermeable soil after touching animpermeable formation. This contactmay be stratigraphic (transgressions,etc.) or tectonic in origin (overthrusts,faults, etc.), or due to recent formsand deposits (landslides, moraines,

floods, etc. on less permeablelithotypes underneath). These springs have fixed locationswhich cannot be altered by changesin watertable level. When the latterchanges, they may vary in flow, orgush out only when the watertablelevel is high.Karstic springs ( d ) in carbonaticmassifs are a typical example: here,permeability is principally due to flowin cracks and fractures rather than tothe permeability of the rock itself.Barrage springs ( e ) result fromsubterranean water that emergeswhen impermeable obstacles hinderits flow.Fissure springs are caused by thepresence of faults, fractures and anyother type of preferential course, e.g.,karstic conduits, which allow water toflow out at a precise spot.

Types of springs Mauro Marchetti · Mario Panizza

a b

d

e

c

21intense, late summer storms which areresponsible for catastrophic floods.Similar situations are typical of theCalabrian region and to a certain ex-tent the whole western Appenninechain. Another peculiar situation maybe found in the Friuli and Veneto Pre-alps, where cold air masses wedge infrom central Europe and sometimesSiberia. These cause fronts to settle inthe area for long periods, especially inautumn, when they give rise to abun-dant rainfall.Glacial supply occurs when water-courses derive from the melting of ice.In this case, high waters are recordedin periods when melting is intense,i.e., in summer, whereas low watersare typical of winter.

When water supply does not depend on the melting of ice but of snow, highwaters are anticipated to spring and decrease in warmer periods, when thesnow cover is reduced. Snow supply prevails in the high-altitude basins ofthe Italian mountain regions; high waters peak in May-June and then de-crease until the following spring.Watercourses with snow supply may be found at high altitudes in the WesternAlps, and the water consists of melted ice and snow. Many tributaries of theDora Baltea, Dora Riparia, Sesia and Ticino are supplied in this way, as wellas some tributaries of the Adige along the Eastern Alps.

Springs. In mountain streams, springs may determine the regime of water-courses. When the quantity of water only amounts to a trickle, the result is asmall pool; when the flow may be gauged, it is called a “true spring”. Manynames are given to water originating from springs: true springs, “fountain-heads”, “veins”, and in the case of anthropic intervention, “fountains”. Streams carry water emerging from aquifers. In the case of permeable rocks,aquifers originate in sediments in which the speed of water flow depends onthe slope and permeability of the terrains crossed. Springs originate when theroof of the aquifer meets the topographic surface. A spring is thus an area,small or large, where the subterranean aquifer meets the surface of the

20

Meltwater is a form of supply for mountainstreams

2322 ground and emerges. Water may leave the aquifer because it filters throughsediments, porous rocks, or preferential conduits, generally discontinuoussurfaces (stratified surfaces, formations with different degrees of permeability,cracks, faults, etc.). There are many kinds of mountain springs, among which are emergence,overflowing, contact, barrage, and fissure springs.Springs may be isolated, grouped in restricted areas, or aligned along parti-cular geological structures (for instance, between permeable and imper-meable formations). These alignments may be particularly frequent, as flyschin the Appennines or sandstone overlying the fine, impermeable rocks of thehigh Emilian Appennines (e.g., at the foot of the “Pietra di Bismantova”).

Chemico-physical characteristics of water. Mountain stream waters arecharacterized by a thermal regime which depends on their supply, and bychemical composition which depends on the surface terrains they cross -and, particularly for spring waters, on the composition of the rocks crossedbefore reaching the surface. Water chemistry is determined by dissolvedions. Their transport in solution does not depend on watercourse energy, i.e.,water flow and speed, but rather on the composition of the rocks crossed andtheir aggressivity (pH). The most common dissolved ions are carbonate (CO3

=), chlorine (Cl-) and sul-phate (SO4

=) ions, as well as sodium (Na+), potassium (K+), calcium (Ca++) andmagnesium (Mg++) cations, and dissolved silica (SiO2).The predominance of some ions over others depends on the terrains crossed,for example, waters flowing inside carbonatic massifs have basic pH and arerich in calcium ions and carbonates in general. Waters that cross crystallinemassifs where quartz and feldspars abound (e.g., granite, gneiss and schist),have acid pH and are rich in silica, like those of the innermost part of theAlpine chain. Waters crossing a particular terrain, like Triassic gypsum in theUmbrian-Marches chain, are rich in calcium and sulphates.Sodium and chlorine waters are found in salty soil recently abandoned by thesea (generally in coastal plains) or areas with mineral springs. Higher concen-trations of magnesium ions are recorded in areas rich in this element, as inthe Dolomites. Transport in solution is gauged through laboratory tests which determine thecontents of dissolved ions; this datum is expressed in different units of mea-surement. One of the most common is hardness, i.e., the content of calciumand magnesium in water (total hardness).Hardness is measured in hydrotimetric degrees, the most common of which

are French degrees (1°F corresponds to 10 mg/l of Ca++ ion). According to thisunit of measurement, waters are classified as: very soft (0-7), soft (7-14),moderately hard (14-22), quite hard (22-32), hard (32-54) and very hard (>54).Total solid residues at 180°C are easy to find: a litre of water evaporates at180°C. Waters derived from the melting of snow are particularly acid, due tofew dissolved cations and abundant carbonic acid.In some areas of the Italian reliefs water chemistry may be modified byanthropic causes, mainly related to the intense exploitation of Alpine areasby tourists. The consequences of this great demographic pressure has led tosometimes significant increases in pollutants: coliform organisms, heavymetals, nitrates and phosphates.Abnormal increases in hydrocarbon and chloride are recorded near mainroads, due to the scattering of chlorinated salts for de-icing. Livestock farm-ing areas (cattle-breeding in the Alps and sheep-breeding in the Appennines)lead to high values of dissolved nitrates and nitrites.

Hydraulic systems. Watercourses may be divided into two groups: riversand streams. The two groups partially overlap over a wide transition area.A river is a perennial watercourse with low speed and slope (less than 0.5%gradient). Streams or seasonal torrents are characterized by higher speeds andgradients; the term torrent, in Latin torrens, derives from “torreo”, or bubbling.

High-altitude karstic area (Julian Alps) without surface drainage network

Velocity

Water velocity is the best indicatorof stream energy. The faster watersflow, the more intensely stream bedsare eroded; slow-moving waters giverise to sedimentation processes.Velocity is not constant or regularalong streams; in rectilinearstretches, fast waters usuallyconcentrate in the middle of thechannel, just under the free surface;in curved ones, they concentratenear the concave bank.

In the early 20th century, it wasalready clear that erosion, transportand sedimentation all depend onwater velocity, as shown inHjulström’s diagram of 1935.This demonstrates that the finestparticles (diameter less than 0.05mm) are not sedimented, even if thewater is almost still, but float insuspension as far as the streamsreach the lakes or seas, whichrepresent base levels

Stream discharge

Stream discharge (Q) is the volume ofwater flowing in a stream in a specifiedunit of time, and is expressed by theformula:Q=Avin which A is cross-section area and vis average stream velocity. Streamdischarge is measured in m3/sec orsometimes in l/sec, by calculating thehydrometric level of water.Their trends in time are analysed withdiagrams called hydrograms.

In Italy, the National HydrographicalService provides many measuringstations, and the data collected arepublished.Past floods recorded over longperiods and then statisticallyprocessed, can predict peakstream discharges in 100, 200 oreven 1000 years. Those withparticular return periods are used todesign special works alongwatercourses.

Velocity and stream discharge Mauro Marchetti · Mario Panizza 2524 This term is often also used in a figurative way to describe the intensity offlow in particular circumstances, like “a torrent of words”.The speeds of mountain streams vary and are affected by water flow andtype of supply. Low waters may be perfectly calm and their speed very low,about 0.1 m/s, whereas high-altitude waters have a high speed, over 10 m/s.Therefore, even if streams have minor total flows, they have a far greatercompetence.Watercourse competence is determined by the maximum size of the singleclastic rocks carried. This size is strictly controlled by the stream speed and itsdepth. Instead, total solid transport is proportional to the water flow. Increasedvolume of transported material (solid load) and corresponding decrease inthe particle size of transported material (competence) are observed assprings flow from the upper parts of their catchment basins to the rivermouth. The collection and sedimentation which occur along streams change theirlongitudinal profile. Erosion along a portion of the stream lowers the gradientof the watercourse downstream and raises it upstream, increasing the ero-sion rate upstream and lowering it downstream. Similarly, sedimentationalong a portion of the stream lowers its gradient upstream and raises it down-stream. When every part of the longitudinal profile maintains the same gradi-ent over a sufficiently long period (e.g., one year), the watercourse is said tohave reached balance.Streams reach their characteristic balanced profile through erosion and sedi-mentation processes. When this occurs, the whole volume of debris whichreaches the stream bed from nearby slopes and upstream, is carried awaydownstream. From the viewpoint of transported sediments, a balancedstream therefore has a nil balance. A diagram with the ordinates showing ele-vations above sea level and the abscissa the distance from springs, will showthat the longitudinal profile of a balanced watercourse is theoretically hyper-bolical, with gradients steadily falling from spring to river mouth.The river mouth is a fixed point of reference, called base level, below whichwatercourses cannot deepen their beds. The general base level is the sea,although there may be local base levels due to the confluence of streams inhierarchically more important watercourses, or their flow into natural or arti-ficial lakes.Huge clastic concentrations, larger than those of stream competence, arevisible along mountain streams. These large pebbles or boulders are notcarried by the stream water, but by gravity along its flanks or exhumation bywater of smaller clastic rocks, until the channel banks and bottom are almost

Hjulström’s diagram, showing that erosion,transport and sedimentation all depend onwater velocity.x: diameter of debris in mm;y: current velocity in cm/sec

+

+

0.001

1000

100

10

1

0.10.01 0.1 1 10 100mm

cm/s

ec

RECTILINEAR STRETCH

CURVED STRETCH

CONVEX BANK

CONCAVEB

AN

K

EROSION

TRANSPORT

SEDIMENTATION

Distribution of lines connecting points wherethe current has equal velocity in rectilinear (up)and curved stream beds (down).Fast currents are shown in red: in a curvedstrectch they are close to the concave bank

completely made up of immovablematerial. In such conditions, channelscannot be eroded further, as thecoarse clastic rocks protect underly-ing deposits with finer particle sizesfrom erosion.The arrangement of large rocks inmountain streams is very importantbecause it contributes to the forma-tion of clastic aggregates supportedby larger blocks. These determine thetypical terraced profile which Anglo-Saxons call “step and pool”. Thespacing and relief of this type of dis-continuity is important both to assessthe dispersion of energy in the stream,due to the roughness of the river bedand the hydraulic throws which areresponsible for downstream decelera-

tion at every step, and for the ecology of the stream itself, as shallow, faststretches alternate with calm, deep ones.Solid transport in mountain streams is deeply affected by the rocks of thecatchment basin, the stability of flanks near the stream, active processes pre-vailing in those reliefs, and the type of feed of the stream itself. Prevailingtypes of solid transport are thus impossible to define according to hydrauliccharacteristics (e.g., flows and speeds). Streams crossing easily erodible finerocks, like those of the Emilian Appennines, have higher suspended transportthan their bottom sediments. In such areas, mainly during intense autumnrains, the waters become cloudy following surface leaching of rocks in thesupply basin and slow gravitational processes along flanks.In streams supplied by ice meltwater, suspended transport makes watersmilky-blue in colour. Streams which cross areas with outcropping competentrocks - calcareous, dolomitic or crystalline - have more bottom sedimentsthan suspended components, especially if the material reaching the river bedderives from cryoclastism and if transport down slopes is due mainly to col-lapse rather than to surface leaching. Generally, there is a clear difference intypes of transport during high and low water phases. Low waters are charac-terized by little bottom transport, whereas suspended transport continues,particularly if clay or fine sediments are occur along the river bed.

2726

Large amounts of solids make waters milky(Savio stream, northern Appennines)

Steps and pools

■ Algae and aquatic lichens

In normal conditions, i.e., when disas-trous events like sudden, great floodsor chemical pollution have not oc-curred, the bed of a stream sparkleswith shades of colour ranging fromdark brown or black, to reddish, to allnuances of green and blue-green.Streams owe their bright colours to al-gae, aquatic lichens and mosses(whereby German scholars use theterm Vegetationsfärbungen = coloursdue to aquatic vegetation). The banks,unless artificially straightened or reinforced with concrete, are never bare, butrichly covered with aquatic plants, bushes and trees which need increasinglyless water and become more and more intolerant of submersion with distancefrom the stream. While aquatic and hygrophilous mosses are frequent inspring areas, and higher aquatic plants prefer slow-moving waters with sandyor muddy bottoms typical of large plain rivers, mountain streams with fast-moving waters are characterized by algae. These organisms are generally as-sociated with beaches, or sometimes lakes, not with mountain streams. How-ever, even if often overlooked, they are quick at colonizing any watercourse,whether small or impetuous, in plains as in mountains.The term “algae” is commonly used, but it often inappropriately identifies truehigher plants which have adapted to life in an aquatic environment, such asthe water buttercup. The term is inaccurate also from a strictly systematicpoint of view, and is nowadays mostly used informally to indicate a highly var-ied group of organisms. “Algae” better defines aquatic plants of various sizesand with heterogeneous organization, without specialized vascular tissues,and not separated into the usual roots, stem and leaves (i.e., they are thallo-phytes, not higher plants).

