Freshwater Aquatic Biodiversity 12/3/08

Freshwater systems May be standing bodies such as lakes, ponds, and inland wetlands May be standing bodies such as lakes, ponds, and inland wetlands Also may be flowing systems such as streams and rivers Also may be flowing systems such as streams and rivers Cover less than 1% of the earth’s surface Cover less than 1% of the earth’s surface

Lakes Large bodies of standing freshwater formed when precipitation, runoff, and groundwater seepage filling depressions in the earth’s surface Large bodies of standing freshwater formed when precipitation, runoff, and groundwater seepage filling depressions in the earth’s surface

Lakes 1. Littoral zone (top layer) is near the shore and consists of the shallow sunlit water Most productive zone because of sunlight and nutrient supply Most productive zone because of sunlight and nutrient supply High biological diversity High biological diversity 2. Limnetic zone—the open, sunlight water surface layer away from the shore that extends to the depth penetrated by sunlight Main photosynthetic body of the lake Main photosynthetic body of the lake Phytoplankton and zooplankton Phytoplankton and zooplankton

Lakes 3. Profundal zone—deep, open water where it is too dark for photosynthesis Low oxygen levels Low oxygen levels Many fish Many fish 4. Benthic zone—bottom of the lake Mostly decomposers Mostly decomposers Nourished by littoral and limnetic zones Nourished by littoral and limnetic zones

Lake temperatures During the summer and winter, water temperatures are divided by lake level During the summer and winter, water temperatures are divided by lake level In the fall and spring, the layers mix in overturns, which equalizes temperatures at all levels In the fall and spring, the layers mix in overturns, which equalizes temperatures at all levels Brings oxygen from surface layers to the bottom, and nutrients up to the top Brings oxygen from surface layers to the bottom, and nutrients up to the top

Seasonal changes in lakes

Plant nutrients and lakes Newly formed lakes have a small supply of plant nutrients—oligotrophic lakes Newly formed lakes have a small supply of plant nutrients—oligotrophic lakes Glaciers and streams supply clear water with low nutrient levels Glaciers and streams supply clear water with low nutrient levels

Plant nutrients and lakes Over time, sediment, organic material, and nutrients wash into the lakes Over time, sediment, organic material, and nutrients wash into the lakes A lake with excessive supply of nutrients needed by producers is called a eutrophic lake A lake with excessive supply of nutrients needed by producers is called a eutrophic lake

Plant nutrients and lakes Most lakes are in between the 2 extremes and are called mesotrophic Most lakes are in between the 2 extremes and are called mesotrophic

Streams and rivers Precipitation that does not sink into the ground or evaporate is surface water Precipitation that does not sink into the ground or evaporate is surface water It becomes runoff when it flows into streams It becomes runoff when it flows into streams

Watersheds The land area that delivers runoff, sediment, and dissolved substances to a stream The land area that delivers runoff, sediment, and dissolved substances to a stream Fig p. 160

Stream zones Source zone—mountain highland streams are shallow, cold, clear, and swiftly flowing Source zone—mountain highland streams are shallow, cold, clear, and swiftly flowing Lots of dissolved oxygen Lots of dissolved oxygen Not productive due to lack of nutrients and phytoplankton Not productive due to lack of nutrients and phytoplankton Populated by cold-water fish, such as trout, Populated by cold-water fish, such as trout,

Stream zones Transition zone—several smaller streams merge to form wider, deeper, and warmer streams Transition zone—several smaller streams merge to form wider, deeper, and warmer streams Less dissolved oxygen Less dissolved oxygen More producers More producers

Stream zones floodplain zone—streams join into wider rivers floodplain zone—streams join into wider rivers Higher temperatures and lower dissolved oxygen Higher temperatures and lower dissolved oxygen Fairly large Fairly large populations of producers Muddy with lots of Muddy with lots of silt due to erosion Often have catfish Often have catfish

Freshwater wetlands Lands covered with freshwater all or part of the time, and located away from coastal areas Lands covered with freshwater all or part of the time, and located away from coastal areas Includes: Includes: marshes (without trees), marshes (without trees), swamps (with trees), and swamps (with trees), and prairie potholes (small, shallow ponds in depressions carved out by glaciers) prairie potholes (small, shallow ponds in depressions carved out by glaciers)

Marshes

Swamps

Wetlands Plants are highly productive because of the abundance of nutrients Plants are highly productive because of the abundance of nutrients Habitats for a large diversity of species Habitats for a large diversity of species

Wetland benefits 1. Filter and degrade toxic wastes and pollutants 2. Reduce flooding and erosion by absorbing stormwater and releasing it slowly 3. Help replenish stream flows during dry periods 4. Help recharge groundwater aquifers

Wetland benefits 5. Help maintain biodiversity by providing habitats for a variety of species 6. Supply valuable products such as fish, shellfish, blueberries, cranberries, wild rice, and timber 7. Provide recreation for birdwatchers, nature photographers, boaters, etc

Wetlands in the United States 95% of the wetlands contain freshwater and are found inland 95% of the wetlands contain freshwater and are found inland Mostly in Alaska Mostly in Alaska More than ½ no longer exist (since the 1600s) More than ½ no longer exist (since the 1600s) About 80% were destroyed to grow crops About 80% were destroyed to grow crops

Human effects on freshwater systems 1. Dams, diversions, or canals fragment about 40% of the world’s 237 large rivers We alter and destroy habitats We alter and destroy habitats 2. Flood control levees and dikes built along rivers alter and destroy aquatic habitats 3. Cities and farmlands add pollutants and excess nutrients 4. Many inland wetlands have been drained or filled to grow crops or covered in concrete to build on