Ecological studies on water plants of 14 sites aroundKangerlussuaq, southern West Greenland, withspecial regard to Potamogeton

Margrit Vöge

Ecological studies on water plants of 14 sites around Kangerlussuaq,southern West Greenland, with special regard to Potamogeton

Margrit Vöge (2002)

AbstractWater plants were studied in 14 lakes and pools around Kangerlussuaq, southern West

Greenland. The study was carried out near the end of seasonal growth in 2000. The sites distinctlyvary in water colour, Secchi depth, conductivity, pH and number of plant species. A total of 18species was observed, representing four life-forms. New to Kangerlussuaq surroundings, twosubmersed species were found: Subularia aquatica and Potamogeton praelongus. Employing sitedata, species and life-forms, plus the species´ demands, four lake groupings/ site types are proposed.Plant zonation is sketched, plant communities, expressed in terms of synusiae and combinations,exhibit eight zonation types. Shoot and leaf morphology of three Potamogeton species are related tothe environment: the internode length appears dependent on light availability or the depth ofsettlement, whereas the high values of leaf length/ leaf width ratio and the large leaf surface area areexplained by the low water temperature. Due to short growing season and low water temperature thePotamogeton shoot complexes appear rudimentary. Some growth-forms reflect particular siteconditions. Spike development is striking in Potamogeton species, but the number of mature seedsat the end of seasonal growth is low. P. filiformis only makes up dense seed banks in lakes withhigh conductivity. Positive correlations and compromises in plant development were recognized.Though nearly all examined plant species developed flowers and/ or fruit, vegetative reproductionand survival appear dominant.

Keywords: Greenland, water plants, Potamogeton, shoot morphology, shoot complexes,leaf morphology, reproduction

Margrit Vöge, Pergamentweg 44b, D-22117 Hamburg, info@solo-tauchen.de

1. Introduction

A lot of work has been done on the flora of Greenland, including water plants (e.g. Böcher 1949,1963). More recent investigations are reported by Fredskild (1992,1996) and Bay (1992). The areaaround Kangerlussuaq is well known for the highest number of lakes in Greenland, with sitesdistinctly varying in several aspects. This makes this region advantageous for ecological studies onplants which additionally experience a short period of seasonal growth. Special attention has to bepaid to vegetative and sexual reproduction, being highly important phases of the life-cycle.Phenotypic plasticity is frequent in Potamogeton. Plants grow by accumulating a varying number offunction-dependent modules. Responses to particular site conditions seem conceivable in a variationof the basic module that is leaf morphology and internode length (1), and of this unity which isspecialized on reproduction that is spike stem and spike length plus the number of fruit (2). Barko etal. (1982) report from laboratory studies leaf and shoot morphology of Potamogeton nodosus to bedependent on water temperature and light. Law (1979) presumes the existence of positivecorrelations between plant features only for such plants, growing in excellent conditions; otherwisecompromises are expected.

1

The aim of the present field study are1. to investigate plant species´ diversity of lakes/ ponds around Kangerlussuaq,2. to examine plant communities and zonation along downward slope,3. to measure module characters of Potamogeton plants,4. to evaluate effects of temperature and light availability5. to recognize correlations or compromises between plant features

2. Materials and methods

2.1. Investigation area and climate

The investigation was carried out in an area of some 50 km ² around Kangerlussuaq (N 67.02°,W 50.69°), between August 19th and September 17th 2000. Lakes and ponds are frequent in thislandscape as a result of a periglacial and impeded drainage. The vegetation in the systems of valleysthat continue to fjord into the ice cap, is very stabilized. Due to the severe dessication, herb fieldrich in species, is totally absent (Böcher 1948). Lowland plant communities are dominated byCalamagrostis lapponica grassland; according to Birks & Penford (1990) variations in aspect anddrainage result in its replacement by shrub vegetation with Salix glauca, flourishing along streamsides and on south facing slopes, whilst Betula nana dominates slopes with a more northerly aspect.Due to the severe dessication shallow pools may dry out during summer. The climate is low-arcticand continental. The average temperature is 4° C (minimum) and 13° C (maximum) in August, 0° C(minimum) and 7° C (maximum) in September. The examined 14 lakes and pools are situated inlowland between some 50 and 150 m a. s .l. The period of investigation was selected forexperiencing the end of seasonal growth.

2.2. Site characteristics

Water samples were taken at one point in the lakes near the water surface. Habitat conditionswere assessed by measuring the conductivity (LF 90, WTW), pH (digi 88, WTW) and watertransparency (modified Secchi disc). Ground sight is given instead of Secchi depth in some shallowpools. Water temperature was measured regularly during the field studies in one deep lake (site 1)and one shallow pond (site 6) for comparing the particular temperature courses. Hazen colournumber was determined by field method (Merck) in lake 1 and pool 6.

2.3. Species diversity and plant profiles

The submerged plants were recorded and living material for laboratory studies on plant growthand fertility was gathered with access facilitated by the use of snorkelling equipment. As the lakesin their entirety could not be surveyed, the species list does not always correspond to the speciesinventory of the sites studied. Bryophytes, though present in most sites have not been taken intoaccount. The species were grouped according to the ecomorphological system of life-forms, whichhas been established for aquatic macrophytes (Mäkirinta 1978a). The plants observed are classifiedas a helophyte, isoëtid, elodëid or charid species. Helophytes (He) are adapted predominantly toterrestrial life, e.g. they perform a high shoot/ root mass ratio; they inhabit the most shallow water.Isoetids (Is) are characterized by the typical small thick and stiff leaves and by their high root/ shootmass ratio. Elodëids (El) are well adapted to aquatic life, with long shoots and submersed leaves ofsimple anatomy. Charids (Ch) are thallophytes often inhabiting rather deep water. Further growthforms, as Nymphaeids and Lemnids are not found in lakes of arctic Greenland (Fredskild 1992).Helophyte species sometimes exhibit the elodëid life-form, growing completely submerged.Mäkirinta prefers life-forms to growth-forms in his concept, since life-forms account formorphplogical characters plus some ecomorphological adaptations to particular site conditions.

2

The profiles were established employing depth meter und tape measure. In the studies of plantsociology the concept developed by Mäkirinta (1978 b) was used.

2.4. Module characters of Potamogeton species

The shoot morphology of three Potamogeton species was characterized by measuring the lengthof internodes, and the leaf morphology by establishing the length and width of leaves. Leaf lengthwas measured from the point of leaf intersection with the shoot to the leaf apex, leaf width wasmeasured at the widest point along the length of the leaf. Leaf surface area was establishedaccording to the method of Steubing and Fangmeier (1992). Sexual reproduction includes thedevelopment of spike stem and spike; length and width of spike stems and spikes plus the numberof fruit per spike were measured. Fully developed and rudimentary fruit at the same spike werecounted separatedly. Further surveys were carried out on the development of turions and winterbuds. Histograms were established; SPSS and Excel were used for statistics.