29Flora and vegetationMARCO CANTONATI · KARIN ORTLER

Springs of Arzino in Carnia (Friuli): algae and lichens cover most of the emerging rocks

Vegetation along the banks of a stream

Cyanobacteria. Cyanobacteria oftencolonize the most inhospitable areas ofstreams, where environmental conditionsare the most severe, e.g., areas wherewater may flow suddenly, change andperiodically cease entirely, or rocks alongthe banks that are only occasionallysplashed or sprayed by turbulent waters.Cyanobacteria are also calledcyanoprokaryotes, as they do not have aneukaryotic structure like algae, but areprokaryotic, like bacteria. Unlikephotosynthetic bacteria which containbacteriochlorophyll, they containchlorophyll a, and their photosynthesis isoxygenic like that of algae, mosses andhigher plants. Many of them have asufficiently high number of characteristicsto be taxonomically analysed withmethods traditionally applied to algae,i.e., morphological observations byoptical, Scanning or TransmissionElectron Microscopyes.So far, cyanobacteria have therefore beenstudied by phycologists as “blue-greenalgae” or “cyanophytes”.

However, “los bacteriólogoschauvinistas”, as the well-known Spanishecologist and phycologist RamónMargalef defined them, claim thatcyanobacteria should only be studiedusing methods applied to bacteria.This controversy is based on thestructural (prokaryotic) simplicity of theseorganisms, which resembles that ofbacteria and enables them to colonizeinhospitable environments like the Arctictundra, rocky mountain slopes and high-temperature waters (for this very reason,bacteria were among the first organismsto appear on the Earth billions of yearsago). In these environments,cyanobacteria are subject to intense solarradiation, particularly by ultraviolet light,which can seriously damage their DNA.They react with a whole series ofadaptations, like actively moving awayfrom excessive light, generating efficientmechanisms to repair molecular damage,and producing photoprotectivesubstances. Nowadays, concern for thereduced ozone in the upper atmosphere

31Algae range in size from few thousandths of a millimetre in the case ofcyanobacteria (blue-green algae) to tens of metres in giant brown algae(Macrocystis), which grow on ocean shores. The cells of these plants presentthe two main structural patterns of the animated world: prokaryotic, havingcells without a differentiated nucleus, typical of bacteria and cyanobacteria,and eukaryotic, with a nucleus clearly distinguished from the cytoplasm andenveloped in membranes, typical of all other organisms. The feature these al-gal types have in common is the way in which they procure energy for life,through oxygenic photosynthesis, by means of a green photosynthetic pig-ment called “chlorophyll a”, typical of both cyanobacteria and plants. How-ever, individual algal groups differ enormously for the other pigments theycontain (accessory and photoprotective), as well as for their ultrastructural,physiological and biochemical characteristics and reproductive system, inthe same way as man is different from a sea-urchin or an insect.

■ Seasonal variations of algae in streams

In temperate climates, seasonal trends affect the presence and development ofmany species of algae in streams. The cyanoprokaryote Phormidium autum-nale, as its name suggests, is usually found in autumn; the chrysophyte Hydru-rus foetidus prefers the cold months of autumn and winter; the rhodophyteBangia atropurpurea develops in early spring. The variations in the abundancesof these macroalgae are macroscopically visible and can be quantified by mea-suring cover and thickness on the spot. As regards diatoms, this is only pos-sible for exceptional blooms of some species occurring in specific seasons(e.g., Diatoma spp., Gomphonema olivaceum var. calcareum, Melosira varians).Many works devoted to streams indicate that variations of the most abundantspecies in diatom associations, in percentual terms, are not very great.

30

MARCH APRIL MAY - JUNE

1 m

m

CYANOBACTERIA

DIATOMS

GREEN ALGAE

Seasonal variations in algal populations (sizes of the individual algae are indicative and colours are onlyevocative) on stream rocks and pebbles (microscopic aspect)

Algal groups in mountain streams Marco Cantonati

Dark brown spots are colonies of Chamaesiphon geitleri, a cyanobacterium typically found in mountainstreams with carbonate substrates and clean, gushing waters. Right: cells of the cyanobacteriumenveloped by an irregular sheath, as seen under the microscope (1000 X)

are “typical” glacial streams,characterized by high discharge(especially in the hottest hours of the dayin spring and in summer), and rich insuspended sediments (glacial flow).Otherwise, these algae are found inalmost any humid area, from cracks in thedesert floor to the oceans. They aremicroscopic (a few thousandths of amillimetre) unicellular organisms, but theymay aggregate in large groups which,when they bloom, form golden to darkbrown patinas, velvety covers, or thinfilaments. This is the case of speciesbelonging to the genus Diatoma, whosecells adhere to one another forming longbands and, in particular conditions,accumulating to cover the beds of slow-moving watercourses.Every diatom cell is contained in twovalves made of amorphous silica,structurally very similar to opal and glass.These valves fit together like the box andlid of a shoe box: bilateral and radialsymmetries are the most common typesamong diatoms. According to this simplecriterion, diatoms are subdivided into twolarge groups, Pennales and Centrales.This subdivision has deep ecological andmorphological significance, as it is basedon the two large habitats colonized bydiatoms: benthic, i.e., shores andwatercourse bottoms, and planktonic, i.e.,free waters typical of lakes and oceans.Diatoms are so small that they are littleknown to non-specialists, but they arevery important in aquatic environments.They frequently dominate oceanicplankton and constitute the basis of thefood chains on which large-scale sectorsof the fishing industry, and therefore thenourishment of entire human populations,depends. They make up about a quarter

of global primary production, exceedingrainforests and savannahs which are byfar the most productive terrestrial biomes.The elegant shapes of diatoms are still asource of inspiration for artistic works, inwhich valves are embedded in resin andjuxtaposed on slides. The valves owetheir beauty to the rich and complexseries of their morphological details(spots, lines, bands, etc.) which are thesignatures of the various species.Identification is carried out by arrangingthe valves on slides after cleaning themof organic substances and carbonates.Identification of diatom species istherefore based on the structural detailsof the silicic “box” which contains theircells. One of the most evident structuralcharacteristics of Pennales is the thin slit,called raphe, which runs along the valve.It has long been thought that thisstructure enables certain diatoms tomove, but the exact mechanism is verycomplex and is still being studied.The cell seems to emit “small molecularrods” from the raphe opening: these rodsadhere to the substratum at one end,and hook themselves to the cellmembrane on the other. The cell movesforward by contracting, the rods unhook,and then the process is repeated.The ability to move actively is particularlyimportant for species living on mud(epipelic habitat) or other soft substrates,as the micro-algae are enabled to moveto illuminated surfaces when they needto (species of the genera Navicula andNitzschia are typically mobile andepipelic).Other species (like those of the genusCocconeis) have a raphe only in one ofthe two valves, and anchor themselvesfirmly to hard substrates (e.g., stones

33requires deeper knowledge ofcontrivances adopted by organisms toprotect themselves from ultravioletradiation, and these physiological andbiochemical aspects are therefore studiedvery closely.The main accessory pigments ofcyanobacteria are blue phycocyanin andred phycoerythrin, which endowmountain stream beds with brightcolours: red or reddish in some areas oron rocks; small, dark brown or turquoisespots glowing under stones, and darkgreen spots on pebbles. Some speciesprotect themselves from dehydration withstrong sheaths enveloping their cells, likeChamaesiphon polonicus, which isgenerally found in areas of the streamcharacterized by occasional or seasonallow water or even none at all. Streamcyanobacteria prefer epilithic substrates,i.e., rocks and pebbles. They may alsogrow on other substrates, such as moss,

aquatic plants, or other cyanobacteria(like Chamaesiphon amethystinus, whichis found on the filaments of anothercyanoprokaryote, Tolypothrix distorta).Most taxa (= taxonomic groups, likegenera and species) are widespread.However, there are also very rare species,such as the above-mentionedChamaesiphon amethystinus. In 1999,Eugen Rott and co-workers identifiedalgae in Austrian waters (analysing 225watercourses from various aspects), andclassified almost half the cyanobacteriaas “very rare” on the basis of theirfrequency. Many taxa are good indicatorsof water quality.

Diatoms. Diatoms make up the largestgroup of algae as regards number ofspecies and individuals in a stream and,generally, in aquatic environments. Thereare few kinds of watercourses whichdiatoms do not colonize, among which

32

Banks of a mountain stream covered by the efflorescence of the microalga Diatoma. Bottom right:bands formed of algal cells (about 60 X); top right: the silicic frustules of these diatoms have arectangular section when seen from the side (400 X)

occurs and in summer with patches ofgreenish filaments or green crusty covers.Tufts of green filaments frequently growon aquatic moss. These algae belong tothe large group of green algae orchlorophytes, the only ones to contain thesame chlorophyllic pigments (chlorophylla and b) and the same reserve substance(starch) as mosses, ferns and higherplants. Areas of the stream subject toflow variations reveal unbranchedfilaments of green algae of the orderUlotrichales. Those belonging to the orderZygnemales are found in calm, cleanwater. Microscopic examination easilyidentifies the three most common generaof this group according to the shape oftheir chloroplasts: spiral in Spirogyra,band-like in Mougeotia and star-shapedin Zygnema. Representatives of theDesmidiales are rare in streams, althoughthey may be found in small side bayswhere sand and organic substances aredeposited. These are considered amongthe most beautiful of all algae. Desmidsare frequently found in environments likepeat-bogs, and are characterized by cellssymmetrically arranged on both sides of anarrow waist or isthmus, with a richlydecorated cellulose wall which makesthem look like tiny jewels. Springs and

streams on carbonatic rocks maysometimes reveal the presence ofOocardium stratum, a rare, clearlydeclining species. Its cells are insertedlike plugs in tubular calcareous deposits.Members of the Cladophorales arefrequently found at mid-low altitudes,particularly on limestone rocks or in waterrich in nutrients, where they coversurfaces with their dense, branchingfilaments. Their most common genus isCladophora, which is characterized byparticular branching and multinucleatecells, as microscopic examination reveals.Green algae, however, do not necessarilyturn streams green. In spring andsummer, the banks of at least seasonallyfast-flowing and turbulent mountainstreams are coloured orange and red. Thecolour is actually due to green algae ofthe order Trentepohliales, located on theevolutionary line which led to the higherterrestrial plants. Their cells are filled witha mixture called hematochrome,containing carotenoid pigments.

Charophytes. In the past, charophyteswere classified as green algae, as theyshare the same pigments (chlorophyll aand b) and reserve substances (starch).Today, charophytes or stoneworts are

35and rocks, epilithic habitat) by means ofmucilage produced by the raphe itself. Inyet other cases, they adhere with strongmucilaginous stalks which are secretedby pores at one or both ends of thevalve. The variety of movement andadherence mechanisms enables diatomsto colonize all areas of mountainstreams: central zones with fast-movingwater, or small side bays where organicmaterial collects easily.The many species and their differentecological needs allow the colonizationof various kinds of streams, from waterswith very little mineralization to those richin carbonates, from clean waters toothers organically polluted orcontaminated with heavy metals.

Chrysophytes. Chrysophytes, or golden-brown algae, are similar to diatoms asregards their accessory pigments andreserve substances, and includeplanktonic species with silicic scaleswhich form typical silicified cysts.However, only one species of this grouplives in mountain streams, Hydrurusfoetidus. Fringed filamentous structures,several tens of centimetres long, whichcharacterize these chrysophytes and turnthe beds of mountain streams almost

black, particularly on carbonatic rocks,are often seen in autumn or winter.Great quantities of these algae may evenbe smelled in areas with a moderateincrease in algal nutrients (e.g., near anAlpine cattle barn). This smell(unpleasant, recalling that of rotten fish)becomes pungent if one of thesefilamentous, mucilaginous structures issquashed - hence its name “foetidus”.Microscopic examination reveals that thecells of this alga, which are greenish andgolden-brown ovoid structures a fewthousandths of a millimetre in size, areactually immersed in a mucilaginousmatrix inside the filamentous structure,technically called coenobium. Thespecies is usually found in cold waters,from the mouths of glaciers to mediumaltitudes. Flow and light may play animportant role in the development of thisalga, since it tends to reduce its presencein summer even in mountain springswhere water temperature is almostconstant and low also during summer.

