Environmental characterization and impacts of fish farming in the cascade reservoirs of the Paranapanema River, Brazil

Abstract

The goal of this study was to characterize current water quality, simulate water quality in 8 large artificial reservoirs occurring along the course of the Paranapanema River, Brazil, and estimate fish production in the region to assess the impacts of this production on the local aquatic environment. Primary data describing the bottom sediments and water quality, and time series recorded between 2001 and 2011 were used. Water quality was modeled to simulate the trophic state index (TSI) for each reservoir, and 37 fish cage farms along the length of those reservoirs were identified. Only one-third of these farms had environmental licensing for regular operations. The potential increase in fish production was estimated to exceed 250% in the short to medium term. The concentrations of nutrients (organic matter, nitrogen, and phosphorus) present in the bottom sediment beyond areas of fish production were similar to those found in areas distant from the fish farms. The TSI results indicated that the reservoirs could be classified between oligotrophic and mesotrophic. The few eutrophied areas represented approximately 1% on average of the total area of the reservoirs. The reservoirs of the Paranapanema River have adequate water quality standards for aquaculture, and there is no indication that this activity is currently causing significant impacts to the overall aquatic environment in each reservoir. Nevertheless, caution is required when selecting areas for new fish farms to avoid areas that are more susceptible to eutrophication.