Water Quality and Eutrophication in Tampa Bay, Florida

A water quality model, WASP, was applied to simulate and evaluate the mechanistic relationships between external nutrient loading and water quality of Tampa Bay, U.S.A. The model quantifies processes governing internal nutrient cycling and phytoplankton growth. It estimates the impact of nutrient loads on water clarity, a pivotal water quality parameter for seagrass meadows. The model estimates impacts over long time periods and large areas, using tidally-averaged modelling: tidallyaveraged impacts were described by dispersion coefficients, calibrated with 1985-1994 salinities. These coefficients and monthly freshwater inflows were used to simulate both salinity and eight water quality variables. They involved four interacting systems: dissolved oxygen, phytoplankton, nitrogen and phosphorus concentrations. Model results were compared with monthly measurements and yearly-averaged estimates for 1985-1994. Tampa Bay was phosphorus enriched and nitrogen limited for algal growth. A component analysis indicated that the internal nutrient cycling and transport exceeded external loadings (external inputs from the watershed are the ultimate source of nitrogen). Cycling of nitrogen was governed primarily by phytoplankton, including growth, death and mineralization of organic-N.