Chlorophytes. In mountain streams, thebrown shades of diatoms andchrysophytes alternate with the blue-green, turquoise or reddish cyanobacteriaand, in particular, when organic pollution

34

A fast-flowing mountain stream. The felty red covers on rocks are due to the green alga Trentepohlia sp.Right: enlarged photograph showing branched filaments, which owe their red colour to the presence ofcarotenoid pigments

The filamentous structures are cenobia of Hydrudus foetidus, typical of fast-flowing stream stretches,particularly in autumn and winter. Right: the cells of Hydrudus foetidus (green ovoid structures) underthe microscope; the elongated, arched shapes on the right are cells of the Diatoma Fragilaria arcus

■ Biogeography of algae in streams and endangered species

The importance of biogeography in explaining algal distribution is difficult tointerpret. The same species may be common to several mountain chains indifferent continents (e.g., the Alps and the Himalayas), whereas others seem tolive only in a single mountain massif. Some species of diatoms, for instance,although widely distributed, cannot be found in some areas: Fragilaria arcusvar. recta lives in Arctic and Antarctic areas and in eastern Asia, but not inthe Alps.Generally speaking, as most groups of algae develop resistance forms whichcan be efficiently carried by the wind, aquatic birds, etc., most species arecosmopolitan and widely distributed. As regards diatoms, this is particularlytrue of species living in polluted or moderately contaminated waters.Methods for evaluating the quality of waters based on diatoms are thereforeeasily applicable or adaptable to streams throughout the world. It is not sur-prising then, that there are no great differences between the algal flora ofAlpine and Appennine streams. In the Appennines, longitudinal distributionareas of algal species, detectable along watercourses, are compressed andlocated at lower altitudes with local variations.Natural causes and phenomena of organic pollution which generally increase

37generally considered an independentgroup, especially because of the peculiarstructure of their thallus and reproductivestructures. They generally live in stillwater, but may be found on the sides ofstreams, in secondary channels, or areaswhere the current is slow and finesediments deposit. They definitely preferclean waters and carbonatic substrates.Although non-specialists often confusethem with aquatic higher plants, they aremacroalgae. They look like, long, smallplants, extending for several tens ofcentimetres, with multi-cellular thallimade up of elongated internodal cellsand shorter nodal cells bearing whorls ofbranches, each of limited growth. Theplant is usually covered by carbonateprecipitates, which must be removed withdilute hydrochloric acid prior toexamination. Many species typically smellof garlic. The most common genera areChara and Nitella, which may formsubmerged meadows.

Xanthophytes. Green thalli of peculiarshape may be found in streams,sometimes so densely packed that theyresemble that kind of stiff synthetic spongeused by florists for flower compositions.They are not green algae, but a species ofthe genus Vaucheria, belonging to thexanthophytes or yellow algae. This groupdoes not contain chlorophyll b and itsreserve substance is not starch butchrysolaminarin. Xanthophytes may bedistinguished from green algae by usingreagents which colour starch, like iodine.Equally important and widespread, thegenus Tribonema has very differentmorphology. It includes several specieswhich form long, unbranched filaments inmountain streams.

Rhodophytes. Red algae or rhodophytesare very often found in seawater, and theirpresence in fresh water is relatively rareand limited to a few, albeit very interestingspecies.Hildenbrandia rivularis forms beautiful,bright red circular spots, especially inlow-altitude streams. Lemanea fluviatilishas thalli with nodose structuresseparated by internodes. It is arheophilous species (adapted to thecurrent) with a wide distribution instreams and which may even appear inglacial streams at high altitudes.The most peculiar species is Bangiaatropurpurea, a red filamentous alga,almost identical forms of which inhabitareas of varying altitudes, ocean, sea andlake shores, rocks and other hardsubstrates in various types of streams. Inthe last few decades, detailed studies onits morphology, reproductive cycle,ecophysiology (adaptation to differentdegrees of salinity in cultures in thelaboratory), karyology (analysis ofchromosome number, form and size) andlately, biochemistry and moleculargenetics, have aimed at determining ifthese sea and fresh water forms alikebelong to the same species, or if they areto be viewed as separate entities.Audouinella hermanni is frequently foundin mountain streams. It lives on rocks orother aquatic plants, where it formspurple-violet thalli a few millimetres long.

Phaeophytes. Very many species ofphaeophytes or brown algae live alongsea and ocean coastlines, including thelargest of all algae. Their presence infresh water is limited to a low number ofspecies (e.g., Heribaudiella fluviatilis),mainly found at low altitudes.

36

EPIPSAMMIC EPIPELIC

EPIPHYTIC

EN

DO

LIT

HIC

EPILITHIC

mudsand

The main habitats of microalgae in streams, showing algal populations typically associated withsubstrates, including those which may pierce through carbonatic rocks to reach the interior (endolithichabitat)

downstream, give rise to the typicallongitudinal distribution of algalspecies along watercourses. Highaltitudes are characterized by epili-thic species which live in clean, cold,fast-flowing waters (e.g., the cyano-bacterium Chamaesiphon polonicus,diatoms like Diatoma mesodon andFragilaria arcus, the chrysophyteHydrurus foetidus and the rhodophyteLemanea fluviatilis).Medium altitudes are marked byspecies which require some nutritivesalts and can withstand variations intemperature (e.g., diatoms like Cym-bella affinis and Cocconeis placen-tula, the chlorophyte Cladophora glo-merata and the xanthophyte Vaucheriageminata). Species which can toleratehigh quantities of nutritive salts andhigher temperatures (e.g., the cyano-

bacteria Oscillatoria spp., diatoms Navicula spp., Nitzschia palea and Surirellaovata, and desmids Closterium leibleinii and Staurastrum punctulatum) arefound at low altitudes.In view of the often wide distribution and intimate relationship between envi-ronmental conditions and algal species, attempts at drawing up “Red Lists”(i.e., of endangered species) for algae and particularly diatoms, have led tothe identification of some of the endangered aquatic environments in whichthese algae live. For diatoms, these are mainly nutrient-poor (oligotrophic)freshwaters.According to Horst Lange-Bertalot, who drew up the Red List of diatoms inGermany, protection of these environments is particularly difficult, as theyundergo not only direct impacts (e.g., organic pollution), but also receivesupplies of atmospheric pollutants (some of which may be nutrients) withprecipitation. As regards the distribution and rarity of algal species, muchstill remains to be done, especially in Italy, since the algal flora of large areashas not yet been explored or is still scarcely known.The presumed rarity and distribution of certain taxa may therefore be due tolack of available information.

■ Aquatic lichens

Not all the patinas and colourful crustsfound in mountain streams are due toalgae and cyanobacteria: many arecomposed of aquatic lichens.These organisms have not yet beenstudied thoroughly, and available in-formation is scarce. Aquatic lichens,like all lichens, derive from the associ-ation (symbiosis) of an alga (chloro-phyte or cyanophyte) with a fungus(ascomycete). The alga provides glu-cids (sugar) through photosynthesis,

and the fungus offers a protected environment and supplies sufficient waterand salts from outside. Covers with variously well-defined edges may oftenbe seen in streams.The colours of their thalli range from grey, black and dark brown to greenish,and they bear black ovoid structures. These are called perithecia and con-tain the spores of the fungus. The perithecia may be very obvious and looklike verrucas or warts - hence, the common name of the widespread genusVerrucaria. Its different species colonize siliceous and carbonatic substratesand fast-moving areas of streams, as well as marginal ones barely sprayedby water.Light conditions are very important in the distribution of aquatic lichens.Among the species which can tolerate reduced light are Verrucaria hydrelaand Porina chlorotica. Toleration to drought varies according to species.Some (e.g., Verrucaria funckii) cannot withstand even short periods of sub-aerial exposure. Others are sensitive to prolonged submersion (e.g., Derma-tocarpon luridum, which colonizes areas that are submerged only duringfloods).The result is vertical zonation of species with respect to low and high water,which becomes particularly evident on rocks with large homogeneous sur-faces which are partly bathed by water. This kind of vertical distribution is alsotypical of aquatic and hygrophilous mosses and will be discussed later. Somelichen form typical associations with species of moss and hepaticas in smallstreams at medium altitudes, especially on siliceous substrates. Analysis ofthese associations provides useful information about the quality and integrityof such mountain streams.

3938

A lichen of the genus Verrucaria

J F M A M J J A S O N D J F M1989 1990

1412108642086420

6420

6

5

4

3

2

1

0

1086420

m3 /

sec

°C

Phormidium autumnale

Chamaesiphon geitleri

Hydrurus foetidus

Seasonal variations in the surface cover ofsome algal species, corresponding to variationsin discharge (m3/s) and temperature (°C)

In order to survive in these particular environmental conditions, subjected toconsiderable changes over the seasons, higher plants have had to adaptthemselves to both flooding during high water, and drought during periods oflittle or no water. The following paragraphs explain what mechanisms theyexploit.The distinctive and perhaps most fascinating feature of these environmentsis their remarkable dynamism. During high waters, the stream shifts its bed,carries considerable quantities of large-sized material (up to one-third ofthe water volume!), reshapes the course of its channels by submerging oldobstacles and creating new ones, and erodes its banks and the foot ofmountain slopes while depositing coarse material in plain areas.This continual, extreme dynamism contrasts with the need for stability ofman’s villages and his works. People living near watercourses, whether inthe Alps or in the Appennines, have often had to face the consequences ofhydrogeological disorders such as landslides, instability, solid transportand erosion. The vegetation growing on banks outside the area floodedduring high water (alluvial plain), is not especially linked with the water-course (except for some species which reveal the humidity of the under-growth in these areas).

41■ Bryophytes and higher plants

Mountain streams have fast, turbulent waters, undergo intense erosion andare cold - all unfavourable to the development of bryophytes and vascularplants. Although fast-moving waters do limit the growth of mosses andaquatic plants, many species are widespread. Current speed and substratumlithology (the latter influences water chemistry: acid, around neutral or alkalinewaters) are the main factors in determining which plant communities canadapt to life in streams.Vegetation on banks and beds is more highly developed. As water flowundergoes seasonal changes, there may be different types of plant asso-ciations. These parts of stream beds which frequently undergo small varia-tions in water level are colonized by pioneer plants, capable of growing andfructifying rapidly during periods of low water, before later floods submergethe area again.The edges of this vegetation, in areas subjected to seasonal regular (but lessfrequent) variations in water level, is characterized by bushes which can tole-rate flooding, such as willows. In areas which are only flooded occasionally,colonies of bushes and trees make up the riverbank woodland.

40

A typical mountain stream bed In mountain streams, various kinds of vegetation colonize areas which are frequently flooded

Disorders caused by streams, such as erosion at the foot of slopes, may beremedied by planting suitable grasses, shrubs and trees on the banks. Unlike rthe zonal vegetation which, if undisturbed, depends on local climaticconditions and is therefore restricted, the vegetation which is closely linkedwith watercourses depends to a lesser extent on climate and is therefore veryuniform in its essential structure throughout central Europe.Mountain streams in general must be considered as habitats deserving rigo-rous protection. Streams in natural conditions, like those described in thischapter, the flow rates of which vary greatly and are colonized by great quan-tities of bank bushes and trees, are becoming more and more rare. Humanintervention has had a strong impact: besides causing pollution, man hasredesigned the course of streams, constructed artificial banks, or loweredtheir beds by excavating sand and gravel from them.Many specialized plants can no longer survive in such revolutionized environ-ments. In natural conditions, the bank vegetation of a mountain stream car-ries out essential functions: it offers food and shelter to the local fauna, con-tributes to the removal of nutritive salts (nitrates and phosphates) which flowinto the stream from the catchment basin, and reinforces banks.The valleys of watercourses are also important channels for the diffusion ofplants belonging to different vegetational and floristic areas.

4342

Bank vegetation

Comparison between natural and semi-artificial stream environments

Bryophytes are systematically placedbetween algae and vascular plants(pterydophytes and higher plants) andinclude liverworts and mosses. Liver-worts - the most primitive group - mayhave either a thallose form with alobed structure, or a foliated form withstalks and leaves without ribbing, as inScapania undulata.The delicate morphology of aquaticliverworts makes them vulnerable tofast-moving water and the material itcarries. Unlike liverworts, mosses have a morecomplex structure, with clearly diffe-rentiated leaves and stalks, more sim-ilar to that of vascular plants. How-ever, aquatic mosses living in runningwater also have to be considerablyflexible and traction-resistant, as an efficient anchoring system may be fun-damental for their survival.Some species (e.g., Fontinalis antipyretica) carpet pebbles thickly by adheringto them with their primitive rhizoids. The leaves of aquatic mosses are oftendense and unilaterally arranged. Stalks and branches are elongated and thetips of leaves are small, with reinforced ribbing. Mosses are very sensitive todrought, but few bryophytes grow directly in water: most of them prefer onlyperiodically wet or submerged areas.Bryophytes have also adapted to the typically low temperatures of mountainstreams. Their photosynthesis requires free carbon dioxide, which is dissolvedin higher quantities in cold waters. Recent studies show that the photosyn-thetic rate of mosses adapted to life in cold streams decreases with increasingwater temperature. The type of substratum is essential in determining the presence of manyspecies of bryophytes in streams. Thus, the genus Cratoneuron is only foundon calcareous substrates and Scapania undulata on siliceous ones.Bryophytes also feature indifferent species, like Brachythecium rivulare. Communities of aquatic mosses are quite homogeneous in Italy and centralEurope. The Italian Alps and Appennines host communities of Platyhypnidiumriparioides (which adheres to rocks, forming sometimes quite large tufts),

45Many factors contribute to this pro-cess: the fact that moving water doesnot only carry seeds and vegetativepropagules, but also whole plants orfragments of them; the reduced com-petitive pressure of alluvial depositsand temporarily flooded areas; the for-mation of new soil during high water;an efficient supply of nutrients andwater which enable sometimes verydemanding plants to develop; and theability of animals living near streamsto transport seeds (essential for thecolonization of upstream areas).