3. Results

3.1. Water conditions and species diversity

The water characteristics of the study lakes are listed in Table 1. The sites distinctly vary inseveral aspects: size, conductivity (25° C), Secchi depth, and water colour. Most of the sites aresmaller than 1 ha, the remaining lakes are between 2 and 750 ha. Water is slightly acidic in site 5,and highly alkaline in the sites 9 -14. It is approximately neutral in the remaining lakes 1 – 4 and 6 –8. The conductivity ranges from rather electrolyte-poor (up to 179 µS cm-1 ) in half of the studylakes through moderately rich (up to 633 µS cm-1) in four sites to electrolyte-rich (up to 3920 µScm-1) in the lakes 12 – 14. Secchi depth and water colour usually are correlated: water transparencyis high in clear water (lakes 1 and 9), and lowest in brown water (site 6). Twelve lakes/pools arenatural (e.g. site 11, Store Salt Sø, Fig.1) and the further two are man-made (e.g. quarry lake, site 9,Fig.2).

The following plant species were observed in this study. The taxonomy follows Böcher et al.(1978). According to Fredskild (1992) the species belong to three distribution types: Circum-Greenlandic (1), low-arctic Greenland (2), plus South and/ or West Greenland (3).

(1) Hippuris vulgaris L.Ranunculus confervoides Fr.Ranunculus hyperboreus Rottb.

(2) Eleocharis acicularis (L.) R. et S.Menyanthes trifoliata L.Ranunculus reptans L.Sparganium hyperboreum Laest.Subularia aquatica L.Potamogeton filiformis Pers.

(3) Potamogeton praelongus WulfenMyriophyllum spicatum L. ssp. exalbescens (Fern.) Hult.Potamogeton alpinus Balb. ssp. tenuifolius (Raf.) HultPotamogeton gramineus L.Potamogeton pusillus L. ssp. groenlandicus (Hagstr.) Böch.

3

Charophytes, rare in Greenland to-day, occur in the continental low-arctic interior (Fredskild1992).Chara fragilis Desv.Chara delicatula Ag.Nitella flexilis (L.) Ag. em. R.D.W.Tolypella sp.

The plants observed in the particular lakes are listed in Table 2, arranged according to their life-forms (Mäkirinta 1978a). Many plant species (eight from eighteen) exhibit the elodëid life-form.The other species are distributed to the same extent to the three remaining life-forms.

The species distinctly vary in the number of sites they inhabit: Potamogeton filiformis occurringin nearly all sites and Subularia aquatica in only one lake. P. filiformis experiences the total rangeof ion content, whereas S. aquatica inhabits electrolyte-poor lakes exclusively (Fig. 3). In spite ofthe limited number of the study lakes, the conductivity ranges preferred by the particular species arereasonably consistent with the data given by Fredskild (1992). Furthermore the species vary in theirnutrient demands and conductivity preferences (Fig. 3). Following Fredskild (1992), oneoligotrophic, five oligotrophic-mesotrophic, six mesotrophic and four indifferent species plus twospecies preferring high conductivity are distinguished.

3.2. Site descriptions, depth profiles and plant communities

The sites substantially vary in bottom slope and light availability limiting the area of settlement;furthermore, nutrient and ion content of lake water decide the number of plant species (Table 3).

Water plant symbols are demonstrated in Fig. 4 and applied in the depth profiles (Fig. 5a- j). Site1, Tasersuatsiaq (Lake Ferguson) is approx. 4 km away from Kangerlussuaq Airport (Fig. 5a). Allhelophyte species observed grow together with three isoëtid species in shallow water. Following thedepth gradient, six elodëid species occur with some charid species. Deepest water is inhabited byPotamogeton praelongus and charid species.

The sites 2 (Fig. 5b) and 3 (Fig. 5c) are approx. 30 km apart, near the foot of Sugar Loaf. Pool 2supports each two helophyte and isoëtid species plus some eloëid species in shallow water andPotamogeton praelongus in deepest water. In pool 3 two helophyte and four eloëid species occur inshallow water; deeper than 1.50 m Chara delicatula covers the lake bottom.

The shallow pond 4 (without sketch) is situated on the way to Qaarsorsuaq (Black Ridge) on aplateau, 150 m a.s.l. Three helophytes plus P. filiformis and (more frequently) P. gramineus makeup dense stands, both showing spikes.

Site 5 (Fig. 5d) is a slightly dystrophic shallow pool 750 m (northwest direction) away from lake1. Sparganium hyperboreum exhibits the elodëid life-form and is dotted about here and there,accompanied by Potamogeton filiformis and P. gramineus, both with spikes.

Pool 6 (Fig. 5e), at half way to lake 1, supports vegetation down to only 50 cm, due to poorestlight availability from all sites studied, consisting of helophyte and elodëid species.

The ponds 7 (Fig. 5f) and 8 (Fig. 5g) are situated on the way to Sugar Loaf, approx. 400 m apart.Vegetation of site 7 is made up by helophyte and elodëid species. Potamogeton alpinus occurs inboth sites. In very shallow water of pool 8 the species develops floating leaves exclusively. Themain vegetation belt consists of helophyte, isoëtid and elodëid species. Both sites 7 and 8 supportMyriophyllum spicatum in deepest water.

Lake 9 (Fig. 5h) is the only site with charid life-form dominating the vegetation, correspondingwith the steep bottom slope. The lake is 400 m apart from site 8.

4

In sites 10 (Fig. 5i) and 11 (without sketch) Potamogeton filiformis is prevailing withRanunculus confervoides or R. hyperboreus in shallow water. The lakes are situated on the way toSugar Loaf, one 600 m away from the other.

In both sites 12 and 13 (Fig. 5j) Potamogeton filiformis grows near the water surface, followedby charid vegetation with increasing depth. The lakes are nearby, approx. 10 m between them, onthe way to Umiarsualivik (harbour). P. filiformis plants experience optimal growth conditions inwater with high ion content; a dense seed bank is recognized at the shores (Fig. 6).

Site 14 (without sketch) harbours monospecific stands of Potamogeton filiformis exhibitingluxurious growth.

Plant communities making up vegetation belts are best recognized in lake 1 due to an even slopeand transparent water. They are described in this study by means of synusiae and theircombinations. Synusiae consisting of plants which exhibit the same (or similar) life-forms, areconsidered as ecologically uniform plant societies (Mäkirinta 1978b). They are denoted as “He”,“Is”, “El” or “Ch”, a combination of the first two as “He-Is”.

The following six synusiae/ combinations were established in this investigation:He-Is in lake 1,He-Is-El in sites 2 and 3,He-El in the pools 3, 4, 5, 6, 7,El-Ch in lake 1,El in the sites 1, 2, 10, 11, 12, 13, 14 ,Ch in the lakes 3, 9, 12, 13.The most frequent synusia is El, reflecting the high number of elodëids within the lakes.

