| The nutrient state of the surface water is a very important issue. The objective of this study was to evaluate the nutrient state of the surface water of five rivers in the Rio Grande de Arecibo Watershed and the impact of possible pollutants sources of total phosphorus (TP). Thirty three stations operated by the United States Geological Survey (USGS) were evaluated, 9 of them showed TP values over 0.1 mg/L, the suggested level to indicate pollution in rivers. Five small watersheds located in areas with high levels of TP were monitored for 6 months. Measured parameters were TP, total Kjeldahl nitrogen (TKN), dissolved reactive phosphorus (DRP), suspended sediments (SS), pH, conductivity, total coliforms (TC) and chlorophyll a (Chl-a). Using the water quality data, water discharge (Q) and the contributing area, TP export coefficients were calculated for each small watershed studied. The results showed mean concentrations of TP, DRP, TKN and TC higher in watersheds with animal production landuse and high percentage of urban landuse. Highly significant correlations between TP and SS and TC were observed, which suggested that the movement of these pollutants occurred by similar transport mechanisms. The concentration of TP correlated significantly with Q showing the relevance of non point sources on the watersheds studied. The export coefficients estimated were 1.84 and 1.45 kgTP/ha/yr exported for subbasins with animal production landuse, and 0.68, 0.70 and 0.28 kgTP/ha/yr for areas with small sections of urban landuse. Areas with high concentration of animals represent a significant P source to surrounding waters. |
