Lake Eutrophication

Eutrophication is the process in which lakes receive nutrients (phosphorus and nitrogen) and sediment from the surrounding watershed and become more fertile and shallow.  The additional nutrients are food for algae and fish, so the more eutrophic a lake is, the more living organisms it sustains.  When a lake becomes shallower from added sediment, even more plants can grow because the littoral area (the area of the lake that is shallow enough for light to reach the bottom) increases in overall percentage.  Eutrophication is a natural process that a lake goes through over hundreds to thousands of years.  Natural eutrophication is also sometimes referred to as lake aging.NaturalEutrophication

Humans can speed up the process of eutrophication by adding excess nutrients and sediment quickly, where the lake will change trophic states in a matter of decades.  This type of eutrophication is called cultural eutrophication because humans cause it.  Land practices such as agriculture, animal feedlots, factories and urban areas contain very concentrated amounts of nutrients.  These nutrients wash into lakes during heavy rains or through direct storm sewers.  The additional nutrients cause algal blooms, additional plant growth and overall poor water quality, making the lake less suitable for recreation. In addition, soil eroded by the removal of trees and vegetation washes into lakes, filling them in and making the bottom mucky.  When the lake becomes shallower, the percent littoral area (area of the lake shallow enough for light to reach the bottom) increases resulting in even more plant growth.

Eutrophication can be slowed if the inputs of nutrients (especially phosphorus) and sediment are slowed.  Land management goals for watershed should include identifying sources of eutrophication and reducing or eliminating them (more on how to slow eutrophication).CulturalEutrophication