Aquatic Sciences Meeting, Albuquerque 2001

PC07 Spatial and Temporal Connections

Date: Wednesday, February 14, 2001

Location: Southwest Hall

Elder, J, F, U.S. Geological Survey, Middleton, WI 53562, USA, jfelder@usgs.gov

Robertson, D, M, U.S. Geological Survey, Middleton, WI 53562, USA, dzrobert@usgs.gov

Goddard, G, L, U.S. Geological Survey, Middleton, WI 53562, USA, ggoddard@usgs.gov

SEASONAL, ANNUAL, AND LONG-TERM VARIABILITY OF NUTRIENT CONCENTRATIONS IN DELAVAN LAKE, WISCONSIN, IN RESPONSE TO NUTRIENT CONTROL PRACTICES

Recent management actions to reduce phosphorus concentrations and subsequent algal blooms at Delavan Lake in southeastern Wisconsin included, among other things, treatment of the lake sediments with alum, and expansion of a tributary wetland to remove phosphorus from inflowing water. Over the short term (monthly or seasonally), the actions were effective in reducing phosphorus concentrations. However, the immediate changes were normally followed by long periods of transition lasting several years, during which new conditions would gradually develop. Following the alum treatment, the lake-water phosphorus concentration decreased from more than 100 µg/l to less than 20 µg/l, but increased again over the next 2-3 years until it eventually approached previous levels. In the constructed wetland, part of the phosphorus load was removed over an annual time scale because of high retention capacity during the winter and early spring. But release of phosphorus was more common in the summer months, precisely when the potential for undesirable blooms was most prevalent. These observations illustrate short-term changes that often are not representative of longer-term responses over one-year or multi-year time scales.

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Aquatic Sciences Meeting, Albuquerque 2001

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