Lake (limnic) ecosystems Origins and classifications Lakes as open systems Light and temperature ...
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Transcript of Lake (limnic) ecosystems Origins and classifications Lakes as open systems Light and temperature ...
Lake (limnic) ecosystems Origins and classifications Lakes as open systems Light and temperature Lake chemistry Primary productivity Secondary productivity Lake evolution Perturbations
Lake classification: geological origin
Lakes result from impoundment of water by:Lakes result from impoundment of water by:• tectonic downwarping (e.g. Lake Victoria)• tectonic faulting (e.g. Dead Sea)• volcanic eruption (e.g. Crater Lake)• landslide dams• ice dams • biotic dams (e.g. Beaver lake)• glacial erosion (e.g. Lake Peyto)• glacial deposition (e.g. Moraine Lake)• river channel abandonment (e.g. Hatzic Lake)• deflation
Lake classification: morphology
• Lake morphology (size, surface area and depth) largely determined by origin.
• Substrate (rocky, sandy, muddy, organic) initially determined by geological origin; thereafter by inputs.
Lake classification: hydro-regime
• Open lakes have outflow streams.
• Closed lakes are found in endorheic basins in arid areas; e.g Lake Eyre (Australia): shallow lake forms in La Niña years (e.g. 2000), usually persists for 1 year. Never overflows - lake sits at 15m below sea level.
What is the trophic status of Kamloops Lake?
Total P: 4 - 10 µg l-1
Total N: 150 -250 µg l-1
Total inorganic solids: 60 mg l-1
TN: TP = 25 -35
Mean primary productivity = 88 mgC m-2 d-1
Lake environment and community structure
(North American boreal lakes)
Environmental Fish assemblagefactor PIKE BASS MUDMINNOW
Area large -------------------- smallpH high -------------------- lowConductivity high -------------------- lowDepth shallow -- deep -- shallowIsolation low -------------------- high
Lake evolution
1. All lakes are temporary features of the Erth’s landscape - eventually they fill with organic and inorganic sediments to become bogs or ‘playas’.
2. The pathway of lake evolution prior to infilling is a matter of debate. The classical European literature (1920’s -50’s) suggests that lakes progress from oligotrophic to eutrophic status. Pollution by agricultural fertilizers, etc. accelerates this process.
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Str
eam
and lake
evolu
tion:
Gla
cier
Bay f
ore
land, A
K.
Source: Milner et al., 2007, Bioscience, 57, 237-247
Perturbations of lake environments
1. GEOLOGICALlocal events such as landslides;
regional events such as tephra deposition2. CLIMATIC changes in regional climate (precip. or
evap.)3. ANTHROPOGENIC agricultural/industrial/urban pollution4. BIOTIC invasion by exotic species (often
anthropogenic)
Perturbation: tephra deposition into Opal Lake,
Yoho NP
Hickman & Reasoner (1994) J. Paleolimnology 11, 173-
Reconstructing
perturbations in lake
environments using diatoms as a proxy for
lake chemistry
I: calibration based on 53
lakes in Ontario
Stream (lotic) ecosystems
Controls on stream ecosystems Discharge regimes and biotic activity Segment/reach analysis Stream foodwebs The river continuum concept Nutrient cycling Patch stability and dynamics
Stream communities
• Physical structure• Flow dynamics
• Community organization
• Community dynamics
Physicalhabitat
Bioticcommunity
Available species pool
Str
eam
food
web
sallochthonous autochthonous
nutrientsources
functional feeding groups
POM = particulate organic matter (C =coarse; F= fine)DOM = dissolved organic matter
River continuum concept
• Continuous physical gradient from headwaters to mouth.
• Consistent biotic patterns of loading, storage and utilization of organic matter.
• Stream communities conform to the mean (most probable) state of the physical system.
• Biotic communities are graded downstream to accommodate leakage of organic matter from upstream.
Vannote et al. (1980) Can. J.Fish. & Aquat. Sci. 37, 130.
Stream hierarchy and patch (pool/riffle and microhabitat)
dynamics: complex habitats produce stable communities
Marine subsidies in riverine and riparian environments
Salmon streams: dead salmon add considerable quantities of marine-
derived N (22-73% of total N) to their natal streams. bears and other scavengers drag salmon
carcasses into riparian habitats; as a result (in AK-PNW):
15-30% of the N in riparian plant foliage is derived from marine sources; the amount declines with distance from the stream;
Sitka spruce grows 3x as fast adjacent to salmon streams but western hemlock shows no response;
annual variations in tree growth are significantly correlated with salmon escapements in riparian forests of the Pacific Northwest.
Notes derived from:http://www.fish.washington.edu/people/naiman/Salmon_Bear/