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