LAKEWATCH and EPA ’ s New Nutrient Criteria

Using data from 1387 lakes collected over three decades, we found a wide range in the concentrations of total phosphorus (TP), total nitrogen (TN) and chlorophyll in Florida lakes, and that edaphic factors as outlined by the USEPA’s Florida Lake Regions were the dominant factor in determining the concentrations of plant nutrients in the state’s lakes. The hypothesis that all eutrophic lakes in Florida are the result of nutrient pollution since European settlement of Florida that has led to significant increases in TP and TN in Florida lakes without point source pollution was tested and rejected. (1) There was no correlation between the Landscape Development Intensity index (LDI) and the concentrations of TP, TN and chlorophyll in Florida lakes. (2) Several of the 30-benchmark lakes (lakes with minimal human impact and meeting designated uses) were eutrophic and there was no significant difference between the concentrations of TP and TN in these and all the remaining Florida lakes as a group. (3) Paleolimnological studies showed that several lakes were eutrophic to hypereutrophic prior to 1900, a time before significant population growth in the state. Only 6 out of 39 lakes studied with short sediment cores showed increases in diatom-inferred total phosphorus and they were mostly the result of past point source pollution. We concluded that eutrophic lakes are a part of the natural Florida ecosystem and that numerical nutrient criteria need to take this into account. Table 1. EPA’s proposed nutrient criteria for lakes.