1999-10-07_AgendaPacket - Laserfiche WebLink

Home

There are a number of concepts and terminology that are necessary to describe and evaluate a lake's water quality. This section briefly discusses those concepts, divided into the following topics: Eutrophication Trophic states ® Limiting nutrients To learn more about these topics, one can refer to any text on limnology (the science of lakes and streams). utr eca n Eutrophication, or lake degradation, is the accumulation of sediments and nutrients in lakes. As a lake naturally becomes more fertile, algae and aquatic plant growth increases. The increasing biological production and sediment inflow from the lake's watershed eventually fill the lake's basin. Over a period of many years, the lake successively becomes a pond, a marsh and, ultimately, a terrestrial site. This process of eutrophication is natural and results from the normal environmental forces that influence a lake. Cultural eutrophication, however, is an acceleration of the natural process caused by human activities. Nutrient and sediment inputs (i.e., loadings) from wastewater treatment plants, septic tanks, and stormwater runoff can far exceed the natural inputs to the lake. The accelerated rate of water quality degradation caused by these pollutants results in unpleasant consequences. These include profuse and unsightly growths of algae (algal blooms) and/or the proliferation of rooted aquatic plants (macrophytes). Tr iC t~tS Not all lakes are at the same stage of eutrophication; therefore, criteria have been established to evaluate the nutrient "status" of lakes. Trophic state indices (TSIs) are calculated for lakes on the basis of total phosphorus, chlorophyll a concentrations, and Secchi disc transparencies (Carlson, 1977). A TSI value is obtained from any one of these three parameters. TSI values range upward from 0, describing the condition of the lake in terms of its trophic status (i.e., its degree of fertility). Four trophic status designations for lakes are listed below, along with their corresponding TSI value ranges: grass_lake_intro.doc Page 1 09/27/99