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Summary Freshwater Ecology - VUB - 2023/2024
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Summary of all lectures of the course Freshwater Ecology, given by professors Kristien Brans & Iris Stiers
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• Limnology = lakes, rivers, wetlands→ Lentic (standing) / lotic (streaming)
→ Freshwater / brackish / saline
• Studies about…
→ Energy flux, nutrient flow, P-limitation, nutrient flow, food web
interactions, functional groups…
• 1922: Einar Naumann = founder of the Societas Internationalis Limnologiae
→ Introduced the terms “oligotrophic”, “eutrophic” and “dystrophic” for
lake classification
• 1956: Hutchinson & Löffler: classification based on mixing regimes
→ Thermal stratification = layering (water bestaat uit versch lagen qua
T°) → dimictic, monomictic…
→ See further
• Deep/large lakes vs shallow/smaller water systems = close interaction between
organism, water and sediment
→ Stratification
→ A lot is man-made
• Well-watered Northern temperate regions vs Tropical systems
→ Tropics:
▪ older water systems (stable climates)
• no short/long days
• no seasonality
• higher T°
▪ higher productivity
▪ higher biodiversity
▪ more plank./omni.fish & shrimps
→ Temperate:
▪ more algivorous invertebrates & zooplankton
• Undisturbed catchment vs Antropocene (climat change)
→ Urbanization, industrialization, agricultural intensification… lead to:
▪ Warming, rising pCO2, hydrological change (damming/extraction), salinization, pollution,
eurtrophication, introduction of exotic species
• Importance of scale
→ Temporal
▪ e.g.: larger organisms = more time needed to reproduce
▪ e.g.: climate change = changes over years and not seen in couple of days
→ Spatial, e.g.: community (eg rivers) vs individual (eg part of a plant)
• Multiple disciplines needed to understand changes in an ecosystem
• Increased attention:
→ Ecosystem functions:
▪ Carbon emission/sequestration, hydrological balance, pollution retention, etc.
→ Ecosystem (dis)services :
▪ Water provisioning, food provisioning, aestethic/psychological, disease spread, etc.
• Hierarchy of properties and attributes: ecoregions (ecological
zonation)
→ Regional properties
▪ Climate, geology, topography
→ Catchment attributes
▪ Vegetation, soil, hydrology
→ System attributes
▪ Morphometry, lake stratification, flushing rate
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, → Physical/chemical water properties
▪ Light (photoperiod), temperature, turbidity, salinity, discharge, humic substrates, nutrients, toxins
→ Biological/ecological properties
▪ Biomass, productivity, trophic structure, biodiversity
→ As well: human impacts
▪ See previous page
THE EARTH IS A BLUE PLANET
• 71% of surface = water
• 1.4 billion km3
• 97% oceans
• <3% freshwater
→ Most in form of glaciers (76%)
→ Groundwater (23%)
→ Lakes, rivers, wetlands (0.3%)
CONFLICTS WITH WATER USE
• >99% freshwater = NOT available for consumption!
• Water footprint humans: 7000 L.head-1.day-1 in industrialized countries (8.6 – 2.9)
GLOBAL DISTRIBUTION OF FW LAKES AND WETLANDS
• Wetlands
→ Boreal forests and subarctic region
→ Equator
• Freshwater lakes > 100 km2
→ 40-50° latitude N/S
→ Equator
• 8-9 million (real) lakes
→ + 20 lakes very deep/large
→ Only 3 are >1000m deep: Lake Baikal, Tanganyika, Caspian Sea
→ Most are small / shallow
▪ 117 million lakes in reality, but very small + dry out or temporary
→ Vary in size
▪ (Glowabo = global water boundaries)
→ + 20% of world’s freshwater (excl. ice) is in Lake Bailkal
• What is a large lake?
→ How many water?
→ Surface area + depth?