Aquatic flora. There are no vascularplants adapted exclusively to life infast-running waters.Some species, typical of still waters,may also be found in streams, butonly in areas where the water is calm.Their distribution is irregular anddepends on environmental condi-tions, which change with any markedincrease in flow.The reproduction of vascular aquatic

plants is mainly vegetative, since their seeds cannot germinate in running wa-ter. In this case, colonization occurs through fragmentation, i.e., plant partswhich are able to generate new individuals are carried by the current.Instead, the reproduction of bryophytes (mosses and liverworts) depends onwater. Mosses do not reproduce by means of flowers and seeds, but frommale and female gametes born on the protonema. This is a thin, green, pri-mordial filament which forms only when spores germinate. Male gametesneed water - even just a drop of rain or dew - to reach and fecundate femalegametes, from which a new bryophyte will develop. Unlike vascular plants, bryophytes cannot regulate their transpirationprocesses actively, and therefore live in more or less humid environments.They avoid areas with fast-moving waters and prefer calm waters (springs),where they carpet large areas, both submerged and emerging.

44

Liverwort Scapania undulataBryophytes on the calcareous banks of amountain stream. Aquatic bryophytes, such asPlatyhypnidium riparoides ( 1 ) live underwater.Just above the level of mean flow areCratoneuron filicinum ( 2 ) and Dichodontiumpellucidum ( 3 ), followed by Brachytheciumrivulare ( 4 ) and Didymodon spadiceus ( 5 ).Hygrohypnum luridium ( 6 ), Fissidenscristatus ( 7 ) and Ctenidium molluscum ( 8 )are found at maximum flow level. Thalloseliverwort (Conocephalum conicum) ( 9 ) growsin areas which are never splashed by water

after a possible increase in waterlevel. If there is a violent storm, forinstance, the level of the stream mayrise and submerge plants, which arethen carried away by the current, buttheir seeds may start a new life-cycle.In this environment, herbs do not onlyhave to tolerate periods of sub-mersion, but also drought. This is whytheir roots follow the level of theaquifer, or why they reduce theirtranspiration both through the xero-morphic structure of their leaves andtheir own shape, which is similar tothat of dwarf shrubs.This is the case of mountain avens(Dryas octopetala), which forms lowcarpets with creeping woody stalks. Itshorny leaves look like those of oaktrees: they are oblong-elliptical, den-tellated, and up to 3 cm long, withwhite down on their underside. Thisgrass produces single, cup-shaped,creamy-white flowers with upturnedcorollas up to 4 cm wide, with yellowstamens. Its feathery silver fruit isequally beautiful and lasts all summer. Pioneer vegetation alternates with areasof thicker vegetation, made up ofstretches of steppe-like meadows withgrasses like Calamagrostis pseudo-phragmites, typical of Calamagrosti-etum pseudophragmitis, an associa-tion generally found in south-easternEurope.Its erect, leafy culm may reach aheight of 1.5 m, and its undergroundoffshoots enable it to colonize newsandy areas very quickly, even after

4746

Alpine willowherb (Epilobium dodonaei)

Mountain avens (Dryas octopetala)

Alpine toadflax (Linaria alpina)

Mosses may cover most of the rocks on river banks

with its partner species Fontinalis antipyretica and Brachythecium rivulare.The extent of cover may vary considerably, according to the environmentalcharacteristics of specific areas (especially current speed).

Pioneer vegetation of stream beds. When the banks and beds of mountainstreams are frequently submerged even in periods with low water level (ansd soenriched with nutritive substances), we find communities of annual grasses,such as several species of polygons (Polygonum spp.).In natural conditions and in periods of low water, grasses colonize the beds ofstreams. This pioneer vegetation is organized mosaic-wise, as it depends onthe distribution of gravel and sand deposited during periods of high water,according to current speed. Orophilous species like alpine gypsophila (Gypsophila repens), alpine toad-flax (Linaria alpina) and alpine willowherb (Epilobium dodonaei) may also befound in streams. These plants - called in German Alpenschwemmlinge - aretypical of Alpine and sub-Alpine gravelly debris. The seeds of these plantsare carried by currents to alluvial areas, find the proper conditions for theirdevelopment. There they have to germinate, flower and fructify quickly.Rapid, abundant production of seeds guarantees efficient recolonization

recognizable thin, flexible, purple-shaded branches. Its oblong, dark toblue-green leaves, up to 8 cm long,have serrated apexes. Its delicatecatkins appear in early and mid-springbefore the leaves; the males havepurple, then yellow anthers. Alpine tamarisk (Myricaria germanica)is very elegant, with light, glaucousleafy fronds, pale pink flowers, andseeds characterized by tufts of stipi-tate hair. It is sensitive to drought andin the gravelly beds of high mountainstreams, where the level of the watertable varies considerably and is par-ticularly dry in summer, it is replacedby riparian willow (Salix elaeagnos).These are thick, erect shrubs with del-icate, velvety grey shoots. Their linear,whole leaves are up to 20 cm long, grey when young, then dark green anddowny on their underside. Their edges are parallel and revolute with acuteapexes. In spring, delicate, green catkins 3-6 cm long flower with the leaves.The males have yellow anthers.According to changing climatic, geomorphological and pedologicalconditions, these species are associated with more thermophilic shrubs,such as almond leaved willow (Salix triandra), continental forms like darkleaved willow (Salix myrsinifolia), or typically mountainous ones like violetwillow (Salix daphnoides, the Salicetum elaeagno-daphnoidis association,one of the most typical vegetal communities of Alpine valleys and thereforeamong the first to be described). Plants must also withstand drought duringlow water and their roots follow phreatic water.In particular, sea buckthorn (Hippophae rhamnoides) reduces transpirationthrough the xeromorphic structure of its leaves. This shrub has thorny shootsbearing linear grey to green leaves up to 6 cm long, with silvery-bronzescales on both sides. In spring, it produces tiny yellow-green flowers onracemes up to 2 cm long. In female plants, flowers are followed by round,bright orange fruit 8 mm across, particularly rich in vitamin C, which last un-til the following spring. Hippophae rhamnoides colonizes silicic terracesabove high water level, and is particularly lush in south-facing valleys.

49being submerged. It may surfaceagain after being covered by graveland sand.The alluvial plains of streams aretherefore a meeting point for speciescoming from other, different environ-ments, which give rise to very peculiarvegetation.

Areas which undergo seasonalvariations in water level. Areaswhich are less frequently submergedby seasonal variations in water levelare colonized by thickets. Seeds ofwillows and other shrubs may developinto plants of a certain height beforethe next flood.Many species of willows have adap-ted to environmental conditions of

streams and, while submerged, withstand the power of the current by meansof efficient anchoring systems - networks of roots, lanceolate leaves, andconsiderable flexibility of branches and trunks.Frequent floods generally do not only imply accumulation of debris, but alsoability to regenerate: these willows quickly start growing again by developingstrong new shoots from their collet and adventitious roots. High waters may give rise to anaerobic conditions, during which plantsadopt another contrivance aimed at avoiding damage caused to roots byinsufficient oxygen. The possible accumulation of ethanol, a toxic product ofanaerobic respiration, is avoided in many ways. Numerous lenticels in thelower part of the trunk facilitate the diffusion of both oxygen to the roots andof ethanol towards the surface of the trunk. Many species of willows mayproduce non-toxic metabolites like pyruvic and glycolic acids. Streams in the hills and mountains of the Alps and northern Appennines areflanked by pure and mixed willow groves, whose dominant species are purplewillow (Salix purpurea) and riparian willow (Salix elaeagnos).Wet and cool Appennine ravines typically contain Appennine willow (Salixapennina). Purple willow and Alpine tamarisk (Myricaria germanica) are foundin sandy and silty soils which are frequently flooded. Purple willow (Salix purpurea) looks like an expanded shrub, with easily

48

Purple willow (Salix purpurea) Alpine tamarisk (Myricaria germanica)

5150

Willows, of which there are about 300species, usually prefer open areas innorthern temperate regions, althoughthey may be found all over the world,except in Australia. High-altitude, borealregions, are colonized by strong andcold-resistant shrubby types, whichgrow tree-high in milder climates. Alarge number of species live on fluvial,alluvial and open soils. As willows growrapidly and develop strong new shootsfrom its collets, many species are usedto consolidate stream and river banks orhighly eroded mountain flanks. Willows growing in dry environmentshave ovate leaves, which are lanceolatein species colonizing stream banks.The shape of their leaves and theconsiderable flexibility of their branchesand trunks allow willows to bend withthe current during floods, so that theyavoid being broken or uprooted. In the past, the great flexibility of thetwigs of almond leaved willow (Salixtriandra) and purple willow (Salixpurpurea) lent themselves to manyforms of wickerwork.In late winter, the small flowers of willowappear before or at the same time asthe leaves. Flowers do not have petalsand are borne in female and malecatkins on different trees. Male catkinsare usually more conspicuous thanfemale ones, and their pollen is carriedby the wind. Willows also haveimportant melliferous (honey-producing)species which produce nectar in earlyspring, when other flowers are rare.Small seeds develop in female capsulesand are carried by the wind. They arepermeable, and germinate immediatelywhen the climate and season arefavourable. This enables willow tocolonize broad areas with surface

watertables, but it has fatalconsequences when seeds fall in shadyareas or insufficiently damp soils,because the small plants dieimmediately. In the past, the cultivationof willows was important, especially inthe Po Plain, where various specieswere grown to produce fuel for bakeries,

and were also used for basketwork,carpentry, tools, etc.. Wickerwork wasnot restricted to the production ofbaskets, but included other productssuch as fish traps, supports for vinesand other woody plants which grow onespaliers, and strings to tie and fix thethatched roofs of country cottages.

It is also worth remembering thepharmaceutical use of the glycosidesalicin as an efficient febrifuge (anti-fever agent). This substance isextracted from the bark of almost allwillow species, from which salicylic acid(now a component of aspirin) wasobtained in the past.

Willows Karin Ortler

Riparian willow (Salix elaeagnos)

Leaves of riparian willow (Salix elaeagnos)

Purple willow (Salix purpurea) Purple willow (Salix purpurea) White willow (Salix alba) White willow (Salix alba)

Morphological adaptations to currents of leaves of various types of willows. From left to right: whitewillow (Salix alba), crack willow (Salix fragilis), laurel or bay willow (Salix pentandra),almond leavedwillow (Salix triandra discolor and Salix triandra triandra), common osier (Salix viminalis), Europeanviolet willow (Salix daphnoides), riparian willow (Salix elaeagnos), purple willow (Salix purpurea)

In Italy, there are four spontaneousspecies of alder: grey alder (Alnusincana), found in alluvial soils ofcentral-northern Italy; black alder(Alnus glutinosa, see photo), whichcolonizes river and stream banks andbrackish woodland; green alder (Alnusviridis), typical of the Alps, usuallycovered with snow, where avalanchesare frequent; and Italian alder (Alnuscordata), which lives in mountainwoodland in southern Italian regions. Alder is suited to very damp soils andperhaps this is why many botanistsbelieve that the Latin word Alnusderives from the Celtic “al lan”,meaning “living near banks”. Sinceblack alder wood hardens ifsubmerged for lengthy periods, it wascommonly used for piles and otherhydraulic works.Alder wood turns deep orange whenfreshly cut, and was thus endowedwith symbolic meanings, e.g., the treeof life after death.Black alder may be higher than 30 m,round or pyramidal in shape and verystrong, with easily recognizableleaves. The oval, round leaves areirregularly serrated and without aproper apex, which is usually gentlylobed. The upperside is a dark, glossygreen; the underside is a lighter, mattgreen with rusty tufts of hairs wherethe main veins branch.Grey alder, which grows to 10-15 m,is recognizable by its dark grey bark.Its oval leaves are up to 10 cm longand 5 cm wide, doubly serrated alongthe margins, with sharp apexes. Theupperside is dark green and theunderside grey and downy. Female and male flowers are born onseparate catkins on the same tree,

and form in late winter or early spring,before the leaves open. Male catkinsare about 10 cm long and hang ingroups from the tips of branches.Their pollen is carried by the wind.Clusters of female catkins, oval andabout 1-2 cm long, produce small,woody, dark brown fruit about 2 cmlong. These woody nutlets stay on thetree throughout the year. Their seedshave a special structure full of air,which enables them to be easilycarried by running water. Winds carrythem for about 30-50 m, and theymay germinate for 12 months.As alder is a pioneering plant, itgrows rapidly during its juvenilestages, but seldom lives for longerthan 100-120 years.Alder wood, which hardens in water,is used for hydraulic constructions. Itis sensitive to exposure to air and isseldom used as fuel or as carpentrymaterial. Its bark is rich in tannin andwas once used for tanning hides.