3.3. Module parameters of Potamogeton plants

Potamogeton plants develop two kinds of modules, beginning with a basic module. It consists ofa leaf with an axillary bud and a shoot internode. Numerous modules are accumulated, until anotherkind of module appears which is specialized on sexual reproduction. The vertical growth is finishedand a stem bearing a spike is developed. Only one such module per shoot is usually developed (Fig.7). Modular growth may give rise to extreme shoot variation.

The module specialized on growth is characterized by the internode length, leaf width, leaflength and leaf surface area. The data that were established on three Potamogeton species on each25 shoots from site 1, are presented in Table 4. The species distinctly vary in mean leaf parameters,but the mean internode length is similar.

Also for these species the internode length was determined in further sites 5, 6 and in deep waterof lake 1. Size classes for this parameter were defined and six histograms were established (Fig.8–10). The histograms 8a, 9a, 10a are based on data obtained in lake 1 (more shallow water, Table4), and the histograms 8b, 9b, 10b on data received in sites 5, 6 and lake 1 (deep water). Fourhistograms show a peak in the 30-49 mm length class (P. gramineus, 8a, P. alpinus, 9b) or in the50-69 mm length class (P. alpinus, 9a, P. praelongus, 10a). No peak is recognized in the histograms8b and 10b, but with 5-6 similar size classes.

The module specialized on reproduction is characterized by length and width of the spike stem,length of the spike and the number of fruit per spike. Length of spike stem proved to be correlatedwith spike length for Potamogeton alpinus (Fig. 11). Furthermore, width of spike stem is related tolength of spike stem and length of spike. On P. praelongus a regression was established betweenspike length and number of fruit per spike (Fig. 12). All four regressions are compiled in Fig. 13.Hence, the wider and longer the spike stem is, the longer the spike and the more numerous are thefruit.

5

Not all fruit mature, a certain number remains rudimentary until autumn. Table 5 shows resultsof fruit counting on spikes of Potamogeton species in different sites. The share of rudimentaryseeds of P. filiformis is lower in the sites 12 and 13 than in lake 1. Only half of the fruit of P.gramineus mature in site 4. On spikes of P. alpinus (in the sites 6 and 8) and of P. praelongus (insites 2 and 3) all fruit mature. However, on P. alpinus plants developing more than one spike pershoot, (as in very shallow water of site 8), the second and third spikes remained rudimentary. P.praelongus plants produced numerous spikes per shoot in deep water of lake 1, setting of fruit wasscarce until decay of shoots in autumn.

3.4. Observations on survival and reproduction

With the exception of Potamogeton pusillus and Eleocharis acicularis, flowers / fruit wereobserved on all plant species during the time of investigation. Antheridia and archegonia werepresent in all charid species. The flowers of Subularia aquatica (Fig. 15) did not open below thewater surface, as was reported for flowers of Ranunculus confervoides (Böcher 1954). P. pusillusplants develop unusual numerous turions in the leaf axils, appearing dominant in the phenotype. Inthe plant depicted (Fig. 16) the turion, developed in autumn last year, is recognized, that gave rise tothis year shoot growth,and a new turion in its upper part. Several Potamogeton species (P.filiformis, broad-leaved species) overwinter with rhizome buds (Fig. 16). Starch accumulation inautumn is useful for new shoot growth in spring, after the period of dormancy. Myriophyllumspicatum plants exhibit both inflorescence and many turions (Fig. 17). It is supposed that severalspecies overwinter in a green state.

3.5. The end of seasonal growth in the study lakes

The end of the growing season was in late August, in low-arctic, continental Greenland. Fig. 18shows a population of Potamogeton alpinus, beginning to decay. Compared with the very low airtemperature during long winter time, water temperature is even, between 2 and 4° C under the ice.Furthermore, during summer, water temperature does not follow the peaks of the air temperature.During the investigation period water temperature fell from 12.6° to 8.8° C in the deep lake 1, withice covering the shallow bays. In shallow pond 6 the drop in temperature was essential, with 4° Cmeasured in the middle of September. Three temperature curves are presented in Fig. 19, two ofthem representing the values established in the sites 1 and 6. The third gives the mean airtemperatures that were calculated from the daily minimum and maximum values at KangerlussuaqAirport. Usually seasonal growth begins in lakes when water temperature is at least 10° C, so plantgrowth is assumed for approx. 3 months around Kangerlussuaq, from June to August. The aspect ofunder water vegetation corresponded to late summer in the beginning of the investigation and to lateautumn in the end.

4. Discussion

4.1. Species diversity and environment

Except for two species, all the other are reported for Kangerlussuaq surroundings. Subulariaaquatica was observed south of 64.5° and north of 68° n. L (Fredskild 1992, 1996). This newfinding is in between them, at 67° n. l. For Potamogeton praelongus, the second species, a singleisolated finding from central East Greenland was first mentioned by Laegaard (1960); in spite ofintensive floristic work in this Greenland region during the eighties , the species had not been foundagain (Fredskild et al. 1982). Bennicke & Anderson (1998) reported P. praelongus occurring in alake approx. 20 km east of Kangerlussuaq Airport and approx. 7 km west of the marging of theInland Ice. The three new findings of the present study are situated nearer to Kangerlussuaq Airport.

In contrast to the terrestrial vegetation, which is poor in species, Böcher (1954) stresses the realvegetation of hydrophytes around Kangerlussuaq, due to the particular climate conditions. In the

6

present study it is assumed that the high number of lakes and ponds in this area and their variationin site characteristics are essential reasons. Water fowl enable plant dispersal from one lake toanother, where the plant species may settle to if the site conditions consist with the species´demands. Chara fragilis typically makes up dense stands in the man-made site 9, representing apioneer vegetation, typical for man-made lakes (Krause 1981); according to Fredskild (1992) this isthe most frequent among the charid species. In shallow water one single Myriophyllum spicatumplant has settled to this site, according to an optimal ion content, further dispersal of the species inthis lake appears likely.

Hansen (1967) stressed that from a limnological point of view the deeper Greenland lakesdisplay the greatest similarity with the sites on Moskenes island in the Lofoten group, northernNorway. In Table 6 the species inventory of site 1 (= GR1), the deepest lake in the present study, iscompared with the species lists of some lakes in Norway, South Greenland and Iceland, resultingfrom earlier studies (Vöge 1988, 1997a). Site N1 (lake Sottjun) is situated in the south boreal zone,the sites N2 (lake Matthisvatnet) and N3 (lake Jansvatnet) are situated in the north boreal zone,from which N3 is the most northern lake (70.5° n. l.) with some oceanic influence. Plantsexperience a subarctic climate in the lakes GR0, IS1 and IS2. The ion content of all the lakes israther low and does not exceed 159 S cm, water is circumneutral with a pH between 6.8 and 7.5.Sites N1 and GR1 are the richest in species.

