Phosphorus, nitrogen, and the designated uses of Florida lakes

Abstract

We reviewed published information on the biology of Florida lakes to determine what concentrations of total phosphorus (TP) and total nitrogen (TN) might impair their designated uses. For the designated use of swimming, lake users preferred oligotrophic to mesotrophic lakes. Eutrophic lakes in Florida generally support their designated use of the propagation and maintenance of a healthy, well-balanced population of fish and wildlife. Fish standing crops in Florida lakes increased as the concentrations of TP increased from 1 to 1000 μg/L. Florida lakes did not show the kind of changes in fish species with trophic state as might be found in northern lakes. Populations of aquatic birds and alligators also increased with increases in trophic state. Benthic macroinvertebrate indices of lake condition were not related to anthropogenic nutrient pollution when estimated by the Landscape Development Intensity index. We found no evidence that the concentrations of TP and TN in the water were responsible for excessive populations of aquatic macrophytes. A study of open-water concentrations of the cyanobacterial toxin microcystin in 187 Florida lakes found only 3 individual water samples collected from 2 lakes exceeded the World Health Organization guidance level of 20 μg/L for swimming, although high levels of microcystin can sometimes be found in some lakes in surface accumulations of cyanobacteria.