Alder Karin Ortler 53Areas flooded only during high water. Along mountain streams, bushes arefollowed by grey alder (Alnus incana association: Alnetum incanae, especiallyin the valleys of high-altitude mountains and dominating areas with very littlehumus), is replaced by black alder (Alnus glutinosa) in areas where wintersare milder. These trees may grow where willow groves and Hippophae rham-noides have previously prepared the soil by gradually collecting sand andgravel. Alders have adapted both to occasional high water and insufficientlyaerated wet soil. Lenticels in the lower part of the trunk provide air to superfi-cial, submerged roots. Roots have tubercules which contain bacteria, living insymbiosis with the plant. These absorb nitrogen from the air, compensatingfor the lack of nitrogen in the soil. The combination of certain conditions determines which species colonize par-ticular areas after floods. Alder seeds germinate in the summer, when waterlevels decrease and enable the growth of alder. The seeds of white willow (Sal-ix alba association, Salicetum albae, the vegetal community of alluvial plainswhich flanks the main rivers of the Po Plain and central Italy) and crack willow(Salix fragilis) flower in June, when mountain stream waters are high and areasfor colonization are not yet available.The germination period of these seeds is limited to a few days, and they can-not be carried by water. They find more favourable conditions for their deve-lopment along the lower stretches of watercourses, on sandy and silty soils,

where they form thick riverbankforests. Low winter temperatures alsoplay a fundamental selective role. Pioneer plants and willows whichusually live near streams and prefersunny areas may no longer live in theshady underbrush of alder woods. Thesoils of these habitats, although still atan early evolutionary stage, areenriched in nutritive substances atevery flood.Thus, associations of megaphorbies(term derived from the Frenchmegaphorbiées) are usually found atthe edge of alder woods and glades,e.g., bishop’s weed (Aegopodiumpodagraria) and figwort (Scrophularianodosa).

52

White willow (Salix alba)

Butterbur association (Petasites spp.) Black poplar (Populus nigra)

Poplars belong to the willow family.Their flowers, like those of willows,have hanging male and female catkinsabout 5 cm long (in black poplar) or 10cm long (in white poplar). However,their seeds are larger: the small, greencapsules open to release seeds cov-ered with a white down similar to rawcotton, which are easily carried by thewind. The leaves of black poplar are tri-angular or ovate, about 10 cm long andwide, with glossy uppersides andopaque undersides. The leaves of whitepoplar have 2-5 lobes, and are about 10cm long and 7 cm wide. When ripe, their surface is glossy, and a dense, whitedown covers their underside. Another type of riverbank forest grows alongstreams and is characterized by Scotch pine (Pinus sylvestris). These conifers,together with willows, colonize calcareous, alluvial streams, which are sub-merged for only 1-2 days during exceptional years. Although Scotch pine hasgreat ecological value (it grows in peat-bogs, on dry soils of rocky slopes or onalluvial debris), it cannot withstand floods lasting more than a few days.

55These hygrophilous and nitrophilousplants grow rapidly to over 1 m.Among the flora of the underbrush isostrich fern (Matteuccia struthiopteris),up to 1.5 m high, and butterbur (Peta-sites spp.), whose dense stalks inspring bear round, purple and white,male and female flowers on differentplants. Base heart- or kidney-shapedleaves grow after flowering. Their di-ameter is about 60 cm and they formdense herbaceous communities. Areas which are not subject to floodsare colonized by alder and also by

trees typically found in riverbank forests of hilly areas, like common ash(Fraxinus excelsior), white poplar (Populus alba) and black poplar (Populusnigra). Common ash has pinnate leaves about 30 cm long, with 9-13 small,oblong, ovate leaves, about 10 cm long and 3 cm wide. Its flowers are deli-cate, violet, without petals, and bloom in spring, before the leaves, from al-most black buds. Its winged, hanging fruit is greenish, then light brown, andripens in thick bunches.

54

Black poplar (Populus nigra)Ostrich fern (Matteuccia struthiopteris)

57Invertebrate faunaBRUNO MAIOLINI · VALERIA LENCIONI

Benthic invertebrates are defined as small animals which live close to the sub-stratum for at least a period of their life. Those of larger size (over 1 mm long),are called “macroinvertebrates”, of which insects constitute the most impor-tant part. In mountain streams, orders of dipterans, plectopterans,ephemeropterans and trichopterans prevail. Invertebrates in mountainstreams have to face two life-threatening obstacles: current speed and coldtemperature, which they overcome by contriving extraordinary adaptations.In order to contrast the current, these animals may have flat bodies (likeheptageniid ephemeropterans), strong suckers (blepharicerid dipterans), andcrown-shaped hooks (simuliid dipterans). The current is not only obstacle, butalso produces a constant flow of food downstream, and is a good mean fordispersion. It is far more difficult for invertebrates to adapt to the cold. Many scientistsconsider temperature the main factor determining the ecology and evolution ofaquatic and terrestrial invertebrates (egg-laying and hatching, growth rates,mating, reproductive strategies, activity models, types of food). Invertebratesliving at high altitudes and latitudes have adopted various strategies to over-come the long, cold winters. Snow and ice, drought, wind, cold and little foodare their most feared enemies. Aquatic invertebrates may exploit the currentto move downstream and avoid freezing or drying up, or they may shelter inunderground waters. But they frequently spend winters in the same place:the capacity of these organisms, particularly insects, to survive in these harshenvironments is due to a series of physiological, biochemical, morphological,behavioural and ecological adaptations. Among these is the production ofmelanin, their small size and hairiness, capacity for feeding and mating on theground instead of in flight (they therefore have small or totally absent wings),the building of cocoons, quiescence, diapause, and resistance to cold. Quiescence is a direct, temporary reaction to unfavourable conditions, whichis interrupted as soon as conditions become favourable again. Diapause is adirect reaction to unfavourable conditions which cannot be interrupted untilafter a certain period of time. For aquatic insects, diapause regards eggs andmature larvae, seldom pupae, and almost never adults. Day length (photoperiod)

Stonefly larva

59

is one of the factors which governs the transition between different physiolog-ical states. In Arctic environments, prolonged diapause has been recorded,i.e., organisms may even protract their inactivity for even many years, until en-vironmental conditions are favourable (the life-cycle of some dipterans of thechironomid family may last 6-7 years).Organisms resistant to cold, i.e., able to survive to temperatures below 0°C forlong periods (even many months at -40/-50°C), without damage, apply twostrategies: hibernation and supercooling. Hibernation freezes theirhaemolymph and all their cell fluids except the cell matrix. The temperature atwhich crystals form and the duration of hibernation are controlled by chemicalsubstances, such as polyhydric alcohol, sugars, amino-acids, and complexproteins of high molecular weight called THPs (Thermal Hystereris Proteins),which lower the freezing-point of body fluids by raising their density and, link-ing with water molecules, prevent the formation of ice crystals.

58

Spring “awakening” is usually a quick process, whereby the same substanceswhich enabled hibernation now provide amino-acids and carbon at thaw,when there is still little food in the environment. Hibernating insects die onlywhen exposed to very low temperatures (-30/-50°C) for many months, whenthe temperature drops further (-60/-80°C) even for short periods, or whenfreezing and thawing cycles alternate. Super-cooling, the most typical strategy of aquatic insects, enables them tosurvive when temperatures drop below 0°C (maximum –20°C) for long periods,during which their body fluids remain liquid. The freezing point of these insectsshifts from –5/-10°C (as in most insects) to –20/-25°C, as they may eliminate orreduce substances which favour the formation of ice, and their body fluids takein anti-freeze substances similar to those used by hibernating insects. Glycerolis frequently accumulated as an anti-freeze, and may constitute up to 10-14%of the weight of the animal.

Cold challenges mountain stream invertebrates Currents: obstacles for invertebrates, but also efficient means of transport

found in areas of submerged vegetation.They crawl on the bottom or swim freelyin water among aquatic plants. They aredetrivorous, herbivorous, or evencarnivorous. Tubificids and lumbriculidsare generally found in fine sediment,feeding on bacteria associated with thesediment itself. Tubificids may abound insediments rich in organic debris and aregenerally dominant at depths exceedingone metre. Enchytraeids, which may alsocolonize terrestrial environments, arepresent where waters are rich inoxygen, particles are coarseand currents fast. Among theoligochaetes whichpopulate runningwaters, only naidids,lumbriculids and tubificids arestrictly aquatic families, ofwhich the first two aregenerally found in glacial andnon-glacial reaches above the tree-line.

Hirudineans (leeches). Hirudineans,better known as leeches, are mostlyfreshwater species found in running andstanding waters. They adhere to thesubstratum and move by means ofsuckers, thus requiring environmentswith hard substrates like rocks, stonesor pebbles. The torrential reaches ofrivers are therefore optimal for specieswhich prefer running water.Their presence is limited upstream bytemperature (they cannot reproduce attemperatures below 10-11°C) anddownstream by increased sandy ormuddy substratum.Few species are found in intermediatestretches, like Erpobdella testacea,E. octoculata and Dina lineata, allpreying on other benthic invertebrates

and resistant to moderate organicpollution. Other species (Dina krasensis,Trocheta bykowskii) may live in streamsat low altitudes, even in large numbers.

Mites. Mites (see drawing) are arachnidsa few millimetres long; they abound insoil fauna, particularly in stream beds,where they provide an excellent exampleof adaptive radiation, with tens ofthousands of known species. Only a fewfamilies have adapted to life in

freshwater (water mites). A group offamilies, known as

hydrachnids, countthousands of species infreshwaters, and even

halacarids, a sea taxon, may befound in freshwaters. Mountainsprings and interstitialenvironments are among thefreshwater environments

colonized by the most interesting watermites. In springs, water mites constitutean important part of the so-called crenalfauna, typical of these habitats, whichrequires perennial, clean springs. In theinterstitial environment, i.e., in gravellyand sandy stream beds, species havedevised adaptations for life insubterranean water: they have no eyesand are colourless.The biological cycle of freshwater mitesis extremely complex, being exceptionalright from the beginning: eggs do notoriginate larvae; rather, pre-larvaedevelop inside eggs. The latter turn intolarvae which leave the eggs and becomeparasitic on aquatic insect larvae(especially chironomids), the internalliquids of which (haemolymph) theysuck. Insect larvae are also exploited as“means of transport” which carry larvae

6160

with regard to population density andinfluence on macrobenthic communities,as they are specialized predators.

Molluscs. There are few molluscs inmountain streams, as most freshwaterspecies prefer still or slow-flowingwaters, due to their scarce mobility and

difficulty in finding the right food.A few species constitute an exception,one of which is the pulmonate Ancylusfluviatilis. Middle-shallow reaches featurespecies of the genus Pisidium, smallfreshwater mussels which live in sandyor pebbly substrates.

Oligochaetes. Oligochaetes colonizevarious freshwater environments and arefound in several stream microhabitats:sandy or muddy bottoms, hard, pebblyor gravelly substrates, areas withdeposits of organic debris or submergedvegetation, etc..Small oligochaetes (some naidids, forexample), may also colonize interstitialenvironments. Naidids are frequently

Triclads. Triclads, or planarians, arecharacteristically found in cool,mountain streams rich in oxygen,especially if small and of spring origin.These small animals are easily identifiedby their extremely long and flat bodieswhich remain tenaciously attached to thesubstratum, even in particularly fast-flowing waters.They prey on small invertebrates such asinsect larvae, crustaceans, gastropodsand annelids, but may also feed oncarrion.In the upper course of mountainstreams, the most common species isCrenobia alpina, well adapted to fastwater speeds and low temperatures.Further down, we find Dugesiagonocephala and Polycelis felina.Although fewer than 20 species areknown in Italy, mostly typical of slow-flowing or standing waters, theirpresence in streams may be relevant

Taxonomy of invertebrates Bruno Maiolini · Valeria Lencioni

Ancylus fluviatilis

Planaria

have swollen, prehensile antennuleswhich they use to seize females duringmating.Moss and interstitial species which arefrequently found in high-altitude streamsand springs belong to the harpacticoids(particularly to the genera Attheyella,Bryocamptus, Maraenobiotus,Hypocamptus, Moraria andParastenocaris).Some species are very rare and onlyfound in restricted areas of the Alps andAppennines; others are typically boreo-alpine, distributed in areas includingnorthern Europe and the Alps (seldom inhigher mountains on the Appennines) -traces which reveal their much widerdistribution during glaciations.Cyclopoid copepods prefer downstreamreaches, and many members of thegenera Acanthocyclops, Diacyclops andSpeocyclops are found in interstitialenvironments.Besides copepods, spring and interstitialhabitats typically contain other smallcrustaceans. In karstic springs,ostracods may be locally found in largenumbers. Their body is enveloped in abivalve carapace (ostracod derives fromthe Greek word meaning shell) whichprotects the soft parts of the body andits appendices. They are round or bean-shaped.Ostracods also feature blind anddepigmented interstitialspecies. Among the mostcommon genera in theDolomites (large quantitiesof calcium areindispensable for thedevelopment of theircarapace) are Potamocypris,Pseudocandona, Cypria (see drawing),

and the rarer Cavernocypris andCryptocandona.In interstitial habitats, other taxonomicgroups of crustaceans are onlyoccasionally found, such ascladocerans, widely distributed insurface environments, and exceptionally,the blind depigmented members of theorder Bathynellacea which, althoughlimited to subterranean waters, haverecently been found in the Alps at highaltitudes.Larger crustaceans are more common insome streams, particularly amphipods,which are found in large numbersdownstream. Their biomass makes themone of the most important food sourcesfor fish. They are generally associatedwith middle-shallow stretches and slow-flowing waters. At high altitudes, theyare present only in a few relict sites.Along the Alpine chain, Gammarusfossarum, G. balcanicus andEchinogammarus stammeri are commonspecies. In the Appennines, they arereplaced by Gammarus aff. italicus,Echinogammarus veneris and E. tibaldii.Other crustaceans found in springs andinterstitial habitats are completely blindand depigmented, and belong to thegenus Niphargus, with about 100species in Italy. N. strouhali often lives in

mountain streams and preferselevations exceeding 2000 m

a.s.l.. This genus has recentlybeen found in interstitial

environments at highaltitudes, e.g., in glacial

streams at the foot of theBernina massif (Switzerland).

