Phosphorus and nitrogen inputs to Florida Bay: The importance of the everglades watershed

A large environmental restoration project designed to improve the hydrologi cal conditions of the Florida Everglades and increase freshwater flow to Fl orida Bay is underway. Here we explore how changing freshwater inflow to th e southern Everglades is likely to change the input of nutrients to Florida Bay. We calculated annual inputs of water, total phosphorus (TP), total ni trogen (TN), and dissolved inorganic nitrogen (DIN) to Everglades National Park (ENP) since the early 1980s. We also examined changes in these nutrien t concentrations along transects through the wetland to Florida Bay and the Gulf of Mexico. We found that the interannual variability of the water dis charge into ENP greatly exceeded the interannual variability of now-weighte d mean nutrient concentrations in this water. Nutrient inputs to ENP were l argely determined by discharge volume. These inputs were high in TN and low in TP; for two ENP watersheds TN averaged 1.5 mg 1(-1) (0.11 mM) and 0.9 m g 1(-1) (0.06 mM) and TP averaged 15 mu g 1(-1) (0.47 mu M) and 9 mu g 1(-1 ) (0.28 mu M). Both TP and DIN that flowed into ENP wetlands were rapidly r emoved from the water. Over a 3-km section of Taylor Slough, TP decreased f rom a flow-weighted mean of 11.6 mu g 1(-1) (0.37 mu M) to 6.1 mu g 1(-1) ( 0.20 mu M) and DIN decreased from 240 mu g 1(-1) (17 mu M) to 36 mu g 1(-1) (2.6 mu M). In contrast, TN, which was generally 95% organic N, changed li ttle as it passed through the wetland. This resulted in molar TN:TP ratios exceeding 400 in the wetland. Decreases in TN concentrations only occurred in areas with relatively high P availability, such as the wetlands to the n orth of ENP and in the mangrove streams of western ENP. Increasing freshwat er now to Florida Bay in an effort to restore the Everglades and Florida Ba y ecosystems is thus not likely to increase P inputs from the freshwater Ev erglades but is likely to increase TN inputs. Based on a nutrient budget of Florida Bay, both N and P inputs from the Gulf of Mexico greatly exceed in puts from the Everglades, as well as inputs from the atmosphere and the Flo rida Keys. We estimate that the freshwater Everglades contribute < 3% of al l P inputs and < 12% of all N inputs to the bay. Evaluating the effect of e cosystem restoration efforts on Florida Bay requires greater understanding of the interactions of the bay with the Gulf of Mexico and adjacent mangrov e ecosystems.