Some trends are recognized when comparing the species lists (Table 6), from south borealthrough north boreal/ subarctic to low-arctic conditions: 1.) Nymphaëid species (though possessingfloating leaves, they are adapted preferably to terrestrial life) occur only in the southernmost lakeN1. 2) There is some evidence of species´ replacement with changing climate conditions within theisoëtid species: Lobelia dortmanna and Littorella uniflora retire first, followed by Isoëtes lacustrisand then I. echinospora, whereas Subularia aquatica and Eleocharis acicularis tolerate a coldclimate. 3.) Regarding the remaining life-forms, similarities are displayed: species´ diversity is lowfor the helophyte and charid life-forms with only four species each. The elodëid life-form isrepresented by eight species. Myriophyllum alterniflorum is very rare and Ranunculus peltatus wasnot found in the Greenland lakes, whereas Potamogeton filiformis was observed only in these lakes.This species is known to be a salt tolerant fresh water species, dominating in saline lakes. P. alpinusand P. gramineus are most frequent pond weeds within the selected lakes.

4.2. Groupings of the study lakes

Accounting for water characteristics, plant species and their life-forms, the following sitegroupings are proposed as presented in Table 7:1 ) Sites with approximately neutral water with low conductivity, (sites 1, 2, 3, 4, 5).1a) Clear water lakes supporting isoëtids, Potamogeton gramineus, P. praelongus and Nitella; (sites

1, 2, 3).1b) sites with yellowish water, inhabited by P. gramineus; (sites 4, 5).

2) Lakes with low conductivity and alkaline water, characterized by the elodëids P. alpinus andMyriophyllum spicatum; (sites 6, 7, 8).

3 ) Clear water sites with medium ion content, dominated by a pioneer charid vegetation; (site 9).4 ) Lakes with highly alkaline water; (sites 10, 11, 12, 13, 14).4a) Clear water sites with medium ion content, characterized by P. filiformis, Ranunculus

confervoides or R. hyperboreus; (sites 10, 11).4b) Brownish water lakes with high ion content, alkalinity and pH, inhabited by P. filiformis and

Chara fragilis; (sites 12, 13, 14).Böcher (1954) reported of similar groupings, accounting for 16 lakes/ pools in southern West

Greenland, distinguishing a Potamogeton alpinus-Myriophyllum spicatum-type A and a

7

Potamogeton filiformis-type B. Both types consist with the groupings 2 and 4 of the present study.The additional groupings 1 and 3 are based on the findings of Subularia aquatica and Potamogetonpraelongus (group 1) and on the observed deep water charid vegetation (group 3). This group isrepresented by only one lake. This site (9) is man-made with particular water conditions; such lakesprobably did not exist 50 years ago. It is supposed that man-made sites, e. g. quarry lakes, will bemore frequent in future.

The plant species surveyed essentially vary in their demands on nutrient/ ion contentcorresponding to the variation of site characteristics. Accounting for the representation ofoligotrophic, oligo-mesotrophic, mesotrophic species, and species preferring high conductivity, plusindifferent species in the particular sites (Fig. 3, Table 8), another site grouping appears reasonable,distinguishing site type I, (consistent with former group 1a), site type II, (embracing the formergroups 1b and 2), site type III, (containing the former groups 3 and 4a), plus site type IV, (consistentwith former group 4b).

Each site type is uniform in light availability, as indicated by water colour and Secchi depth.Mean conductivity was calculated for each site type. Regarding the species´ demands, the types arecharacterized in the following way:Site type I: oligotrophic-mesotrophic, high light availability, 114 µS cm-1, sites 1, 2, 3.Site type II: (oligotrophic)-mesotrophic, reduced light availability, 139 µS cm-1 , sites 4, 5, 6, 7, 8.Site type III: mesotrophic, high light availability, 620 µS cm-1 , sites 9, 10, 11.Site type IV: saline, reduced light availability, 3500 µS cm-1 , sites 12, 13, 14.

Potamogeton species experience different light availability in site types I and II, P. filiformis,growing in site types II and IV, experience different ion contents. These types are the mostinformatives with regard to the environment influencing growth parameters.

4.3. Zonation of plant communities

Usually, different water plant communities are recognized to follow the bottom downward slope.The zonation, characteristic for a particular lake, is described by a sequence of vegetation belts.Plant communities are denoted by synusiae and combinations, in the present study. “HeIsVeg”means a vegetation belt, representing a combination of helophyte and isoëtid synusia. The followingsequences of plant communities, so-called zonation types (ZT), were established in the study sites:

(ZT 1) HeIsVeg- ElVeg- ChVeg, in site 1(ZT 2) HeIsElVeg- ElVeg, in site 2(ZT 3) HeElVeg- ChVeg, in site 3(ZT 4) HeElVeg, in sites 4, 5, 6. 7(ZT 5) IsElVeg- ElVeg, in sites 2, 8(ZT 6) ChVeg, in site 9(ZT 7) ElVeg, in sites 10, 11, 14(ZT 8) ElVeg- ChVeg, in sites 12, 13The most frequent zonation type is (ZT 4) with one plant community, the most complete

zonation type is (ZT 1), in site type I/ lake 1), with three plant communities, comprising all life-forms examined. This is possible only if all habitat conditions, required by the the life-forms arefulfilled: oligo-mesotrophic conditions, high water transparency, and appropriate site morphology,that is a deep lake with an even slope. Site 1 is the only one offering all these conditions. In the sitetype II/ ponds 4, 5, 6, 7 supporting one plant community, low light availability causes a narrowvegetation belt. Zonation types (ZT 7) and (ZT 8) characterize lakes with high ion content, site typesIII and IV.

8

4.4 .Leaf and shoot morphology of Potamogeton species

Shoots elongate due to repetitive growth, the length of modules agreeing with the internodelength. In type I/ site 1 leaf area and mean internode length increase from Potamogeton gramineusthrough P. alpinus to P. praelongus, growing in shallow water (Tab. 4), corresponding with theshoot length of the species. Usually, the internode length is rather constant for a particular species.As was expected, this pattern is recognized in the size-class diagrams in Fig. 8a (P. gramineus), Fig.9a (P. alpinus) and Fig. 10a. The diagram in Fig. 10a is compared with that in Fig. 20. Bothrepresent P. praelongus and they are much alike. Since data of lake Großensee in C Europe (Vöge,unpubl.) were employed for Fig. 20, the comparison supports to the interpretation of the internodelength to be largely independent of climate conditions.

The diagrams in Fig. 8b (Potamogeton gramineus), Fig. 9b (P. alpinus) and Fig. 10b (P.praelongus) exhibit more variation and no clear peak is recognized in the internode length of P.gramineus or P. praelongus. The tend towards to more variable and longer internodes is explainedby particular site conditions. P. gramineus and P. alpinus inhabiting site type II/ ponds 5, 6experience low light conditions, P. praelongus suffers from deep settlement in site type I/ lake 1.Internode elongation due to a deficit in light makes sense, since shoot elongation results inaccelerating the shoot growth and approximating the shoot apex to the water surface with betterlight conditions. The essential internode elongation in P. praelongus (Fig. 10a, compared with Fig.10b) displays a within lake variation in clear water lake 1. Inflorescence usually is developed, whenthe shoot apex is near the water surface. Ressource allocation assumably is insufficient forproducing a shoot of four meter length plus setting of fruit. There is some evidence indicating acompromise: in spite of internode elongation the shoot apex remains far from the water surface ,nevertheless inflorescence is developed but remain rudimentary until the end of seasonal growth.

