Capacidade de carga de fósforo de seis reservatórios da região semiárida brasileira

Abstract

The excessive enrichment of water bodies by nutrients and the increase in primary production is a natural process that happens slowly, however, this process has occurred in recent decades quickly, due to the increase in the external load of anthropogenic nutrients. Since phosphorus is considered the limiting nutrient for phytoplankton growth in lakes and reservoirs, the best way to control the effects of eutrophication is to control the intake of this nutrient in the system. In order to reduce this entry, models have been developed to calculate the maximum load of phosphorus, that is, their load capacity, but most of the models used do not consider the temporal variation of the volume occurring in reservoirs and lakes of semiarid regions. Therefore, this study estimated maximum phosphorus loads for six reservoirs in the Brazilian semiarid region, from a mass balance coupled to a water balance. This load is the maximum so that in 90% of the simulation period the concentration of phosphorus in the reservoir was up to 30 mg/m³, which is the limit established by law (CONAMA Resolution 357/05) for freshwater, in the remainder of the time the concentration could exceed the limit established. Scenarios with three vertical flow of phosphorus, four water demands, three initial concentrations and two initial volumes were simulated. The results showed that the parameters adopted in the simulations exerted a strong influence on the phosphorus loading capacity, with demand and vertical flow being the most influential. The incorporation of the volume level variation in the reservoirs, approached the simulations to the real situation of the region, demonstrating the importance of considering the temporal variability of the volume to obtain the reservoir load capacity of the semi-arid region.