Other crustaceans colonize low-altitudestreams, and are only exceptionallyfound in mountain stretches.

63to new habitats (phoresis).From this point onwards, the cyclebecomes even more complex anddevelops in three successive steps(protonymph, quiescent; deuteronymph,similar to an adult but with three pairs oflegs, free and predatory; tritonymph,quiescent again).Tritonymphs finally develop into adultswith four pairs of legs, like all arachnids,bodies divided into two parts, front(gnatosome, bearing mouth parts) andrear (idiosome, bearing legs). The bodysurface is covered with bristles andglands, which probably emit anunpleasant smell and protect watermites from predators.All water mites prey on other aquaticinvertebrates and are very sensitive towater quality. Italian springs and streamsare colonized by many genera andspecies, the most common of which areLebertia, Hydrovolzia, Partnunia,Sperchon and Thyas. The phoretic or transport stage of theirlife-cycle explains why endemic speciesof mites are so rare; most aquaticspecies are widely distributed and maybe found randomly almost everywhere inthe Alps and Appennines.

Crustaceans. In mountain streams,most crustaceans are less than 1 mmlong, and belong to the so-called“meiofauna”. These organisms live onthe bottom of slow-flowingwatercourses, in close contact with thesubstratum (epibenthic) or inside it,between gravel and sand granules(interstitial fauna), even at considerabledepths.Copepods are undoubtedly the mostnumerous crustaceans in springs and

Alpine streams; they are absolutely themost common organisms of our planet,and have colonized all habitatscontaining water (seas and oceans,lakes, ponds, marshes, rivers andstreams, even tiny pools in tree-trunks,mosses and wet soil, caves, interstitialwaters, and even the small lakes whichform in favourable conditions inHimalayan glaciers at 5000 m a.s.l.).These crustaceans have unmistakablefeatures: they have only one eye(Cyclops is one of the most commongenera) and their bodies have two longantennules and two short antennae, withfive pairs of legs (the term copepodderives from the Greek meaning “oar-feet”) ending in a pair of caudal ramibearing long bristles.The female bears one or two egg-sacs;the eggs hatch to become larvae(nauplia), which are very different fromthe adults and, after a number of moults(generally five) they turn into sub-adults(copepodids), which do not reproduce.After five further juvenile stages,copepods become adults after thesixth moult.Sexes are easy to determine becausemost male copepods in Italian streams

62

Harpacticoid copepods (Bryocamptustatrensis) mating

6564 common in streams and has greatecological value, being found in bothpolluted and unpolluted downstreamstretches.A third group of nymphs has adapted tocrawling on the bottom (herpophiles) andincludes the caenid, leptophlebiid andephemerellid families. These mayflies aregenerally associated with slow-movingwaters rich in organic sediments, butmay locally abound at middle-lowaltitudes.There are also burrowing nymphs(oryctophiles), belonging to theephemerid and polymitarcid families,with modified mandibular processes andforefeet which enable them to digtunnels in river and stream bottoms.A few live in stream stretches, as theyprefer slow-flowing waters.The only exception is Ephemera danica,locally abundant, inhabiting gravel andsand streams.

Among these, freshwater crayfish(Austropotamobius pallipes fulcisianus)are widely distributed. They belong tothe decapod order and prefer clean,well-oxygenated stretches at lowelevations, but in particular conditions(Trentino), they may be found at 1500 ma.s.l. Crayfish are common in northernItaly and colonize the Appennines downto the Basilicata region, decreasing innumber southwards. In the past, theywere much more numerous and widelydistributed, but were harvestedindiscriminately for long periods, sincethey are delicious to eat. In recent years,their numbers have fallen still further,partly owing to their sensitivity toworsened water quality. Today, manyregional laws forbid them to be taken,and they are further protected by theHabitat Directive of the EuropeanCommunity.

Ephemeropterans (mayflies).Ephemeropterans owe their name to theshort span of their adult life (in Greek,ephemeros = lasting one day, and pteron= wing). The masticatory apparatus ofadults does not often function and theycan only live as long as their store ofenergy, accumulated during their aquatic

larval stage, lasts. They are found inlakes, marshes and ponds, but alsorunning waters, preferably at middle-lowaltitudes. Many species toleratemoderate organic pollution, andconsiderable numbers may therefore befound in quite poor-qualitywatercourses. In Italy, 94 out of 300European species are found.Mayflies are considered a primitive order,similar to odonates, with a hemi-metabolous development.The ecological role of mayflies inmountain streams is one of considerableimportance and, if conditions arefavourable, they may prevail over themacrobenthic community, both innumber of individuals and total biomass.Most nymphs are herbivores and are animportant source of food for otheraquatic invertebrates and fish.After emergence, they become the preyof many birds, bats and fish which catchthem during the delicate stage ofmetamorphosis, often on the watersurface. Fishermen are aware of this,and adult mayflies are the most imitatedin the refined art of artificial baitconstruction.Mayflies occour in various fluvialmicrohabitats and resort to peculiarmorpho-physiological adaptations.Four genera belong to the heptageniids(Epeorus, Rhithrogena, Ecdyonurus andHeptagenia) and, as nymphs, sharedorso-ventral flattening. Theirhydrodynamic aspect, with flattenedhead, abdomen and legs, is enhancedby the shape and position of abdominalgills, used as efficient suckers toincrease their adherence to thesubstratum. Thus, nymphs can toleratestrong currents by remaining in the thin

Mayfly nymph of the genus Baetis

Subimago of a mayfly of the genus Baetis

Freshwater crayfish (Austropotamobius pallipesfulcisianus)

layer close to the substratum wherewater flow is slow. The most commonspecies found in high-altitude stretchesbelong to this family: Epeorus alpicola,E. sylvicola, Rhithrogena loyolaea,R. alpestris and Ecdyonorus helveticus.The only Italian species of theoligoneuriid family - Oligoneuriellarhenana - has characteristics similar tothose of the heptageniids, and lives infast-flowing Alpine and Appenninestreams.The nymphs of these two families aregenerally flat-bodied, and are also calledlithophilous, as they live on the surfaceof stones and submerged rocks.A second group (hyponeophiles) offamilies includes water nymphs, whosetapering, hydrodynamic body has threestrong, fringed caudal filaments, used asefficient rudders or oars.Baetids and siphlonurids belong to thisgroup, the latter represented in Italy byonly one species. They are typicallyfound in lakes and slow-moving waters.The many species of the large family ofbaetids usually live in the middle-lowstretches of mountain streams. Some,like Baetis alpinus, which is found inmany Italian regions, may colonizeupstream reaches. B. rhodani is also

6766

Odonates (dragonflies anddamselflies). Dragonflies anddamselflies are the largest insects withlarval stages (up to 6 cm long). Theadults are excellent fliers and may beseen far from the point of theiremergence from the water.They then colonize many aquaticenvironments including standing orslow-flowing waters.A few species live in stretches or poolsat the edge of streams, rich in aquaticvegetation.Nymphs, like adults, prey on otherinvertebrates and vertebrates, especiallytadpoles and fry which they catch withtheir typical buccal apparatus, calledmask. This looks like a pair of pincers,which are kept folded when at rest andsnap forward to grasp the prey.Therefore, their method of hunting is bystalking, during which motionlessnymphs mimic aquatic vegetation.

This order is divided into two groups,zygopterans or damselflies, andanisopterans or dragonflies. In theformer group, only one genus livesexclusively in running waters,Calopteryx, with three Italian species(C. virgo, C. splendens and C.haemorrhoidalis) found at middle-lowaltitudes. The latter group includes twofamilies with species adapted to runningwater, cordulegastrids and gomphids.The former has only one Italian genus(Cordulegaster), which includes a fewvery large species, whose larval stageoccurs in slower areas of streams.Gomphid nymphs are flatter andstumpier, and live in the mud and gravelof mountain stream beds.

Plecopterans (stoneflies).Plecopterans, or stoneflies, derive theirname from the Greek pleco = fold, andpteros = wing, due to the typical positionin which adults keep their wings at rest,folding them scissorswise to cover theirabdomen. This is probably the mosttypical order of benthic fauna inmountain streams, since many speciesare particularly suited to cold, well-oxygenated, clean and fast waters.This, and downstream pollution of rivers,confines stoneflies to streams ataltitudes over 600-700 m. Their distribution is not only limited bytheir strict ecological requirements(stenoecious nature), but also by thepoor flying skills of the adults.Over 3000 species are known in theworld, 400 of which belong toEuropean fauna. In Italy, 144 species areknown, divided into 21 genera groupedin 7 families.One peculiarity of stoneflies is their use

of sound signals, which are produced bydrumming the substratum with theirabdomen. This phenomenon has beenthoroughly studied, and the recordingand analysis of sounds reveal that theseare true languages.The rhythm of beats and the frequencyof sequence repetition differ betweenspecies and sexes. In some cases, even“dialects” have been recorded inpopulations of the same species butgeographically apart. Stoneflies of the northern hemisphere(Palaearctic and Neartic) are divided intotwo large groups: Systellognatha andEuholognatha. The buccal apparatus ofadults of the former group does not

function, making it impossible for themto feed. Nymphs are generallyomnivorous and good predators in thelast stages of their development.Euholognatha include species whichfeed as adults, meaning that they maylead a subaerial life for some weeks.Both adults and nymphs arephytophagous or detritivorous and feedon algae, mosses and vegetal debris.Their development is hemi-metabolicand their larval stage lasts for about oneyear, although biennial cycles are known,

e.g., in Dinocras cephalotes. A large number of moults is necessary toachieve the adult stage, rangingbetween 10 and 20, with a maximum of33 in Dinocras cephalotes, the largestspecies, the winged females of whichare over 30 mm long. When mature,nymphs leave the water and have theirlast moult, to become adult insects.This generally occurs in spring, but thereare many known cases of winteremergence from the water, with flyingadults which mate on snowy shores.There is usually only one generation ayear (univoltine species), but infavourable conditions, a secondautumnal generation may follow the first(bivoltine species), e.g., Nemurellapictetii. Nymphs generally look like mayflies, buthave only two caudal cerci and lack leaf-like abdominal gills.Nymphs of stoneflies, although typical ofmountain streams, are not particularlysuited to life in water, and colonizemicrohabitats characterized by slowcurrents, like leaf debris, the lower partsof stones and rocks, and the quietwaters of pools. Stoneflies are widely distributed in allmountain streams and, in favourableconditions, constitute more than 50% ofthe macrobenthic population. Afterdipterans, they are the group mostfrequently found in high-altitudestreams, even with large species, likeDictyogenus fontium, populations ofwhich have been found in the Alps atelevations over 2800 m a.s.l.Other smaller species living upstream(rheophilous-orophilous species) areProtonemura ausonia, P. caprai,P. elisabethae, P. brevistyla, Nemoura

Cordulegaster bidentatus

Stonefly nymph of the genus Perla

6968 (Helophoridae). The former have fringesof swimming hairs on their legs, and thelatter have strong claws to cling to thesubstratum. Aquatic adults have trachealrespiratory systems like those ofterrestrial species, and have contrivedadaptations to store air for their quitelong immersions. Diving beetles, waterscavengers, crawling water beetles, andminute moss beetles sometimes emergeto store air. They adopt differentpositions in order to store oxygen.Diving and crawling water beetles, forexample, stand on their heads, obliquely,until the rear part of their body touchesthe air-water interface. They thencapture an air bubble, which they tuck inthe chamber under their wing surface,i.e., in the cavity between abdomen andelytrum. Exhaled gases are released asbubbles. Instead, water scavengers,minute moss beetles (see drawing) tilttheir bodies upwards and conveyair to the chamber under theirwing surface through theirantennae. Minute mossbeetles are aquatic only asadults, whereas marshbeetles (Helodidae) areaquatic only as larvae.Larvae and adult beetles eatvarious kinds of food. Amongadult water beetles, divingbeetles are predators, waterscavengers are omnivorous,and the other families aregenerally herbivorous.Larvae of diving and waterscavenger beetles are predators,larvae of crawling water beetlesare herbivorous suckers and the otherfamilies are herbivorous/detritivorous.Aquatic beetles prefer river bank

environments characterized by slow,shallow waters, rich in vegetation andorganic matter. This is why they are notfound in upstream stretches, where fast-flowing water, stream bed instability andsevere erosion make colonizationdifficult. They may live at higher altitudesin perifluvial wet areas, the ecologicalrole of which is that of “refuge areas”where environmental conditions are notso extreme.

