WATER-QUALITY TRENDS IN LAKE TOHOPEKALIGA, FLORIDA, USA - RESPONSES TO WATERSHED MANAGEMENT

Water quality in eutrophic Lake Tohopekaliga, Florida, improved marked ly from 1982 to 1992 as a result of reductions in phosphorus and nitro gen loading to the lake. Annual budgets of water, chloride, phosphorus and nitrogen were constructed for the lake, and indicate it is a sink for phosphorus and a source for nitrogen. Water column concentrations of total phosphorus, soluble reactive phosphorus, total nitrogen, dis solved inorganic nitrogen, and chlorophyll a all declined as external inputs of nutrients decreased. Water column nitrogen:phosphorus ratios have increased, suggesting a probable shift from nitrogen- to phospho rus-limitation. This apparent shift in nutrient limitation status also is supported by comparisons of the mean Trophic State Indices for pho sphorus, nitrogen, and chlorophyll a. These improvements in water qual ity are attributed to the diversion of wastewater treatment plant effl uent from the lake, and the increased use of wet retention ponds for s tormwater runoff.