Freshwater ecology:The functioning of freshwater ecosystems

Mara J. ServiaDepartamento de Bioloxa Animal, Bioloxa Vexetal e Ecoloxa

maria.servia@udc.es

WATER TREATMENT FOR?

Types of freshwater habitats

LENTIC HABITATS (lakes, ponds, reservoirs...)

LOTIC HABITATS (rivers, streams)Rivers have riffles (regions of shallow, rapid water) and pools (deep, slow water).

SPECIAL HABITATS

Types of freshwater habitats

Special habitats

Special habitats

HYPERSALINE POOLSHigh salinity due to soluble rock beds.

TEMPORAL POOLSIn rocks, plants

PEAT BOGS (TURBERAS)Highly endemic fauna and flora.

Special habitats

CAVE STREAMSAbsence of light. Organisms are adapted to theseconditions

HYPORHEIC ZONERegion below the level of the stream bottom wherewater fills the spaces between the stones, gravelsand sand.

THERMAL SPRINGSOccur in regions where hot magma is close to the earthsurface.

The functioning of freshwater ecosystems

All ecosystems need a source of energy. Main source is the sun.Organic carbon compounds are formed out of carbon dioxide andother inorganic matter, capturing the energy of sunlight viaphotosynthesis. We call this primary production (autotrophs) because it creates new organic matter from inorganic precursors. The rest of the organisms comsume the organic matter formed by primary producers; they are heterotrophs or consumers. Whenconsumer organisms grow and reproduce, we call this secondaryproduction. Virtually all life on earth derives its energy from thesun, via primary production. Autotrophs and heterotrophs use thatenergy to do metabolic work, and in the process convert energycontained in organic carbon compounds back into inorganic matter(respiration).

Food webs are the feeding relationshipsinto the ecosystem, that is: the fluxes ofmatter and energy.

LENTIC HABITATS

LOTIC HABITATS

THE ORGANISMS. Have a look at http://www.youtube.com/watch?v=jjCfXurWRJw&feature=relmfu

Plankton: Organisms living in the water column, carried by water movements. Normally < 5 mm.

Nekton: Organisms living in the water column, butwith active movements. Ex. fish.

Neuston: Organisms living in the air-waterinterface. They benefit from the water surfacetension.

Benthos: Organisms living in the bottom ofbodies of water (lakes, ponds, rivers, streams).

Macroinvertebrates: Benthic invertebrates(mostly!) visible with the naked eye.

Macrophytes: Macroscopic plants..

The functioning of freshwater ecosystems

Lentic habitats

Lentic habitats

They are temporal habitats. Most tend to collapse with sediments anddissapear. In glacial lakes the rate of settling of the sediment is about1mm/year.

Lakes are inland bodies of freshwater that may have dramatically different temperatures from the surface to the bottom (thermocline). Light generally does not reach bottom at deeper points.

Ponds are much smaller than lakes and usually have the same temperature from top to bottom. Light generally will reach the bottom in all areas of the pond.

Lentic habitats

5 10 15 20 25 30

12345678910

Temperatura (C)

Pro

fund

idad

(m)

Epilimnion

Hipolimnion

MetalimnionTERMOCLINA

Lentic habitats

A thermocline is a thin but distinct layer in a large body of fluid (e.g. an ocean or lake) in which temperature changes more rapidly with depth than it does in the layers above or below

Lentic habitats

Photic zone : is the depth of the water that is exposed to sufficient sunlight for photosynthesis to occur. Primary production is higher than respiration.

Aphotic zone: the depths beyond which less than 1% of sunlight penetrates. Respiration is higher than primary production.

The depth of the photic zone can be affected greatly by seasonal turbidity.

LIGHT% of surface light

0

5

10

15

20

25

30

35

0 25 50 75 100

dept

h (m

)

10%20%

Lentic habitats

Pseudotaxonomic clasificationBACTERIOPLANKTON

PHYTOPLANKTON

ZOOPLANKTON

Lentic habitats

Plants need P and N. In a lentic body of water their excess favours a high primaryproduction. Water becomes green due to the accumulation of phytoplankton.