Variation in the internode length and internode elongation are less distinct in Potamogetonalpinus than in the other broad-leaved species. One explanation may be found in better tolerating oflow light conditions in P. alpinus, this view being supported by the preference of type II habitats inthe present study.

The product of leaf length and leaf width proved to be correlated with the leaf surface area, validfor seven Potamogeton species, growing in different climate conditions (Vöge, in press). Theregression is depicted in Fig. 21. Data from the present study on three Potamogeton species (Table4) are expressed by dots. The expression of this relationship is consistent between the earlier resultsand the present study. It should be noted that the leaf surface area of P. alpinus is the same in sitetype I/ lake 1 and site type II/ pond 6, independent of light availability.

The leaf surface area is larger on Potamogeton gramineus and P. praelongus in Greenland thanin a temperate climate. Furthermore, the leaf length/ leaf width ratio is higher in all threePotamogeton species. Data established in lakes of C Europe (Vöge, in press) and from the presentstudy are listed in Table 9. It appears that the higher values are due to low-arctic climate.

The influences of light and water temperature on the growth of submersed macrophytes aredifficult to separate from one another during field studies. For a discussion of the variation studiedbetween the lakes around Kangerlussuaq water temperature influences are not to be considered.However, compared with data established in a temperate climate, effects of cold water may beevaluated. Barko & Smart (1981) emphasize that both light and water temperature may be of equalimportance with regard to macrophyte growth. According to laboratory studies, the leaf surface areaof Potamogeton nodosus Poiret and leaf length/ leaf width ratio are reported to increase withdecreasing water temperature (Barko & Smart, 1981), thus supporting the results from the threePotamogeton species studied in Greenland (Table 9). The leaf-form was found unaffected by light(Barko et al. 1982). This result is consistent with P. alpinus leaves exhibiting the same length andwidth in site type I and II. Variations in shoot length effected by irradiance reflect internodeelongation which can be influenced by temperature as well; Berry & Bjorkman (1980) caution the

9

interactive relationship between light and temperature. Furthermore, the depth of settlement mayinfluence the internode length, as is recognized in the within-lake variation of P. praelongus in site1 (Fig. 10).

4.5. Spike and fruit development of Potamogeton species

Phillip et al. (1990) emphasize sexual reproduction to be a common physiological reactiontoward extreme environment. On the other hand sexual reproduction is a rare event even though ahigh number of seeds may be produced, up to 135 000 per square meter, and vegetativereproduction is predominant in Potamogeton (Vöge 1997b, Wiegleb & Brux 1991). According toCallaghan & Collins (1981) vegetative reproduction is preferred to sexual reproduction in arcticareas, due to the limited ressource allocation and difficult establishment of seeds and shoots.

With regard to the number of seeds per shoot (Table 5) successful sexual reproduction appearsunlikely for four Potamogeton species. Only P. filiformis, exhibiting a remarkable shoot density andhigher seeds production in lakes with high ion content, effects a vigorous seed-bank. With theexception of P. gramineus (Fig. 14) one spike per shoot is developed, however, two spikes arefrequently observed in P. filiformis growing in lakes with high conductivity (Fredskild 1992). Sinceinflorescence is developed near the water surface, light conditions as indicated by Secchi depth andwater colour are presumed with low influence. The more numerous fruit per P. alpinus shoot inextremely shallow water (site 8) compared with some deeper water (site 6) is supposed to be due tovarying ressource partitioning. Though sexual reproduction is unlikely, the importance of evenmodest seed-banks is stressed as they may enable resettlement after disturbance (Haag 1983, Van deWeyer 1988).

Spike stems and the (fruit-bearing) spikes characterize the reproduction-specialized modules.The highly significant regression between length of spike stem and spike length of Potamogetonalpinus (Fig. 11) established in sites 6 and 7, is not valid for such plants growing in the particularconditions of site 8. The relationship between the spike length and the number of mature fruit perspike, established on P. praelongus in sites 2 and 3 (Fig. 12), provides explanation for therudimentary spikes observed in deep water of lake 1: shorter than 2.5 cm, no fruit mature on suchspikes. In contrast to the spike length, the spike stems are as long as in sites 2, 3 and consistent withdata from lakes in C Europe (Tab.10), according to Casper & Krausch (1980). This contrast appearsdue to limited ressource availability. Spike stems and spikes of P. gramineus are essentially shorterin Greenland site 4 compared with data from C Europe (Table 10). It appears that this Potamogetonspecies suffers most from the low-arctic climate. This trend is less pronounced in P. alpinus.

Summarizing, the mentioned authors support the observations of this study. Sexual reproductionseems emphasized considering the conspicuous inflorescence development (e.g. Fig. 22), but thenumber of mature fruit is low. So vegetative reproduction by means of specialized vegetativepropagules or fragmentation of clonal growing plants appear to prevail.

4.6. Diversity in shoot complex development

The life-cycle of Potamogeton species usually begins in late March, and is finished in October ina temperate climate (Vöge 1997, Wiegleb & Todeskino 1985). After a period of dormancy of thereproductive unit horizontal and vertical shoots are growing continually, sexual reproduction endsin August/ September, fragmentation of the shoot complex and vegetative reproduction indicate theend of seasonal growth, when shoot decomposition begins. The result of a growing season of sixmonths in displayed in Fig. 23: a shoot complex of P. perfoliatus in lake Hohendeicher See in CEurope. From a horizontal shoot, two meters long, nineteen vertical shoots arise, with a total lengthof more than ten meters. The branching of the horizontal shoot is recognized, giving rise to furthervertical shoots. These shoots vary in their length according to different age (Vöge 1997b). Incontrast, shoot complexes are somewhat rudimentary in low-arctic climate. The shoots within apopulation are of approximately the same length, indicating that continued growth of shoots does

10

not belong to the set of options established in Potamogeton species growing in a temperate climate.Further options, that is growth patterns which enable survival of a population (Chapleau et al 1988,Van de Weyer 1997) are: clonal growth, including asexual reproduction, morphological plasticityand sexual reproduction.

Particular development of shoot complex was observed in sites with very special growthconditions. Fig. 24 shows a Potamogeton alpinus shoot complex from site 8 exhibiting the typicalfeature as known from a temperate climate, but miniaturized due to low water level. Maximumshoot length is only ten centimeters, reducing the energy that must be expended on vegetativegrowth. Ressource partitioning favours sexual reproduction which is evident in the three spikesdeveloped on one shoot, however, only the fruit of one spike matured. P. alpinus in site type II/pond 6 displays a divergent shoot complex, and is presumed an adaptation to low light availability(Fig. 25). Shortcoming light is experienced by horizontal shoots near the bottom, whereas thesehorizontal shoots arising from the upper vertical shoot are advantaged. Limited resources appear toexplain the absence of inflorescence. P. praelongus exhibits an unusual growth-form in deep waterof lake 1 (Fig. 26). One vertical shoot developed numerous side-shoots with one inflorescence each,but all of them were rudimentary.

