Presentation on theme: "Lake (limnic) ecosystems Origins and classifications Lakes as open systems Light and temperature Lake chemistry Primary productivity Secondary."— Presentation transcript:
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: 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.
Small temperate lake fodwebs are detritus- based (e.g. Marion Lake). Predictions for Kamloops Lake?
Lake environment and community structure (North American boreal lakes) Environmental Fish assemblage factorPIKEBASSMUDMINNOW Arealarge -------------------- small pHhigh -------------------- low Conductivityhigh -------------------- low Depthshallow -- deep -- shallow Isolationlow -------------------- 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.
Lake evolution: Glacier Bay foreland, AK. Engstrom et al. (2000) Nature 408: 161
Stream and lake evolution: Glacier Bay foreland, AK. Source: Milner et al., 2007, Bioscience, 57, 237-247
Perturbations of lake environments 1. GEOLOGICAL local events such as landslides; regional events such as tephra deposition 2. CLIMATIC changes in regional climate (precip. or evap.) 3. ANTHROPOGENIC agricultural/industrial/urban pollution 4. BIOTIC invasion by exotic species (often anthropogenic)
Perturbation: tephra deposition into Opal Lake, Yoho NP Hickman & Reasoner (1994) J. Paleolimnology 11, 173-
Perturbations of coastal lakes on Vancouver Island
Reconstructing perturbations in lake environments using diatoms as a proxy for lake chemistry I: calibration based on 53 lakes in Ontario
II. Case study of anthropogenic pollution of Little Round Lake, Ontario. ~1850 ~1970
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 Physical habitat Biotic community Available species pool
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
Pool-riffle sequences and patchy lotic habitats
Blackwater rivers: terrestrial inputs are not always beneficial Kaieteur Falls, Guyana
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/