Environ 303 LAKES Exam Review

why origin and morphometry are important

- role in physical, chemical and biological processes

- controls drainage, nutrient inputs, volume of influx in relation to flushing-renewal times

- influences distribution of dissolved gases nutrients, organisms, productivity

lake's metabolism

turnover of biomass and energy in lake ecosystems, describes how much organic matter is produced by plants/ other organisms and then consumed by other organisms

productivity

rate at which organic matter is produced within a lake. deep steep sided or V shaped basins have LESS water contact with sediments and are LESS productive than shallow depressions

tectonic lakes

depressions formed by movements of deeper portions in the earth's crust (OLDEST lakes) ex: graben lakes, african great lakes, lake baikal, lake thingvallavatn

volcanic lakes

lakes that form in depressions on volcano peak or slope (craters, calderas, maars, pit craters) or lakes that form due to lava flow (dammed river valleys, lake basins)

maar

stream explosion when magma superheats groundwater

pit crater

part of volcanic surface collapses/sinks

lake basins

discontinuity of lava flows

lava tube lakes

collapsed tunnels

lava flow dams

barriers created when lava flows into river valleys blocking water flow

landslide lakes

large landslides can block rivers and create lakes in the mountains, vulnerable to overtopping

subglacial lakes

lakes under ice

supraglacial lakes

lakes on ice

glacial scour

depressions carved out by glaciers

morainic/outwash lakes

lakes created on/by terminal, recessional, lateral moraines

kettle lakes

large block of ice that falls off a glacier and melts, forming a hole then filling with water

tarn lakes

mountain lake, formed in a cirque which is a bowl-shaped depression carved out by glacier

continental scour lakes

formed when large continental ice sheets erode and carve out depressions in the Earth's surface

lakes formed by solutions processes

soluble rocks are slowly dissolved by percolating water, majority formed from a solution of limestone, slightly acidic water, and contact with atmospheric CO2

collapse sinkholes

develop by collapse of material into an underground cavern, groundwater dissolve rocks below surface

solutional sinkhole

dissolution at surface

sinkhole-controlled lakes

characterized by sinkholes in the lake basins which control the lake level

fluvial lakes

produced by aggradation of sediment by running water (meander lakes, plunge pool lakes, fluviatile dams) FORMED BY ACTION OF RIVERS/STREAMS

aeolian lakes

water-eroded basins, formed by wind-blown sand deposits

shoreline/coastal lakes

form when wind and waves isolate lagoons along the coasts

organic lakes

caused by the activities of living organisms

anthropogenic lakes

man-made lakes (reservoirs, ornamental lakes, mines/quarries)

water balance (sources/ losses)

lakes reflect their watersheds (soils, vegetation, land uses) and climates. morphometry and hydrology are determinants of how lake functions

water balance

the balance between water intake and water excretion, keeps the body's water content constant.

change S = rate(sources) - rate(loses)

lake sources

precipitation, surface influents of drainage basin(streams, runoff), sublacustrine groundwater seepage and springs

lake losses

evaporation directly from lake surface, transpiration from plants, flow from an outlet, seepage into the groundwater

open lakes (exorheic)

have an outflow

closed lakes (endoheic)

have NO outflow

vertical and horizontal zonation

layers of waters due to density differences is a major factor structuring the ecosystem and creating distinct habitats

temperature of lakes

- bottom water is colder than surface water in the summer, a bit warmer in the winter

- surface water is buoyant because of large density difference between it and cold bottom water, leading to thermal stratification

thermal stratification

tendency of lakes to form separate and distinct thermal layers during warm weather

dissolved oxygen

-vertical distribution of dissolved gases -> lakes are not "well-stirred like rivers

-similar to that in rivers but varies spatially, temporally, with productivity, temperature(solubility increase, temp decrease), depth

mid summer dissolved oxygen

STRONG thermal stratification

-surface water (epilimon) too warm

-bottom water (hypolimnion) onoxic

forced in suboptimal

summer fish kills

usually during periods of high temps, little wind, high cloud cover

winter fish kills

ice cover remonds aeration, snow cover limits photosynthesis under ice

light in lakes

water depth strongly influences aquatic life because sunlight penetrates only a relatively short distance. the absorption and attenuation of light by the water column are factors controlling temperature and photosynthesis, which provides dissolved oxygen. influenced by depth, clarity, ice cover, waves, sun angle

photic zone (euphotic)

solar irradiance is >1%, photosynthesis is greater than the rate of respiration by phytoplankton, upper portion receives sunlight; high DO, dense fish population

compensation point

where photosynthesis = respiration, lower limit of photic zone, maximum depth at which algar and vascular aquatic plants grow

aphotic zone (profundal)

solar irradiance <1%, respiration > photosynthesis, deep water, sun does not penetrate, low DO many parts of the year, low fish population

distance from shoreline(horizontal)

transitional zones from the shore to the deepest point-distinct zones of biological communities linked to physical structure of lake

littoral zone

near shore area, shallow, sun penetrates all the way to sediment. nutrient and macrophyte abundant

limnetic (pelagic) zone

the open water beyond the littoral zone, where the dominant photosynthetic organisms are floating algae. two zones: euphotic and profundal. nutrient poor

benthic zone

bottom of aquatic ecosystem; consists of sand and sediment and supports its own community of organisms

oligotrophic

deep clear water, low nutrient levels, concentration of dissolved gases determined by atmosphere rather than photosynthesis/respiration, limited life

mesotrophic

middle, medium amount of nutrients. stratified: top layer -> warm, algae, high oxygen. bottom layer -> cooler, anoxic(depleted O2), fish move shallower in lake summer

eutrophic

nutrient rich, murky water, soft bottoms, abundant plants/life, high biomass -> high decomposition at bottom.

bottom layer: anoxic all year. top layer: photosynthesis -> abundant oxygen

influential factors of trophic states

1. rate of nutrient supply (bedrock geology, soils, vegetation, adjacent land uses, atmospheric deposition)

2. climate: sunlight, temperature, seasonality, precipitation

3. morphometry: size/depth

eutrophication

human activities -> spike in nutrient levels, algal blooms, increase DO near surface, increase amount of life in lake, reduced DO at bottom, fish kill

oligotrophication

process of nutrient depletion, or reduction in rates of nutrient cycling, in aquatic ecosystems.

SUMMER EXAMPLE

temperature: warm at surface, sharp drop at 4-8m

DO: relatively high near surface

pH: gradual decrease in hypolimnion, respiration exceeds photosynthesis. LOWER pH

seasonal mixing

summer: strong thermal stratification

winter: weaker inverse stratification

lake turnover

seasonal mixing of the entire water column due to density differences

- spring and fall: both oligotrophic and eutrophic lakes tend to have uniform, well-mixed conditions. biological activity peaks in summer

exceptions to typical turnover

tropical climates, violent storms, streams/waterfalls, inconsistent turnover, partial freezing

classifications

amicitic: no mixing

holomicitic: complete mixing at least once

meromicitic: permanently stratified or interruption of stratification patterns at irregular intervals

oligomicitic: rarely overturn

reasons lakes disappear/die

infilling with sediment, drying out, draining, glaciation, submersion

sediment archives

water quality history, volcanic history, climate history