An analysis of water column distributions in Florida Bay

Florida Bay is a shallow, semi-enclosed lagoon that has recently experienced significant changes to its ecosystem. These include increased turbidity and the occurrence of cyanobacteria blooms in the central region of the bay. To accurately understand these changes we need to understand the spatial and temporal patterns in observed water quality parameters. To this end, we have used empirical orthogonal functions (EOFs) to analyze both the spatial and temporal variability in an 8-yr record of water quality variables. We have used the EOFs in two ways, one highlighting local changes occurring in the bay, the other emphasizing changes occurring on a bay-wide scale. The local analysis shows that the central region of the bay has the greatest variability in water quality parameters, especially with respect to chlorophyll and nutrient concentrations. The bay-wide analysis shows a different picture. The chlorophyll blooms in the central bay are not apparent bay-wide indicating that they are a local manifestation of processes occurring on a bay-wide scale. The spatial and temporal patterns for nitrate are dissimilar from the other nutrients raising the possibility that the mechanisms controlling nitrate differ from those controlling other nutrients. On a bay-wide scale, spatial patterns are similar to distributions of sediment type and show the significance of interactions between the water column and benthos. Time-series analysis of the EOFs shows that the dominant variation of many water quality parameters is seasonal, even though a system-wide shift occurred between 1994–1995 corresponding to an increase in rainfall and runoff from the Everglades.