Dipterans. The order of dipteransincludes the highest number of speciesin the class of insects. With the soleexception of oceans, dipterans colonizealmost all environments during thedifferent stages of their life-cycle. Theyinclude more than half of all aquaticinsects and, in the larval stage, live in alarge number of environments - streams,lakes, ponds and marshes. Their

development is complete, withterrestrial or aquatic larval stagesand subaerial adult stages. Some

species are semi-aquaticand live in wet soil, rotting

hollows in plants or animalcarcasses. Larvae of dipterans

feature all nutrition models,including plant feeders, detritusfeeders and predators.

The name of these animals,“with two wings”, derives fromthe fact that adults have only

one pair of front wings, sincethe rear ones are transformed intoequalizers (appendices with aclub shape) which are used asflight stabilizers.

According to the shape of the antennaein adults, dipterans are divided into twosub-orders, nematocerans and

mortoni, N. obtuse, Leuctra rosinae,L. festai, L. teriolensis, Isoperla rivulorum,Perlodes intricatus, Siphonoperlamontana and Chloroperla susemicheli. At middle altitudes, there are mediumand large species like Perla grandis,Dinocras cephalotes, D. ferreri,Dictyogenus ventralis, Perlodes intricatusand Isoperla rivulorum. The genus Tyrrhenoleuctra, with only oneItalian species - T. zavattarii - deservesspecial mention. It is found in Sardinianand Corsican streams.

Heteropterans (bugs). Bugs arecommonly found in aquaticenvironments, in both larval and adultstages. Their name derives from theirtwo “different wings” (hetero = different;pteros = wing), i.e., partially sclerotizedfront wings and totally membranaceousrear wings. Nymphs are very similar towinged adults, and turn into adults by

means of gradual transformations inshape and size called paurometabolousmetamorphosis. Aquatic bugs preferquiet waters, although many species arefound in running waters, near shores, inpools, in calm river sides, and generallywhere water current is slow.Some bugs called gerrids live on thewater surface, and others, nepids, liveunderwater. The former walk or skate onwater surface exploiting the superficialtension, the latter walk on the bottom orswim in the vegetation. Most of themprey on other insects, such as mites andspiders. Larger species suck tadpoles,fry and the eggs of amphibians and fish.Smaller species are omnivorous and alsofeed on benthic meiofauna, microscopicalgae and organic debris.Among the most common genera instreams are Gerris, Aquarius and Velia.Aquarius najas lives exclusively instreams, in calm stretches and pools.

Coleopterans (beetles). Beetlesrepresent the largest animal order, withat least 350,000 species, 10,000 ofwhich belong to Italian fauna. Somefamilies are found both in standing andrunning waters. They are the onlyholometabolous insects which live inaquatic environments as both larvae andadults. Adult water beetles can alwaysfly and seek better environmentalconditions. There are two categories:swimmers, such as diving beetles(Dytiscidae), crawling water beetles(Haliplidae) and water scavenger beetles(Hydrophilidae), and walkers,represented by long-toed water beetles(Dryopidae), riffle beetles (Elmidae),minute moss beetles (Hydraenidae) andanother family of crawling water beetles

Adult stonefly of the genus Chloroperla

7170 Among brachycerans are houseflies(Anthomiidae or Muscidae), snipe flies(Athericidae), long-legged flies(Dolichopodidae), dance flies(Empididae), and soldier flies(Stratiomyidae). Non-biting midges andblack flies are the largest groups inhigh-altitude streams, and the only onespresent, apart from a few exceptions, inglacial streams. Proceedingdownstream, we find dance flies andcrane flies and, still further down,solitary midges, net-winged midges andsnipe flies.Chironomids (non-biting midges).The family of chironomids is the largestin freshwater environments, both fornumber of species and individuals.About 15,000 species are known in theworld, 400 of which are found in Italy.They are divided into 8 subfamilies, 5 ofwhich live in Italy: Tanypodinae,Diamesinae, Prodiamesinae,Orthocladiinae and Chironominae.Adults live in an aerial environment but,as larvae, they colonize variousfreshwater environments, such as lakesand mountain streams, rivers, ponds andpools, clean waters rich in oxygen aswell as very polluted ones, both poor(oligotrophic) and rich in nutrients(eutrophic). Some species colonize seawater, particularly areas between lowand high tide, and others live on land.Thus, non-biting midges are a definitelycosmopolitan group of insects.They include many species of highecological amplitude (euryecious), butalso stenoecious ones, i.e., they areunable to live in conditions different fromthose to which they have becomeadapted. Therefore, they are goodbiological indicators as they reveal even

minimal variations in the environmentalconditions in which they live.For example, the presence ofDiamesinae larvae in watercourses, andparticularly species of the genusDiamesa, such as D. steinboecki,indicates “glacial” conditions, as theyare typical of these environments.In mountain streams, non-biting midgesare certainly the largest group ofdipterans, both in terms of number ofindividuals and species.At high altitudes and in extremeenvironments, like the upstreamstretches of mountain streams,chironomids are usually the onlyinvertebrates. A clear longitudinalsuccession is not only evident inspecies, but also in subfamilies.In upstream stretches, where waters arecool and well-oxygenated, Diamesinaeand Orthocladiinae abound. These twosubfamilies include several rheophilousand cold stenothermal species, i.e.,adapted to life in the fast-flowing, cloudyand always cold waters of glacialstreams. In particular, larvae of Diamesaspp. have contrived several adaptations

rigid envelopes, in the water or on thesoil. Adults generally live for about onemonth, during which mating (in flight, onvegetation, the ground or even in water),and egg-laying occur. Dipterans includevarious haematophagous adult specieswhich attack humans and other warm-blooded vertebrates (ceratopogonids,culicids and simuliids are known for theirirritating bites), and they may also carrydiseases.Although the order features manydifferent forms, single families arecharacterized by uniformity of shape.Nematocerans have completelysclerotized and evaginated heads(cephalic capsules), which are thereforeclearly visible (eucephalous larvae), orsmall, only partially sclerotized heads,set deep in the thorax (hemicephalouslarvae). Larvae of brachyceran speciesare, with rare exceptions, hemicephalousor acephalous, i.e., their heads are verysmall, with few sclerotized parts, andpartially or completely set inside thethorax.Body segmentation is usually evident,but thoracic and abdominal areas arenot clearly distinguished.The larvae of many dipterans,particularly those with aquatic juvenilestages, are little known, and it is oftennecessary to breed them to their adultstage to identify the species.The most numerous families ofnematocerans in mountain streams arenet-winged midges (Blephariceridae),biting midges (Ceratopogonidae),non-biting midges (Chironomidae), dixidmidges (Dixidae), moth flies(Psychodidae), blackflies (Simuliidae),solitary midges (Thaumaleidae) andcraneflies (Tipulidae and Limonidae).

Larvae of non-biting midges (Chironomidae) Larvae of midges (Diamesa, Chironomidae)

brachycerans. The former have longmoniliform antennae made up of manyjoints, a slender body like that ofmosquitoes and long, thin legs.Brachycerans are characterized by shortantennae and a stocky aspect, like flies.Dipterans include a large variety of formsand adaptations, and may colonizehighly polluted or environments whichare “inhospitable” for most insects, likewastewater, sulphurous and thermalwaters and cold glacial streams.This is due to the ability of larvae totolerate low concentrations of dissolvedoxygen, owing to oxygen storageinduced by respiratory pigments similarto haemoglobin (e.g., Chironomus of thegroup thummi), or anaerobic respiration(i.e., without oxygen).Larvae are sub-cylindrical, thin andworm-shaped, or fleshy and stocky(dorso-ventral flattened shapes are rare),and are characterized by jointless legs.They may have pseudopods (false legs)in various positions, with or withouthooks, spiracles, tubes or respiratoryfilaments. During the pupal stage,individuals may be free or enclosed in

7372 feathery in males. Their thin body lookslike that of mosquitoes, but chironomidshave a humped thorax which partiallyshields their head, and sucking mouthparts instead of biting ones.This is why chironomids are known as“non-biting midges”.Their long legs shake in a typical wayduring flight, so that they appear to be“gesticulating” (their name comes fromthe Greek chironomeo = to gesticulate).Females lay eggs on the water surfaceor near the shore, gathering them ingelatinous masses which may be free orattached to the substratum.The new-born larvae moult 4 or 5 timesbefore metamorphosis. Emergence mayoccur in spring, summer and/or autumn.

Adult life is short and there is only timeto mate and lay eggs.As regards altitudinal distribution ofchironomids in streams, higherstretches, where water temperature insummer never exceeds 3-4°C, aredominated by the subfamily ofDiamesinae with the genus Diamesa,represented by species like Diamesasteinboecki, D. latitarsis,D. goetghebueri, D. bertrami andD. zernyi. Another Diamesinae found inupstream stretches, and sometimes themost frequent (in non-glacial streams) isPseudokiefferiella parva. In the samestretches, Pseudodiamesa branickii mayalso be found, particularly betweenmosses and algae. Together with

to fast currents and unstable substrates,like a) long and strong claws with whichto cling to the bottom; b) elongated rearpseudopods to cling to larger stones andincrease the stability of larvae; c)construction of sand “tubes” cementedwith saliva to protect themselves fromthe current. Besides these strategies,many of them colonize small depressionsin pebble surfaces, to avoid beingcrushed by stones rolling in the streambed. These species feed on organicmatter originally carried by the wind(spores, pollen, vegetal fragments, deadinsects), which is trapped in ice andreleased in stream water during the thaw. The length of chironomid larvae rangesfrom 2-30 mm and their colour from greyto dark yellow, violet, orange, red andgreen. Some species of theChironominae subfamily(e.g., Chironomus of the thummi group),are typically red: these are the ordinary“bloodworms” on which aquarium fishoften feed. In nature, they live in waterscharacterized by high organic pollution.Their blood-red colour is due to thepresence in their haemolymph of arespiratory pigment very similar tohuman haemoglobin, which enablesthem to survive even in poorlyoxygenated environments. All larvae areworm-shaped, i.e., have elongated,segmented bodies, often covered withbristles and without real legs.They only have two pairs of hooked“pseudolegs”, front and rear, with whichthey cling to the substratum.The lives and even the shapes ofchironomid larvae are considerablydetermined by their feeding habits.Some larvae are herbivorous and scratchthe algal and bacterial cover of the

substrates they colonize; others aredetrivorous and collect particles oforganic debris from the bottom; and yetothers are carnivorous and prey on smallanimals. These generally belong to theTanypodinae subfamily. Predatory larvaehave contrived various adaptations tothis kind of life: a barely sclerotized chin,in order to swallow prey whole,scythe-shaped jaws like pincers, a large,sclerotized tongue which rollsbackwards to push the prey down thepharynx, retractile antennae onhydrodynamic heads, and greatlyelongated pseudopods to move quicklyand jerkily.In other subfamilies, sclerotized chinsand oblique-moving jaws scratch algaeand debris off submerged surfaces.Non-biting midges living on thesandy-muddy bottoms of lakes generallyproduce tubes, in which the larvaecreate currents of water by waving theirbodies to and fro. This movementconveys food particles (algae, bacteria,etc.) to a specially constructed net,which is produced with their own salivaand lies on the bottom.Periodically, the larvae swallow this netand replace it with a new one.Some species burrow thin tunnels in thesubmerged leaves of aquatic plants.Others are symbionts or parasites ofother invertebrates.Pupae and larvae have similar sizes andcolours, but the front part of their bodyis swollen with the cases of adultantennae, legs and wings. Pupae mayswim freely or, for those species living intubes, remain partially enclosed in thelarval tube itself. The length of adultsranges from less than 1 to about 14 mmand they have very long antennae,

Sketch representing the life-cycle of non-biting midges (chironomid dipterans): eggs ( 1 ); larva ( 2 );pupa ( 3 ); adult or imago (male 4� and female 4� )

7574

current is faster and more water can befiltered. The silk glands are also usedwhen moving downstream. In this case,the larvae stick silt to the substratumand quickly spin a “safety rope”, holdingon to it until they reach the desiredposition. This original system enablesthe larvae of black flies to occupy evensmooth surfaces of rocks exposed to thecurrent, where few invertebrates canresist. Thus, they may avoid competitionfor space and the danger of beingpreyed upon. In stream beds withmacrophytic vegetation, these larvaeadhere to various plant parts, and asingle emerging grass stem may host upto 200-300 of them. The larvae have 6-9instars until they build a triangularenvelope in which they begin theirmetamorphosis. In the Prosimuliinaesubfamily, the envelope is very small andits shape is not well-defined. Adults look like small, humped flies, witha “flattened” nose (from which theirname derives), and the females of manyspecies are haematophagous (blood-suckers). A “blood meal” is needed totake on organic iron to ripen eggs.

