Frações de fósforo do sedimento límnico e sua mobilidade em reservatório da região semiárida tropical

Abstract

Phosphorus is a crucial nutrient for the aquatic environment, however its excess has brought imbalance to the lake ecosystem. The mobile forms of phosphorus in the sediment are the available fractions that will be released into the water column for assimilation by primary producers. In this context, the nutrient phosphorus contributes to the eutrophication process, which results in the excessive and disordered growth of primary producers. Thus, the objective of this work is to identify and quantify the phosphorus fractions that favor the release and retention of phosphorus in a reservoir in the tropical semi-arid region. Thus, fractionation analysis, through sequential chemical extraction and spectrophotometry were performed to determine the P fractions in the sediment of the Dourado reservoir/RN. From the results, the highest phosphorus concentrations were the mobile inorganic fraction of P adsorbed to Iron and Manganese oxides (P-BD) and the non-mobile inorganic fraction of P adsorbed to Aluminum oxides (P-NaOH), indicating that these fractions can potentially be released into the water column, with the non-mobile fraction (P-NaOH), released at alkaline pH, this release is induced mainly in lakes with hot and arid climates. In this scenario, organic P also contributes to the internal load, as P is released when autochthonous organic matter is mineralized at the sediment-water interface. On the other hand, the non-mobile fractions of phosphorus adsorbed to calcium (P-HCl) and phosphorus adsorbed to humic substances (P-Humics) analyzed in the sediment of the Dourado reservoir showed very similar values and are stable fractions that are difficult to release. Finally, this study suggests that mitigation techniques for the eutrophication process in these environments are necessary, taking into account the internal load to effectively reduce the problem of water quality degradation in several lakes with a high level of trophy and that experience long periods of drought.