Evaluating Spatial Variability of Florida Lake Water Quality Using Clustering Analysis and Water Quality Index

This study evaluated the spatial variability of water quality of Florida lakes at two spatial scales, i.e., the state scale (for 852 lakes) and the watershed scale (for 2 lakes). At the state scale, the concentrations of total nitrogen, total phosphorus, and chlorophyll a were compiled from the Watershed Information Network for the period of 2012–2024, which led to a dataset of 14,403 records for 852 lakes across Florida. Four clusters were identified, and their average (over space and time) concentrations of total nitrogen, total phosphorus, and chlorophyll a correspond to the four eutrophication conditions (hypereutrophic, mesotrophic, eutrophic, and oligotrophic states) used by the Florida LAKEWATCH program. The clusters do not exhibit spatial patterns, indicating that lake water quality is controlled by variables of local variability such as land use and watershed runoff conditions. To evaluate spatial variability of lake water quality at the watershed scale, this study collected water quality data for a comparison of Lake Munson (an urban lake) and Lake Bradford (a rural lake) located in Lake Munson watershed, FL. The data included weekly sampling in November 2024 and historical data for the period of 2016–2023 collected by the Leon County. Based on the data, the Water Quality Index (WQI) defined by the National Sanitary Foundation was calculated for the two lakes. Although Lake Munson and Lake Bradford receive runoff from urban and rural areas, respectively, the two lakes had similar WQI-based water quality grades. The results of this study may indicate that lake water quality is controlled by variables of the watershed scale, which may be useful for effective and efficient lake management.