Phytoplankton seasonal succession occurs in relation to seasonal changes in lightand temperature.

Eutrophication

BiomarcadoresLentic habitats

Eutrophication favours the occurrence ofHABs: harmful algal blooms. Normally diversity is reduced and cyanobacteria dominate. Cyanobacteria produce a variety of toxins.

Caldas de Reis (Pontevedra), 2006

Phytoplankton blooms

The functioning of freshwater ecosystems

Lotic habitats

Lotic habitats

Carpa

Correlation between fish assemblages and physical factors such as river slope, depth, width

Brema

Trout zone Grayling zone Barbel zone Bream zone

TruchaCavilat

Bermejuela

TmaloGobio

Boga

Lamprea de ro Alburno

Barbo Tenca

EscardinoPerca

Anguila

Lucio

Salmonid region Cyprinid region

Carpa

Brema

The longitudinal distribution of fish (Huet, 1949)

THE LONGITUDINAL ZONATION OF RIVERS

BiomarcadoresLotic habitats

Illies & Botosaneanu (1963) zonation Morphodinamic characteristics (slope, width, sediment granulometry) Temperature Community of benthic macroinvertebrates

CrenonEucrenonHypocrenon

RhithronEpirhithronMetarhithronHyporithron

PotamonEpipotamonMetapotamonHypopotamon

Discontinuities in macroinvertebratecommunities occur in those sectors wheremorphodinamic factors (flow, width, depth) change dramatically (mainly stream and river confluences).

The River Continuum concept (Vannote et al., 1980)

There is a gradient in the physicalfactors (morphology, hydrology) fromheadwaters to the esturary. Communities are in accordance withthis gradient.

There is an intimate connectionbetween river communities and thecatchment area due to the flow oforganic matter (input, transport, use by organisms).

Downstream communities dependon processes that occur in upstreamreaches.

Benthic macroinvertebrates presentdifferent biological strategies.

BiomarcadoresLotic habitats

BiomarcadoresLotic habitats

Primary production Allochthonous energy sources:

CPOM: Coarse particulate organic matter (e.g. tree leaves). FPOM: Fine particulate organic matter < 1 mm

Fragments of leaves and faeces DOM: Disolved organic matter

ENERGY RESOURCES

Tasa

de

carg

a de

car

bono

org

nic

o

Hynes (1975): The stream and its valley: the importance of watersheds on the functioning of freshwater habitats.

Primary production in lotic ecosystems

Prod

ucci

n p

rimar

ia re

lativ

a

BiomarcadoresLotic habitats

ALLOCHTHONOUS CPOM

Vegetal fragments of riverside vegetation.

Must be conditioned by bacteria and fungi.

Decomposition rate and nutritional value depend on the vegetal species.

CPOM input is higher in upstream reaches and decreases from headwatersto mouth.

BiomarcadoresLotic habitats

Physical mechanisms

Biological mechanismsFungi and bacteria: degradate cellulose

Shredders feed on CPOM

Collectors feed on FPOM

Grazers feed on peryphyton

Predators feed on the rest.

Degradation of the organic matter

Desmenuzadores

Food webs in lotic habitats

BiomarcadoresLotic habitats

River Continuum Concept (Vannote et al. 1980)

P/R < 1 High input of CPOM Riverside vegetation (shading) limitate instream primary

production Dominant organisms:

ShreddersCollectors

Headwaters (river order 1-3)

Mid-reach (river order 4-6)

Downstream reaches (river order>6)

BiomarcadoresLotic habitats

Less shading: higher primary production P/R>1 Dominant organisms:

ShreddersCollectors

High levels of FPOM and DOM Dominant organisms

Collectors Presence of planktonic communities