Trend Analysis of Nutrient Concentrations and Loads in Selected Canals of the Southern Indian River Lagoon, Florida

Long-term nutrient concentration trends and load variations at six monitoring stations on four canals in the Southern Indian River Lagoon (Florida, USA) were evaluated using the Estimate Trend (Estrend) and Load Estimator (Loadest) programs. The results of trend analysis on nutrient concentrations suggested that the nutrient trend patterns were spatially variable. Increasing trends were most often observed in orthophosphate and/or total phosphorus at five stations. Significantly increased annual loads were observed for orthophosphate at four stations from 1979 through 2004. The median concentrations of ammonia (0.05 to 0.10 mg l^?1) were greater than the State of Florida surface water quality criteria of class III freshwater body for ammonia. The median concentrations of total phosphorus (138 to 376 μg l^?1) were greater than the USEPA ambient water quality criteria recommendation for the study area (Nutrient Ecoregion XIII). Nutrient (phosphorus and nitrogen) loads observed in this study are likely to impair the water quality in the Southern Indian River Lagoon.