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Lakes & Freshwater Wetlands
Lake – a depression in the Earth’s surface that collects and holds water
Can collect water from:- Streams and runoff that flows into them
- Local precipitation, springs, and other sources
Most lakes have outlets from which water flows out to rivers and streams
Origins of LakesForm naturally in surface depressions and low areas
Can form from landslides that block a stream
Can form from sinkhole that leaves a lake
Sinkhole lakes
Glaciers can form lakes when moraines block meltwater or water collects in cirques or other depressions left behind
Glacier lakes
Lake DevelopmentPlant’s add oxygen and wastes to lake water
Animals use the oxygen and add waste products
Decay of waste uses additional oxygen
Amount of oxygen determines a lake’s ability to support life
As nutrients change, lake organisms change
Run off of fertilizers and animal wastes can cause a rapid growth of algae
Overpopulation can use up the oxygen supply
WetlandsWetland – a land area that is covered with water for a large part of the year
Serve as a filtering system that improves water quality
Include bogs, marshes, and swamps
BogsReceive water from precipitation, not stream-fed
Rich in peat mossWater-logged, acidic soil supports unusual plants (pitcher plants and Venus’ flytrap)
Bog
Freshwater MarshesForm along the mouths of streams and in delta areas
Large deposits of silt and mudContains grasses, reeds, and abundant wildlife
Marsh
SwampsDevelop from marshes that have filled-in enough to support shrubs and trees
The shade kills marsh plants
Swamp