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.

Lakes as open systems

Kamloops Lake: inflow, water level and residence time variations

Thermal stratification of lakes: the physical properties of water

Thermal stratification of temperate lakes

Variations in epilimnion depth on windy and calm days

Seasonal temperature profile

Lake mixing types

Lake mixing types

Turbidity, illumination

, and the euphotic zone (--)

Kamloops Lake turbidity profile

Thompson R. inflowequilibrium level

Kamloops Lake:

euphotic zone and epilimnio

n

Biomass (= lake primary

productivity) in relation toP availability

Lake classification: trophic status

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

Kamloops Lake: relative abundance of phytoplankton

groups

Kamloops Lake: primary productivity

euphotic zone (Aug.)

euphotic zone (May)

Energy sources

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 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.

Lake infilling: Cedar Creek, Minnesota

Lake

evolu

tion:

Gla

cier

Bay f

ore

land, A

K.

Engstrom et al. (2000) Nature 408: 161

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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-

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

Physicalhabitat

Bioticcommunity

Available species pool

Str

eam

cla

ssifi

cati

on

Stream classification

Poff and Ward (1989)Can. J.Fish. & Aquat. Sci. 46, 1805.

Discharge regimes

Poff and Ward (1989)Can. J.Fish. & Aquat. Sci. 46, 1805.

Stream segment (reach)

classification and analysis

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.

RCC parameters

River continuu

m concept

in applicatio

n

Vannote et al. (1980)Can. J.Fish. & Aquat. Sci. 37, 130.

Headwater streams are

heterotrophic (P/R ratio

<<1); downstream reaches are

balanced (P/R ratio ~1)

Alpine-arctic

streams: dominantly autotrophic

RCC: boreal

streams

RCC: deciduous forest streams

Str

eam

ord

er,

nu

trie

nt

sou

rces

an

d F

FG’s

Stream nutrient cycling dynamics

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/