The U.S. Environmental Protection Agency (EPA) developed numeric nutrient criteria (NNC) for Florida lakes by classifying the lakes and subsequently deriving chlorophyll a and nutrient criteria for each class. EPA based the classification on lake color and alkalinity thresholds it defined in January 2010. Researchers used available data on lake color and alkalinity for 82 lakes and computed their long-term average color.
Researchers used a weighted-lines-of-evidence approach to develop the final chlorophyll a criteria. The lines of evidence included trophic state of the lakes; existing conditions; estimates of natural background conditions in Florida lakes such as paleolimnological inferences, the state of the least disturbed lakes, and model predictions; and user surveys. Alkalinity, the state of the least disturbed lakes, and existing conditions were the primary lines of evidence used in establishing the chlorophyll a criteria. The percentile of the least disturbed condition used to inform the final criteria depended on lake class. All statistical data were based on Florida’s IWR/STORET database, which was developed by the Florida Department of Environmental Protection.
Final total nitrogen (TN) and total phosphorus (TP) NNC were determined both by lake class and by regression relationships between TN, TP, and chlorophyll a. EPA used trophic state and chlorophyll a to define thresholds, and derived criteria based on TP and TN from the response relationships of chlorophyll a to the nutrients (USEPA 2010b).
Reference:
USEPA. 2010b. Technical Support Document for U.S. EPA’s Final Rule for Numeric Criteria for Nitrogen/Phosphorus Pollution in Florida’s Inland Surface Fresh Waters. U.S. Environmental Protection Agency. Accessed October 2016.