Though some positive correlations between plant parameters were established, compromisesappear frequent in Greenland climate conditions. This result supports the opinion of Law (1979),accordingly positive correlations reflect optimal growth conditions, whereas compromisses areexpected in suboptimal environment.

5. Conclusions

Human influence on lakes and pools around Kangerlussuaq is low. For the last decades, man-made lakes were added to the high number of natural sites in this region. Such young lakes/ poolsmay support some pioneer vegetation in an early stage after sediment stabilization, until furtherspecies settle if site characteristics are appropriate.

Water plants may experience stress and disturbance. Stress, following Grime (1979) affects theincrease of biomass, and results here from low water temperatures during the short growing seasonand low light availability in dystrophic sites. Some further stress is experienced by Potamogetonplants growing in deep water. Disturbance reduces (partly or totally) the biomass (Grime 1979). Itmay be caused by the dry climate in this particular region. Due to lowering of water level thesubmersed leaves of Potamogeton alpinus decayed, and a few floating leaves developed in site 8.

Vegetative reproduction by means of specialized vegetative propagules or fragmentation ofclonal growing plants appears to prevail. However, some modest seed banks may enableresettlement of species after disturbance.

6. Acknowledgements

The author is greatly indebted to Danish Polar Center for the allowance to stay and work atKangerlussuaq International Science Support; to Christian Bay, Botanical Museum, University ofCopenhagen for valuable information; to Fleming Skou, Danish Meteorological Institute,Copenhagen, for climate data; to Antje Eggers, Hamburg, who has corrected the English text; and tomy husband Harald Vöge for continued assistance.

7. References

Barko, J. W. & Smart, R. M., 1981: Comparitive influences of light and temperature on growth andmetabolism of selected submersed freshwater macrophytes. - Ecol. Monogr. 51: 219 - 235.

Barko, J. W. , Hardin, D. G. & Matthews, M. S., 1982: Growth and morphology of sumersedfreshwater macrophytes in relation to light and temperature. - Can J. Bot. 60: 877 - 887.

11

Bay, C., 1992: A phytogeographical study of the vascular plants of Northern Greenland- north of74° northern latitude. - Meddr Grønland. Biosci. 36.

Bennicke, O. & Anderson, J.N., 1998: Potamogeton praelongus in West Greenland. - Nord. J.Bot.18: 499 - 501.

Berry, J. B. & Bjorkman, O., 1980: Photosynthetic response and adaptation to temperature in higherplants. - Annu. Rev. Plant Physiol. 31: 491 - 543.

Birks, J. D. S. & Penford, N., 1990: Observations on the ecology of arctic foxes Alopex lagopus inEqalummiut Nunaat, West Greenland. - Meddr Grønland Biosci. 32.

Böcher, T. W., 1949: Climate, soil and lakes in continental West Greenland in relation to the plantlife. - Meddr. Grønland 147.

Böcher, T. W., 1954: Oceanic continental vehetatuional complexes in southwest Greenland. -Meddr. Grønland 148, Nr. 1.

Böcher, T. W., 1963: Physiography of middle West Greenland. - Meddr Grønland. 148, Nr. 3.

Böcher, T. W., Fredskild , B., Holmen, K. & Jakobsen, K., 1978: Grønlands Flora. - Copenhagen

Callaghan, T. V. & Collins, N. J., 1981: Life cycle, population dynamics and the growth of tundraplants. - In: Bliss, L. C. Heal, O. W., Moore, J.J. (eds.): Tundra Ecosystems: a comparativeanalysis. IBP 25: 257- 284, Cambridge.

Casper, S. j. & Krausch, H. -D., 1981: Süßwasserflora von Mitteleuropa. - Bd. 24: Jena.

Chapleau, F. Johanson, P.H. & Williamson, M., 1988: The distinction between pattern and processin evolutionary biology: the use and abuse of the term "strategy". - Oikos 53; 136 - 138.

Fredskild, B., 1992: The green limnophytes- their present distribution and Holocene history. - ActaBot. Fennica 144: 93 - 113.

Fredskild, B., 1996: A phytogeographical study of the vascular plants of W Greenland (62°20´ -74°00 N)´ - Meddr Greenlamd, Biosci. 45

Fredskild, B., Bay, C. & Holt, S., 1982: Botaniske undersøgelser på Jameson Land - BotaniskMuseum, København

Grime, J. P., 1979: Plant strategies and vegetation processes. - Wiley, Chichester, pp. 7-119.

Haag, W., 1983: Emergence of seedlings of aquatic macrophytes from lake seedlings. - Can. J. Bot.:61: 148 - 156.

Hansen, K., 1967: The general limnology of arctic lakes as illustrated by examples from Greenland.- Meddr. Grønland 178, Nr. 3.

Krause, W., 1981: Characeen als Bioindikatoren für den Gewässerzustand. - Limnologica. 13: 399-418

Law, R., 1979: Ecological determinants in the evolution of life histories. - In: R. M. Anderson, B.D. Turner & L. R. Taylor (eds), Population Dynamics, Oxford, 315 - 345.

Lægaard, S., 1960: Two species of Potamogeton new to Greenland. - Bot. Tidskr. 56: 247 – 251.

Mäkirinta, U., 1978a: Ein neues ökomorphologisches Lebensformensystem der aquatischenMakrophyten. - Phytocoenologia 4: 446-470.

Mäkirinta, U., 1978b: Die pflanzensoziologische Gliederung der Wasservegetation im See Kukkia,Südfinnland. - Acta Univ. Ouluensis, Ser. A, 75(5): 157 S., Oulu.

12

Philipp, M., Böcher, J., Mattsson, O. & Woodell, S. R. J., 1990: A quantitive approach to the sexualreproductive biology and population structure in some arctic flowering plants: Dryasintegrifolia, Silene acaulis and Ranunculus nivalis. - Meddr. Grønland, Biosci. 34.

Steubing, L. & Fangmeier, 1992: Pflanzenökologisches Praktikum. - Stuttgart.

Vöge, M., 1988: Tauchuntersuchungen an der submersen Vegetation in skandinavischen Seen unterbesonderer Berücksichtigung der Isoetiden-Vegetation. - Limnologica 19/2: 89-107.

Vöge, M., 1997a: Plant size and fertility of Isoëtes lacustris L. in 20 lakes of Scandinavia: a fieldstudy. - Arch. Hydrobiol. 139: 171-185.

Vöge, M., 1997b: Vegetationskundliche und populationsbiologische Untersuchungen imHohendeicher See in Hamburg. - Tuexenia 17: 109 – 123.

