Qualidade da água em um reservatório da região semiárida após a reinundação - Dourado/RN

Abstract

Extreme events of prolonged drought can aggravate the symptoms of eutrophication, increasing the concentration of nutrients in water bodies. This is due to the low water level and intermittent rivers, which remain dry during this period, favoring internal fertilization, generating harmful consequences for the environment, the economy and public health. The northeastern semiarid has natural characteristics that make this region vulnerable to the eutrophication process. When the rainy season occurs, reservoirs that were dry or with very low volumes are flooded. This re-inundation event can result in an improvement in water quality or a deterioration due to erosion and nutrient input contribution from the watershed. Therefore, the objective of this work was to compare the water quality between two flooding periods in a tropical semiarid reservoir (Dourado), which was affected by water depletion events. The defined periods were: the period from April 2016 to March 2017 – after a 15-month water depletion – and the period from April 2019 to March 2020 – which was marked by the return of rains. The results in period II showed a reduction in the values of the variables turbidity, pH, electrical conductivity and reactive soluble phosphorus, when compared to period I, indicating an improvement in water quality in relation to these variables, resulting from the return of the rains. However, despite this, higher concentrations of chlorophyll-a were found, being sufficient to change the trophic state of the reservoir from mesotrophic to eutrophic. The other variables such as total phosphorus, dissolved oxygen and organic and inorganic suspended solids did not show a significant reduction compared to the previous period. Based on the results, it is possible to verify that there was no improvement in water quality after water renewal, due to the high values of total phosphorus and chlorophyll-a, showing a gradual eutrophication process. There is a need for attitudes towards the management and management of the reservoir and drainage basin for events that may happen such as prolonged droughts and heavy rains, so that you can have good water quality permanently or for a long-time duration.