Very restrictive conditions govern whichhost’s blood is sucked and thus somespecies attack birds (subgeneraEusimulium, Nevermannia), horses(subgenus Wilhemia) or bovines(Prosimulium latimucro, P. rufipes,Simulium ornatum, S. intermedium,S. variegatum, S. paramorsitans).If cattle are severely attacked, an intenseanaphylactic reaction may even kill theanimals, and in Alpine areas there havebeen cases of murrain since the early1970s. As attacks occur during the dayand never in closed areas, seriousdamage may be avoided by quicklyproviding shelter. Humans may also bebitten, generally with no complicationsexcept for those who suffer from allergicreactions. The development of larval groups ofblack flies is helped by slightly increasedorganic pollution, and consequent largernumbers of bacteria and organicparticles in the water. High levels ofpollution limit the presence of these flies,because smooth surfaces are coveredwith bacterial and periphytic covers. The altitudinal distribution of species is

Diamesinae, there may also beOrthocladiinae, such as Orthocladiusrivicola gr., O. frigidus, Eukiefferiellaminor/fittkaui, E. claripennis gr. andTvetenia calvescens/bavarica.At medium altitudes, Orthocladiinaebecomes the largest subfamily, fornumber of individuals, genera andspecies (Chaetocladius piger gr.,Heleniella ornaticollis, Corynoneura spp.,Thienemanniella partita, etc.).Diamesinae and Orthocladiinae arereplaced downstream byChironominae, particularly Micropsectraatrofasciata gr. Simuliids (blackflies). Together with non-biting midges, blackflies are the firstcolonizers of high-altitude streams,where they may assemble in largenumbers if conditions are favourable.Their larval stage is spent in runningwater, particularly in fast-flowingstretches.

They are a very old group, as shown bya fossil pupa which dates back 160million years, well into the Jurassicperiod. Today, 1500 species are known,400 of which live in Europe and 70 inItaly.The life-style of blackflies is particularlyinteresting at both larval and adultstages. Larvae are typically pear-shaped, with a swollen abdomen.They feed on fine organic particles andbacteria, which are filtered by specialorgans called cephalic or mandibularfans. These derive from thetransformation of labial parts whichevolved into fans, formed of a series oframi, generally between 30 and 50, uponwhich many hairs grow, creating anefficient capturing system. The larvaehave silk glands which produce aviscous liquid with which they adhere tothe bottom, by means also of hooks atthe end of their abdomen and on theirsingle thoracic pseudopod. The twoseries of hooks alternate with newadhering systems, enabling them tomove on smooth surfaces upstream, insearch of micro-habitats where the

Larvae of black flies (simuliid dipterans) The special technique adopted by blackfly larvae to move upstream

Adult specimen of black fly

7776 bacterial or periphytic covers of thesubstratum, usually large, smoothsurfaces washed by fast-flowing water.Pupae, like larvae, live attached to thesubstratum in the same environments,and their size is similar to that of maturelarvae (5-12 mm). The pupae adhere tothe substratum with 3 or 4 suckerslocated ventrally along both sides of theabdomen. Net-winged midges are consideredindicators of good environmental quality,as they are very sensitive to severalforms of pollution. This is not only dueto their physiological intolerance tochemico-physical variations in water, butalso to a series of indirect effects, aboveall reduced adherence to the substratumcaused by the overgrown bacterialcovers, filamentous algae and mosseswhich coat the surfaces of eutrophicenvironments.The poor mobility of the larvae and theirhabit of colonizing the upper part ofstones makes blepharicerids sensitiveto sudden variations in water flow -typically streams which are subjectto hydroelectric regimes.The presence of these animalsindicates good trophic andhydraulic conditions. In Italy, there are 5 genera and13 species, all living infreshwater.Among these, Liponeuracinerascens with its twosubspecies minor andcinerascens,lives at highaltitudes, inthe Alpsand in the ridge between theAppennines and the Maritime Alps.

Athericids (snipe flies). This is a smallfamily of brachycerans, with aquaticlarvae and adults which sometimes suckthe blood of other arthropods ormammals (see drawing). They arefrequently found in streams with low ormoderate quantities of organic matter.The larvae live in calm areas of thestream, burrowing in sand or gravel,under the bark of submerged branches,or on mosses. The females of manyspecies lay eggs in a peculiar way:many of them gather on the branches ofa tree suspended over water, laymasses of eggs, and then die, remainingsuspended from the branch. Later, thelarvae plunge directly into the waterbelow. Three species are usually found instreams: Atherix ibis, Ibisia marginataand Atrichops crassipes.Empidids (dance flies). This is a largefamily, with 270 species known in Italy.It is widely distributed and lives inalmost all environments, including highaltitudes (over 2000 m). The larvae maybe terrestrial, aquatic or semi-aquatic.

In streams, they live among mossesand stones, or on fine, wet sediments

on the bank. Their cephalic capsuleis small and their mandibular

hooks are particularly well-developed. This is due to thefeeding habits of the larvae,which prey on simuliids andchironomids voraciously. Other dipteran families.

Thesefamiliesinclude

species whichlive in peculiar environments, like drainresidues, waste, thermal and sea

relatively predictable, as many speciesare closely linked to their environment(stenoecious).Upstream areas are characterized by theProsimuliinae subfamily and somespecies (Prosimulium latimucro andP. rufipes) may colonize the lowerstretches of Alpine glacial streams, wherethe mean temperature is about 0°C.In Appennine areas live P. albense andP. calabrum, the former extending as faras Sicily, the latter proper to Calabrianstreams. At lower altitudes,besides Prosimuliinae, there isalso the large Simuliinaesubfamily which belongs tothe subgenus Nevermannia,found in both Alps andAppennines, such as Simuliumvernum. Typical Appenninespecies are S. fucense andS. marsicanum. In medium stream stretches,there are many species of thesubgenera Simulium,Eusimulium, Obuchovia andTetisimulium, of which some(Simulium ornatum and S. variegatum)are tolerant or highly tolerant(S. intermedium) of organic pollution. Limoniids (crane flies). Limoniids are adipteran family with many species(about 320 in Italy), most of which arefound in northern regions; larvae areusually terrestrial although a few live instreams. The larvae of some speciestypically live on muddy banks, otherslive in silk tubes covered with debrisbetween emerging plants, and may beherbivorous, detrivorous or carnivorous.The most common genera inhigh-altitude streams are Dicranota,Rhypholophus and Tricyphona.

Thaumaleids (solitary midges). In Italy,there are 14 species belonging to 4genera, of which Thaumalea is the mostcommon in the Alps. The larvae are verysimilar to those of chironomids and mayeasily be confused. They differ for theircephalic capsule, which is slightlyflattened, setose and covered with smalldorsal protuberances. They have onlytwo pseudopods, front abdominal andrear, and a large sclerotized dorsalplaque on each segment of their body.

Thaumaleid larvae are frequentlyfound in mountain streams on rocks

either splashed or covered by athin layer of water (hygropetriclarvae).Blepharicerids (net-wingedflies). Among dipterans, theseare the best suited to life infast-flowing waters, due to thepeculiar and unmistakable“architecture” of their larvae(see drawing). The dorsal part

of their body is made up of aseries of round arches which can

withstand the pressure of the current.Their ventral part has strong suckerswhich enable them to adhere to thesubstratum even under powerfulwaterfalls. Blepharicerids have the mostfunctional and complete suckers of allinsects: they have a real air-pump,made up of powerful muscles.This produces a vacuum, enabling themto adhere to the substratum perfectly.Each adhesive disc has a front slit todetach the sucker and to allowmovement. They have segmentedabdomens and small, conicpseudopods, branchial tufts and lateralappendices.The larvae feed by scratching the

Their development is holometabolousand when metamorphosis approaches,the larvae, which live in mobile cases,climb rocks or similar projections and fixthemselves near the water surface.The front opening closes, and the larva,now a pupa, begins the extraordinaryprocess which will transform it into awinged adult.Long, orderly strings of pupal houses arefrequently seen on submerged rocksalong the water level.Non-case-building trichopteran larvaepupate inside a specially built silk case,fixed under rocks.The poor mobility of most trichopteranlarvae makes them vulnerable to suddenchanges in water flow, and they are oftenmiserably stranded after storms, whenwater retreats.This phenomenon is more frequent instreams subjected to hydroelectricpeaking. Variations in flow are

considerable and sometimes due tonatural causes, as in streams suppliedwith meltwater from glaciers. Therefore,poor mobility, preference for medium-slow-flowing waters, and their prevailingtrophic role as shredders-collectors ofcoarse organic matter (mostly deadleaves) limit the presence oftrichopterans to stretches under trees.However, this does not prevent themfrom colonizing favourable environmentsat elevations exceeding 2500 m a.s.l.Higher stretches are colonized byorophilous and stenothermal species ofcold waters, like Rhyacophila tristis,Philopotamus montanus, Plectronemiaconspersa and Drusus discolor.In downstream stretches live otherspecies of high ecological value, suchas Rhyacophila torrentiumHydropsyche instabilis, Potamophylaxcingulatus and Sericostomapedemontaum.

7978 waters. Among these are mothflies (Psichodidae), bitingmidges (Ceratopogonidae),houseflies (Muscidae) and soldierflies (Stratiomyidae). These familiesgenerally live in areas of streamsrich in organic debris, submergedvegetation or fine sediments (sandand silt).

Trichopterans (caddisflies).Trichopterans derive their namefrom the Greek words trichos (hair)and pteros (wing). Flying adultslook like butterflies with hairy,light-coloured wings. When atrest, the four wings fold roof-liketo cover the animal. More than300 species are known in Italy,divided into 20 families. Adults arecrepuscular or nocturnal, and often fly inlarge swarms in autumn evenings nearwatercourses or lights. The life of thelarvae is particularly interesting, aquaticin both running and standing waters(except for the genus Enoicyla, whichlives on land). The uniqueness oftrichopteran larvae lies in their ability toconstruct variously shaped cases fordifferent purposes. As regards larval shelters, trichopteransmay be divided into three groups: withmobile, fixed, or free cases.Most species belong to the first group.They construct cases around theirbodies to protect themselves and toincrease their resistance to the current.Their constructing technique consists inthe production of a silk-like secretion towhich inorganic (sand, pebbles; seedrawing) or organic materials(mollusc shells, pieces of leaves, stemsor twigs) stick.

The case is conic, with inorganicmaterial in the sericostomatid,odontocerid, and beraeid familiesand with organic or mixedmaterial in the brachycentrid,

lepidostomatid, leptocerid andlimnephilid families.Hydroptilids (microcaddis)make peculiar cases.These tiny species buildseed-like cases made of silkand grains of sand.Goerids insert small stones

next to cylindrical cases, usedas stabilizers to prevent

overturning; the cases ofglossomatids are like camel humps,

with an opening in each apex.The building technique of

trichopterans larvae has even beenadopted by jewellers who breed larvaein aquariums containing grains, sticks,gold leaf and small precious stones ofvarious kinds, to obtain very originaland unique “biological” jewels.The larvae of other families(hydropsychids, polycentropodids,philopotamids) build silk cases not toprotect themselves, but to collect food.These are real “cobwebs” with a conicshape, open to the current, which filter,or rather capture dead or living organicmatter carried by water.These larvae have pygopods with longbristles which form small “brooms”,used to sweep the nets and collect thecatch to eat it. Nets are built understones, rocks, or where water cannotdamage them.Trichopterans also include species(rhyacophilids) the larvae of which donot construct cases, but live free andprey on benthic macroinvertebrates.

Larval case of caddisfly (limnephilid trichopteran) Adult caddisfly

81

■ Fishes

Salmonids of Italian streams. The species which popular beliefimmediately associates with mountain streams is trout. However, thedistribution of this fish is not limited only to this kind of water, but includespedemontane streams, large pre-Alpine lakes of glacial origin and plainstreams. These environments are all characterized by cool or cold water,with tempe-ratures seldom reaching 20°C, usually well below that figure,and therefore, generally well-oxygenated. It is the oxygen requirement oftrout and its very active metabolism which closely link this fish to high-altitude mountain streams, where water turbulence increases the percentageof oxygen to saturation levels. Hydrobiologists classify this stretch as “upperand medium salmonid area”, or simply “trout zone”.As regards fish, trout is therefore the guide-species of these waters, the bestsuited to these ecological conditions, and sometimes the only one present.But trout is an easy definition. Which trout lives in Italian freshwaters? Theanswer to this question is all but obvious, and this issue is the basis ofresearch and discussion for many scientists who still have not come to anagreement. According to Tortonese, whose two volumes in the series “Faunad’Italia”, devoted to bony fish appeared in the early 1970s, all Italian troutbelong to the polymorphic and polytypic species Salmo trutta, characterizedby variable size, skin and behaviour, with local varieties and ecotypes. Thenominal variety Salmo trutta trutta, to which stream or brown (“fario”) troutbelongs, is found in all regions (including Sicily and Sardinia). There are alsotwo endemic subspecies: “marble” trout (Salmo trutta marmoratus), found inthe river Po and its Alpine tributaries, and the Lake Garda trout (Salmo truttacarpio), typical of the largest Italian lake. The “lacustrine” and “Sardinian” or“macrostygma” trout do not have systematic value. Twenty years after Tortonese’s work, Gandolfi and Zerunian proposed a diffe-rent systematic interpretation which, however, they did not consider definitive. Intheir opinion, Lake Garda trout is one species (Salmo carpio) and Lake of PostaFibreno trout (Salmo fibreni) is another. They proposed calling Salmo trutta a

Vertebrate faunaSERGIO PARADISI

Spectacled salamander (Salamandrina terdigitata)