lakes & reservoirs pt 1

formation: geological processes

• lakes are open bodies of still to very slow-moving water not in contact with the ocean

  • lentic systems

• most lakes are small, a few lakes are huge

• lakes most common in glaciated regions

lake types/ classifications

• lake origin & geology determine

  • basin area (basin= watershed= catchment)

  • shape/ depth of lake

  • minerals present:

    • sediment characteristics

    • water chemistry

• lakes are created by a variety of geologic and climatic events

how tectonic lakes form

• formed by movement of earth’s crust

• either a block slips down between two other, or diagonal slippage

how pothole/ kettle lakes form

formed when ice left from retreating glacier is buried in till and then melts

how moraine lakes form

glacial activity deposits a dam of rock and debris

how earthslide lakes form

movement of earth dams a stream or river

how volcanic- caldera lakes form

volcanic explosion causes hole that is filled with water

how dissolution lakes form

limestone dissolved and lake forms

how oxbow lakes form

river bend pinches off, leaves lake behind

tectonic lake basins

• faults and depressions created from crust movements

• the deepest lakes in the world were formed from fault movements (Tahoe, Baikal, Tanganyika, Malawi)

glacial lake basins

• most recent, ~14,000 years ago

• three common types

  • tarn/ cirque lakes

  • moraine lakes

  • pothole/ kettle lakes

• includes most of the lakes in the Great Lakes region and New England region

volcanic lakes

• crater lake- 589 m deep (mt. mazama exploded)

  • very low watershed to lake area ratio

• also caused by damming from lava flows

• characteristics:

  • steep sides

  • low nutrient soils

  • unproductive

  • extremely clear

landslide lakes

• quake lake, montana

  • formed on august 17, 1959 when a 7.5 earthquake caused a massive landslide that blocked the madison river

oxbow lakes

• more meandering rivers get pinched off

• shallow

• short lived

lake types based on nutrient

• oligotrophic lakes

  • deep

  • nutrient- poor

• mesotrophic

  • moderate amount of nutrients and phytoplankton productivity

• eutrophic lakes

  • shallower

  • increased nutrients

  • “cultural eutrophication”

    • pollution from fertilizers can cause explosions in algae population and cause a decrease in oxygen content

lake habitat stratification

• division by light penetration

  • littoral- shoreline to the depth of light penetration

  • limnetic- open H2O that receives light

  • profundal- portion of aquatic system where light doesn’t reach the bottom

  • benthic- interface between water and substrate

reservoirs

• man made lakes

• deepest by the dam

• take up the drainage basin of rivers and streams

• high value of shoreline development which means… highly productive unless too turbid

• continually fill in with sediment which limits their life span

• water levels controlled tightly for water storage, boating, hydroelectric power, species conservation, etc

• changing water levels make it hard for submerged plants to survive

standard model of lake evolution

modest- to small lake becomes a wetland then a meadow

shape of natural lakes & anthropogenic reservoirs

• predominantly circular to elliptical

• variable, often narrow, elongated, ovoid, dendritic, or triangular

mean depth of natural lakes & anthropogenic reservoirs

• moderate to high; average <10 m

• mostly moderate, rarely exceeding 30 m

depth gradient of natural lakes & anthropogenic reservoirs

• deepest usually remote from shoreline

• shallow in riverine portions, increasing toward transitional and lacustrine zones

drainage basin of natural lakes & anthropogenic reservoirs

• lake usually central or in higher portion of drainage basin; drainage area often small in comparison to lake area

• reservoir often at base of drainage basin; drainage area large in comparison to reservoir area

shoreline development of natural lakes & anthropogenic reservoirs

• relatively low; stable

• relatively high; astatic

sediment loading of natural lakes & anthropogenic reservoirs

• low to very low; deltas small, broad, gradation slow

• large with large drainage basin area; deltas large, channelized, gradation rapid

water- level fluctuations of natural lakes & anthropogenic reservoirs

• small; stable

• large; irregular

residence time of natural lakes & anthropogenic reservoirs

• often long, relatively constant (one to many years)

• often short, variable (days to several weeks); disruption of stratification with hypolimnetic withdrawal