Food for plants turning lake from blue to green
March 26, 2003
Nutrient pollution occurs when phosphorus and nitrogen enter the lake in dissolved or particulate forms. These chemicals are commonly found in fertilizer. They are literally food for plants, including the algae that are beginning to turn Lake Tahoe green.
While fertilizer is beneficial to your landscape plants if your soils are poor, it is detrimental to the lake when it is carried off your property and into roadside ditches or nearby streams. Other sources of nutrient pollution include auto, factory and wood stove emissions; human and animal wastes; and fine sediments, which usually carry phosphorus with them.
Sediments are small and very small particles of eroded soil, including dust and pulverized road sand. When these particles are washed or blown into our streams and the lake, the larger grains settle to the bottom, but the tiny, fine particles remain suspended in the lake water. Since one of the main sources of phosphorus pollution is sediment, the control of soil erosion in the Tahoe basin has become a major priority of scientists and agency officials who are trying to prevent further pollution of the lake.
In the $2 million scientific study, the Lake Tahoe Watershed Assessment, water quality researchers blamed the steady loss of Tahoe’s famed water clarity on the combination of fine suspended sediment and equally tiny, single-celled algae, called phytoplankton, which are also suspended in the lake’s water and do not settle out. These algae will continue to grow in Lake Tahoe until we reduce the amounts of nutrients that feed them.
Since some nutrients and fine sediments enter the lake through air pollution, our basic strategy to save the lake’s clarity is to improve air quality in the basin while reducing the rate of soil erosion.
While pollution by pathogens and toxins are serious events when they occur, these problems are not widespread. Salinity and thermal pollution are even less often problems for the lake, although road de-icing salt can increase lake salinity in areas where road runoff and improperly stored snow can make their way into nearby streams or the lake itself.
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Watch for the Enviro Report in the Tahoe Daily Tribune each Wednesday and tune in to KOLO-TV Channel 8 Tuesdays at 5 p.m. to learn more. Next week learn about nonpoint source pollution and see how a watershed model is used to demonstrate this concept to kids. The Enviro Report is a collaborative effort of the Lake Tahoe Environmental Education Coalition, University of Nevada Cooperative Extension, UC Davis and the U.S. Forest Service. For more information, contact Heather Segale, University of Nevada Cooperative Extension, (775) 832-4138, or logon to http://www.lteec.org or http://www.unce.unr.edu.
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