AVALIAÇÃO DA QUALIDADE DA ÁGUA E DO SEDIMENTO EM RESERVATÓRIOS DE ABASTECIMENTO PÚBLICO NA BACIA DO RIO MAMANGUAPE, PARAÍBA, BRASIL

Abstract

Eutrophication is currently one of the greatest environmental impacts worldwide, proven and present in northeastern waters. Due to this process many water bodies in the world have already lost the capacity of human supply, maintenance of aquatic life and recreation. Phosphorus, a nutrient limiting to eutrophication, comes mainly from domestic sewage, industrial effluents and fertilizers. In addition to its presence in the water column, the external contribution of this nutrient can be deposited in different forms at equal or even higher intensities. The objective of this work was to monitor the water quality and the phosphorus content in the water and sediment of three reservoirs of public supply in the city of Areia - Paraíba, generating information to diagnose the main impacts on these environments. In order to do this, monthly samples of water were collected and sediment samples annually. Some parameters such as pH, electrical conductivity, temperature and transparency were analyzed in situ. At the laboratory, total phosphorus, orthophosphate content in water and the fractionation of phosphorus forms in the sediment were analyzed. It was observed that the seasonality influenced the parameters of water quality, mainly the conductivity and the pH. In most of the analyzed months, the reservoirs presented as oligotrophic, with low values of P-total and orthophosphate in the water. P-total contents in the sediment ranged from 1185.3 mg kg-1 to 3182, 1 mg kg-1. The fractionation indicated predominance of the inorganic P reaching 86.8% of the total phosphorus in the Rio do Canto dam in 2014. The apatite and unavailable fraction was predominant in the inorganic phosphorus. It was observed low pH levels in the sediment, which favors the adsorption of non-apatitic phosphorus and available, with iron and aluminum, retaining it. It was concluded that seasonality is a determining factor in the water quality variation of these reservoirs. The results indicated a potential natural control in the release and increase of the phosphorus concentrations of the sediments to the water column, reducing the effect of eutrophication on the waters of the reservoirs of that region.