THE USE OF WETLANDS FOR NUTRIENT REMOVAL FROM SURFACE RUNOFF IN A COLD CLIMATE REGION OF CALIFORNIA - RESULTS FROM A NEWLY CONSTRUCTED WETLAND AT LAKE TAHOE

Pollutant removal by wetlands represents a potential mitigation technique for treating urban runoff in the cold climates of the Sierra Nevada. This is especially encouraging in the Lake Tahoe Basin, where research has demonstrated the link between nitrate and phosphorus, and a precipitous increase of algal growth in the lake. In September 1987 a plastic-lined, gravel-filled wetland was constructed for experimental purposes and is the first demonstration of its kind in a subalpine region of the western United States. The primary objective of our research was to evaluate the effectiveness of this system in removing nitrogen, phosphorus, iron, suspended sediments and other constituents from runoff. Data collected between August 1987 and March 1989 show that the average per cent removal of total Kjeldahl-N as it passed through the wetland was low at -3%. In contrast, nitrate concentrations declined by greater than +85-90%. Changes in particulate phosphorus concentrations between inflow and outflow decreased by +47%, however, the soluble-P component showed a -28% reduction due to a contamination of the gravel during construction. The reduction of iron was very high at +84% for total reactive iron and +78% for soluble reactive iron. Finally, both turbidity and suspended solids were removed by the wetlands at an efficiency of approximately +85%. © 1992 Academic Press Limited.