THE MAJOR LAKES (know them + location)
➔ Largest (SA + volume) inland water basin : Caspian Sea
➔ Greatest continious mass of freshwater : Great Laurentian Lakes
(N-Am) = Superior, Michigan, Huron, Erie and Ontario
o 21% FW on earth + are connected to each other
o Provided with water via: streams (rivers,…) (‘feeds’)
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,HYDROLOGICAL CYCLE
• W = water content in 103 km3
• Tau = retention time
• °lakes = via evaporation of mainly the ocean (448) +
precipitation on land (100)
→ Precipitation → (sub)surface run-off and groundwater
→ °lakes
• 2/3rd from continents to atmosphere + 1/3rd to oceans
• The importance of vegetation
→ Infiltration → harder for the water to get back in the atmosphere
→ Soil stabilization
→ Transpiration (+ reduction in runoff)
→ River flushing = a sudden significant increase in flow
▪ E.g. due to high-intensity storms of short duration, fast ice melting…
▪ Consequence: temporary increase in the river’s discharge (afvoer) (peak in graph)
▪ BUT, when vegetated = reduced peak discharge!
• Vegetation absorbs water partially
1) EXORHEIC or OPEN BASIN LAKES
• “Exolake”
• Outflow (via rivers,…)
• Usually freshwater
• Europe:
→ Low surface evaporation
→ More or less stable water volume
• Low precipitation, low latitude, semi-arid or seasonally arid zones:
→ High evaporation losses
→ Low precipitation
→ Outflow can be blocked (0 discharge local streams)
→ Variable lake water volume in shallow lakes or seasonal wetlands
▪ Can become saline due to this (naturally or human-induced)
2) ENDORHEIC or CLOSED BASIN LAKES
• No stream or subsurface outflow
• Closed
• Precipitation, inflow and evaporation
• Usually more saline than exolakes (built-up of salts and minerals because no escape) (e.g. salt mining)
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, 3) TRANSITIONAL LAKES
• Oscillate between open/closed as result of change in climatic conditions
• Rise in salinity during dry periods and vice versa during wet periods
ANTHROPOGENIC IMPACTS: LAKE ARAL
• Agricultural intensification: lake = along the Silk Route → drainage for cotton (and other crops) plantations
• 4th largest lake of the world
• Endorheic, 68.000 km2
• Soviet era
• Dessert irrigation
• Re-routing of source rivers + inefficiency
(water loss)
• Pollution: pesticide use and weapon testing
• Fisheries: societal drama (40% fish production SU)
• Salinization (x10): loss of biodiversity + salty groundwater
→ Bad for human health
• More dust in the air = bad for health as well
• Consequence: Lake Aral does not exist anymore…
→ North Aral Sea: resoration efforts
→ South Aral Sea: continued degradation/loss
Other examples
• Shrinking colorado river in W-N-Am (mainly drought)
• Ogallala Aquifer in Texas: will dry up in this century as well
AGE AND ORIGIN
• Determines lake morphology
• Affects major physical properties
→ Turbulence (windaction)
→ Water T°
→ Stratification
→ Productivity
• Important with respect to lake biology
TYPES OF FROMATION
• Glacial: most lakes < glacial action (ice movements and glacial retreats)
→ A lot of young (<10 000 yo) lakes after last Ice Age (melting) e.g. Bodensee, Lake Geneva
• Coastal lakes: recent (present sea level stabilized only about 6000 ya)
→ Only a few lakes
• Tectonic/volcanic lakes: extremely deep
→ 2-20 million yo = very old!
• Many lakes of biotic/organic (animal/plant) origin or man-made, many systems shallow/small (see further)!
• Fluvial: lakes at low latitude filled by rivers at higher latitudes
• Solution lakes = e.g. Karst lakes (dissolution of limestone, gypsum…)
• Meteoric lakes
• Landslide lakes = lake formed by landslide-damming
(due to erosion…)
• Aeolian lakes = in a depression within sand dunes due
to wind action and aeolian processes ((semi)-arid
zones)
→ Can be temporary or seasonal
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