The influence of aquaculture on the hydro-geochemistry of a neotropical aquatic system

Abstract Pollution in the aquatic ecosystem is a central theme in ecological research. We investigated the hydrogeochemical characteristics of the Sa?o Francisco Verdadeiro River, a tributary of a Neotropical reservoir, which is under a strong influence of local agricultural, industrial and urban activities, and direct influence aquaculture in its tributary. Conventional water quality parameters were monitored bi-monthly in the hydrological cycle at seven longitudinal sites. Consistent with the expected pattern, nutrient concentrations were higher for the points (mouth of small creeks from cities and/or agricultural regions) S1, S2 and S4, with TN values of 5.37×10−1, 7.99×10−1 and 8.88×10−1 mg L−1 respectively. Similar behavior presented in the TP contents, with values of 9.66×10−2, 1.51×10−1 and 1.14×10−1 mg L−1 respectively were observed. All parameters were also analyzed by the Principal Component Analysis (PCA), showing similarities between S1, S2, and S4 (more nutrient concentrations) and S3, S5, S6, and S7 (fewer nutrient concentrations). Our findings suggest that the aquaculture activity in fish-cages is not impacting the environment. Conversely, there is strong evidence of punctual and diffuse pollutant sources that contribute significantly to the increase of nutrients in the water, mainly those in the nitrogenate and phosphate forms, resulting in the deterioration of the water quality. The results indicate the need for an integrated management of the river basin aiming at maintaining the environmental quality.