Vöge, M., 2001: Beschreibung von Wachstum und Entwicklung und Isoëtes mittels Korrelationen;Ein Vergleich. - Tuexenia (in press).

Weyer, K. van de, 1988: Ein Wiederfund von Potamogeton coloratus VAHL am Niederrhein. -Natur am Niederrhein N. F. 3: 46 - 48.

Weyer, K. van de, 1997: Untersuchungen zur Biologie und Ökologie von Potamogetonpolygonifolius Pourr. im Niederrheinischen Tiefland - Diss., Berlin. Stuttgart

Wiegleb, G. & Brux, H., 1991: Comparison of life history characters of broad-leaved species of thegenus Potamogeton L. General characterization of morphology and reproductive strategies. -Aqua. Bot. 39: 131 - 146.

Wiegleb, G. & Todeskino, D., 1985: Der biologische Lebenszyklus vpn Potamogeton alpinus unddessen Bedeutung für das Vorkommen der Art. - Verh. Ges. f. Ökologie XIII: 191-198.

13

Table 1: Characteristics of the study sites

Siteno.

Position Size(ha)

pH Conductivity(µS cm-1)

Secchi depth(m)

Water colour

1 N66.98342 W50.69003 Z750 7.5 75 10.0 clear

2 N67.03912 W50.56249 Z 2 7.7 130 1.2* clear

3 N67.03930 W50.56017 Z 10 7.5 137 1.5* clear

4 N67.00875 W50.64190 < 1 7.0 233 1.0* yellow

5 N66.98274 W50.70811 < 1 6.6 61 0.8* yellow

6 N66.99789 W50.67268 < 1 7.0 125 0.6 brown

7 N67.02941 W50.61394 < 1 7.7 179 2.0* slightly yellow

8 N67.02991 W50.60421 < 1 7.9 94 1.0* slightly yellow

9 N67.02989 W50.59450 < 1 8.2 419 >4.0 clear

10 N67.02271 W50.65397 < 1 8.4 607 1.0* slightly yellow

11 N67.02377 W50.66665 < 1 8.6 633 3.0* clear

12 N67.00062 W50.80527 < 1 8.7 3470 3.0* slightly brownish

13 N67.00010 W50.80560 < 1 8.7 3920 3.0* slightly brownish

14 N66.98829 W50.58403 Z 30 9.0 3110 2.0* slightly brownish

*) Bottom sight

14

Table 2: Plant species observed in the study sites

Lifeform

Species Site no.

1 2 3 4 5 6 7 8 9 10 11 12 13 14

He, El Menyanthes trifoliata + + +

Hippuris vulgaris + + + + + + +

Sparganium hyperboreum + + + + + + + +

El Potamogeton alpinus + + + +

Potamogeton filiformis + + + + + + + + + + + +

Potamogeton gramineus + + + + +

Potamogeton praelongus + + +

Potamogeton pusillus + + +

Myriophyllum spicatum + + + +

Ranunculus confervoides + + + + + +

Ranunculus hyperboreus + +

Is Ranunculus reptans + + +

Subularia aquatica +

Eleocharis acicularis + +

Ch Chara fragilis + + +

Chara delicatula +

Nitella flexilis +

Tolypella sp. +

Table 3: Ranges of the site characteristics

Characteristics Range

Size (ha) <1 - 750

pH 6.6 - 9

Conductivity (µS cm -1) 61 - 3920

Secchi depth (m) 0.6 - 10

Water colour Clear - brown

Hazen colour number 5 - 300

No. of plants species per site 1 - 14

Depth limit of vegetation (m) 0.6 - 6

15

Table 4: Characteristics of vegetative growth for three Potamogeton species in lake 1

Species Mean internodelength(cm)

Mean leaflength(cm)

Mean leafwidth(cm)

Mean leafarea(cm²)

Potamogeton gramineus 5.0 6.5 0.8 3.4

Potamogeton alpinus 5.2 11.9 0.9 7.5

Potamogeton praelongus 6.0 15.2 1.8 19.6

Table 5: Fruit production of four Potamogeton species in different sites

Species Site Mean number of seeds per spike

G mature rudimentary

Mean number ofseeds per shootG mature

Potamogeton filiformis 12, 13 4 6 8-16

Potamogeton filiformis 1 2 7 6

Potamogeton gramineus 4 8 8 16

Potamogeton alpinus 8 109 - 109

Potamogeton alpinus 6 35 - 60 - 35 - 60

Potamogeton praelongus 2, 3 55 - 55

16

Table 6: Plant species in lakes of Norway, Greenland and Iceland

Lifeform

Species Lake no.

N1 N3 GR0 IS1 N2 IS2 GR1

He, El Menyanthes trifoliata +

Hippuris vulgaris + + +

Sparganium angustifolium + + +

Sparganium hyperboreum + +

Ny Nymphaea candida +

Potamogeton natans +

El Myriophyllum alterniflorum + + + + +

Ranunculus peltatus +

Potamogeton alpinus + + + + +

Potamogeton filiformis + +

Potamogeton gramineus + + + +

Potamogeton praelongus + +

Potamogeton pusillus + +

Ranunculus confervoides +

Cer, El Utricularia ochroleuca +

Is Juncus bulbosus +

Lobelia dortmanna +

Littorella uniflora +

Isoëtes lacustris + +

Isoëtes echinospora + +

Ranunculus reptans + +

Subularia aquatica + + + +

Eleocharis acicularis +

Ch Chara delicatula +

Chara fragilis +

Nitella flexilis + + + +

Tolypella sp. +

17

Table 7: Site groupings according to site conditions and vegetation

Sitegroup

Site no. Site conditions Vegetation

Water colour pH Ion content Dominant life- forms and species

Clear Yellow-brown

Circum-neutral

alkaline Highlyalkaline

Low Medium High Isoëtids Elodëids Charids

Nitella Chara

1a 1, 2, 3 + + + + P. gramineus, P. praelongus +

b 4, 5 + + + P. gramineus

2 6, 7, 8 + + + P. alpinus, M. spicatum

3 9 + + + +

4a

b

10, 11

12, 13, 14

+

+

+

+

+

+

P. filiformis, Ranunculus sp.

P. filiformis +

Table 8: Number of species with different demands for nutrient / ion content in the sites studied

Species Site no.

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Oligotrophic species 1

Oligotrophic-mesotrophic species 6 5 3 3 2 3 1 3 1

Mesotrophic species 3 1 1 1 1 1 1 1

High conductivity preferring species 1 1 2 1 1 1 2 1 1 1 1 1 1 1

Indifferent species 3 3 1 1 2 2 2 1

Table 9: Leaf area and leaf length / leaf width in a) low- arctic lake 1, b) temperate climate, for threePotamogeton species.

