| Biscayne Bay, a tropical estuary along the southeastern Florida coastline, drains both the Miami metropolitan complex and South Dade Agricultural Area. Water management systems protect the watershed from seasonal floods but have also disrupted historical freshwater flows to the bay, which requires minimal phosphorus and nitrogen inputs. Watershed discharges therefore have a controlling influence on bay water quality and can degrade sensitive estuarine habitats.;To explore watershed land use and water quality variability, this study evaluated temporal and spatial land use influences on nutrient concentrations measured in canals discharging to Biscayne Bay. Disturbance indicators for 1995, 1999, and 2004 (landscape metrics, Landscape Development Intensity index [LDI], and imperviousness) suggested urban sub-basins were stable and characterized by complex residential areas, corresponding to greater anthropogenic intensity compared to agricultural and mixed land use sub-basins. Historical nutrient data (1992 to 2006), analyzed using multiple methods (trend analysis, load estimation, and a new water quality index), revealed water quality has generally improved. This improvement was likely a response to implementation of agricultural and urban best management practices as well as repair of leaky wastewater systems. The Pollutant Empower Density (PED) index assesses proportional impacts from point source discharges and two discharge locations (MW04 and LR06) had the greatest potential to degrade Biscayne Bay water quality. Land use and water quality relationships were evaluated at multiple spatial extents (sub-basins, canal buffers, and site buffers) and regressions suggested nitrate/nitrite-nitrogen loads were most related to land use variables at the sub-basin level. Development patterns in a smaller zone (1000 m canal buffer) were important factors for total phosphorus loads, reflecting watershed nutrient transport processes.;Rapid urbanization is ongoing in south Florida and both the intensity and spatial distribution of land uses affect nutrient discharges that could alter Biscayne Bay. Disturbance indicators can link land use to water quality parameters for improved watershed management, such as increasing treatment efficiency of established pollutant-control strategies (e.g., detention and retention systems) and guiding zoning regulations. Combined assessment of multiple indicators also provides a more holistic interpretation of water quality, which is necessary for optimizing resources to preserve water quality. |
