Most studies have focused on nutrient inputs from rivers, atmosphere, and nonpoint runoff. One often overlooked source of nutrient loading is submarine groundwater discharge. For this reason, a 207 site survey and four transects were established to document spatial distribution of macrophytes, quantify potential groundwater discharge and associated nutrient concentrations, estimate water column nutrient concentrations, and relate nutrient availability to seagrass stoichiometry. A significant decline in Thalassia testudinum and an associated increase in Halodule wrightii were significantly correlated with decreased salinity and increased ammonium and total phosphorus concentrations from surface and groundwater. Total phosphorus loading from groundwater was estimated to be 2.55 metric tons y-1 in the Black Point area, almost half the phosphorus load to all of southern Biscayne Bay from the canals. These findings indicate that nutrients in groundwater are important in determining seagrass community structure and spatial distribution in the shallow waters of Biscayne Bay.