Species Leaf area (cm²) Leaf length / leaf width

a b a b

Potamogeton praelongus 19.6 16.8 8.4 6.4

Potamogeton alpinus 7.5 11.0 13.3 8.2

Potamogeton gramineus 3.4 2.3 8.1 5.2

Table.10: Length of spike stems and spikes in Greenland sites compared with C European (CE) sites

Parameter Potamogetonpraelongus

Potamogetongramineus Potamogeton alpinus

CE* 1** 2, 3 CE* 4 CE* 6 8***

Length of spike (cm) 2 - 4 1.2 3.3 2 - 3 0.8 2 - 4 1.6 2.3

Length of spike stem (cm) 5 - 30 24.5 26.0 2 - 6 1.8 5 - 15 4.3 3.3

*) According to Casper & Krausch (1980)**) Rudimentary spikes in deep water

***) In extremely low water level

Fig. 1: Site 11

19

Fig. 2: Site 9, a quarry lake

20

Fig. 3: Number of findings, conductivity ranges (µS cm-1) and demands on nutrient/ ion content ofthe speciesa: Oligotrophic speciesb: Oligo- mesotrophic speciesc: Mesotrophic speciesd: Species preferring high conductivitye: Indifferent species

21

12: Potamogeton filiformis 61 – 3920 d8: Sparganium hyperboreum 61 - 233 b7: Hippuris vulgaris 75 - 233 e6: Ranunculus confervoides 61 - 633 e5: Potamogeton gramineus 61 - 233 b4: Potamogeton alpinus 75 - 179 c4: Myriophyllum spicatum 94 - 419 d3: Potamogeton praelongus 75 - 137 b3: Potamogeton pusillus 75 - 137 b3: Ranunculus reptans 75 - 130 b3: Chara fragilis 419 – 3920 c3: Menyanthes trifoliata 175 - 233 b2: Eleocharis acicularis 75 - 130 e2: Ranunculus hyperboreus 125 - 607 b1: Chara delicatula 137 c1: Nitella flexilis 75 c1: Tolypella sp. 75 c1: Subularia aquatica 75 a

Fig. 4: Species symbols

22

Potamogeton pusillus

Potamogeton gramineus

Potamogeton praelongus

Potamogeton filiformis

Potamogeton alpinus(floating/submersed)

Chara fragilis

Menyanthes trifoliata

Hippuris vulgaris

Sparganium hyperboreum

Myriophyllum spicatum

Ranunculus reptans

Subularia aquatica

Nittella flexilis

Ranunculus confervoides

Eleocharis acicularis

Tolypella sp.

Chara delicatula

Ranunculu hyperboreus

Fig. 5a: Site 1

23

2m

6m

Fig. 5b: Site 2

Fig. 5c: Site 3

24

1.20m

1.50m

Fig. 5d: Site 5

Fig. 5e: Site 6

25

0.75m

0.6 m

Fig. 5f: Site 7

Fig. 5g: Site 8

26

1m

1m

Fig. 5h: Site 9

Fig. 5i: Site10

27

3m

0.5m

Fig. 5j: Site 12, 13

Fig. 6: Seed bank of Potamogeton filiformis, site 12

28

3m

Fig. 7: Spike of Potamogeton alpinus in site 6

29

Fig. 8: Size class diagrams: internode length for Potamogeton gramineus, site 1 (left), site 5 (right)

Fig. 9: Size class diagrams: internode length for Potamogeton alpinus, site 1 (left), site 6 (right)

30

0

52

36

12

0 0 0 0

10,2

22,2

15,5

20

14,4 15,5

2,20

1

35

60

40 0 0 0

7,1

18,6

44,3

24,3

2,9 2,80 0

-29 -49 -69 -89 -109 -129 -149 -169

-29 -49 -69 -89 -109 -129 -149 -169

Fig. 10: Size class diagrams: internode length for Potamogeton praelongus, site 1, shallow water(left), site 1, deep water (right)

Fig. 11: Relationship between spike length and spike stem length for Potamogeton alpinus, site 6

31

6,3

27,5

37,5

15

8,8

2,5 1,2 1,2 0 0

12,7

20 18,3

23,621,8

3,6

-29 -49 -69 -89 -109 -129 -149 -169

y = 0,3976x + 0,0758

R2 = 0,7339

0

5

10

15

20

25

0 10 20 30 40 50 60

Length of spike stem (mm)

Spik

ele

ngth

(mm

)

Fig. 12: Relationship between spike length and number of fruit per spike for Potamogetonpraelongus, sites 2,3

Correlations between:

1: Length of spike stem and spike length2: Length of spike stem and width of spike stem3: Width of spike stem and spike length4: Spike length and number of seeds per spike

1, 2, 3: Established on Potamogeton alpinus in site 64 : Established on Potamogeton praelongus in sites 2, 3

Fig. 13: Significant regressions between Potamogeton module parameters

32

y = 2,9007x - 39,85

R2 = 0,5424

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25 30 35 40 45

Spike length (mm)

Nu

mb

ero

ffr

uit

sp

ersp

ike

2

1 4

3

Mean width ofspike stem

mean number ofseeds per spike

mean spikelength

Mean lengthof spike stem

P < 0.001P < 0.01

Fig. 14: Spikes of Potamogeton gramineus in site 4 (left) and of Potamogeton filiformis in site 13(right)

33

Fig. 15: Subularia aquatica in site 1

34

Fig. 16:(left) Potamogeton pusillus with last year turion (1) and this year turion (2).(right) Rhizome bud of Potamogeton filiformis

35

ø2

ø1

Fig. 17: Myriophyllum spicatum with inflorescence and turions

36

Fig. 18: Potamogeton alpinus in site 1 in the end of seasonal growth

Fig. 19: Air and water temperature during the study time

37

08/18/2000 08/25/2000 09/01/2000 09/08/2000 09/15/20000

4

8

12

16

Date

Tem

pera

ture

(°C

)

(Site 1)

Air temperature(means)

Water temperature(surface)

(Site 6)

Fig. 20: Size class diagram: internode length for Potamogeton praelongus in temperate climate

Fig. 21: Correlation between leaf width * leaf length and leaf surface area

38

y = 0,6994x + 0,3202R2 = 0,9864

0

10

20

30

40

50

0 10 20 30 40 50 60 70

Leaf width * leaf length (cm²)

Lea

fsur

face

area

(cm

²)

Spalte 45

7,9

28,9

47,4

10,5

5,3

0 0 0

-29 -49 -69 -89 -109 -129 -149 -169

Fig. 22: Potamogeton alpinus shoot with 3 spikes in site 8

39

Fig. 23: Shoot complex of Potamogeton perfoliatus in temperate climate, in August

40

207 cm

203 cm

Fig. 24: Shoot complex of Potamogeton alpinus in very low water level, site 8

Fig. 25: Shoot complex of Potamogeton alpinus with horizontal shoots 1,2,3, in site 6

41

10 cm

3

2

1

Fig. 26: Potamogeton praelongus shoot, with side-shoot-bearing and apical inflorescence, in site 1,4 m deep

42

28cm

43cm

27cm

8cm

38cm

7 mm

12 mm

10 mm

20 mm

11 mm

Spike lengthInternode length