NUTRIENT DISTRIBUTION AND VARIABILITY IN THE CHARLOTTE HARBOR ESTUARINE SYSTEM,FLORIDA1

ABSTRACT: The sources and distribution of nutrients in the Charlotte Harbor estuarine system were evaluated using nutrient dilution curve models. Except for ammonia, nutrient concentrations were highest and most variable in the rivers, and generally decreased with increasing salinity. Observed and theoretical dilution curves for phosphorus were generally in close agreement, which suggests conservative behavior. Phosphorus concentrations sagged below a straight line because phosphorus-rich water from the upper Peace River basin was diluted by tributaries in the lower basin. The concentrations of dissolved silica appeared to be conservative on some occasions. On other occasions, dissolved silica appeared to be removed at low salimties or released at higher salinities. Concentrations of ammonia were highly variable along the salinity gradient, presumably because of variations in ammonia regeneration and uptake. Concentrations of nitrite plus nitrate were well below conservative dilution curves, probably due to phy-toplankton uptake. At salinities greater than 20%, nitrite plus nitrate concentrations were usually at or below the detection limit and may limit phytoplankton productivity. Projected increased nitrogen loadings from urban development in the basin would favor undesirable increases in phytoplankton and benthic algal growth in waters where sufficient light is available.