Relação entre fósforo total e vazão afluente nos principais reservatórios rurais do estado do Ceará no semiárido brasileiro

Abstract

Water quality in interannual reservoirs in the Brazilian semiarid region is extremely important, mainly due to eutrophication, whose excessive nutrient input, notably total phosphorus, is a determining factor in this process. In this study, the behavior of the total phosphorus concentration was modeled as a function of the inflow in two serial reservoirs in the semiarid region of Ceará: Orós and Castanhão. Simplified models were proposed relating these variables through regression analysis. A water quality analysis was also carried out regarding compliance with CONAMA Resolution 357/2005 for total P and concentration values exceeded by 10% and 90% of the evaluated time, were obtained and discussed. Finally, a scenario analysis of the impact of different concentrations of total affluent P on the total P concentration in the water column of the reservoirs was performed. The results showed that the total phosphorus concentration presents a simple dilution regime in the proposed models (P <0.0001), responding inversely to the inflow. There was also a decrease in the concentration in the upstream reservoir compared to the downstream one, corroborating the results available in the literature for other regions. Finally, it was observed that the reservoirs were in disagreement with the Resolution for total P in 89.5% and 82.4% of the time analyzed in Orós and Castanhão, respectively, and that they do not reach the limit values for total P concentration for class II even though the inflow falls within the resolution for lotic environments.