Avaliação da qualidade das águas subterrâneas do aluvião do Rio Sucurú, Sumé – PB, quanto ao risco de salinização e sodificação.

Abstract

The Brazilian Semi-arid Zone - BSZ, due to high evaporation rates and growing water demands, stands out as the area with the greatest occurrence of water scarcity, considering both qualitative and quantitative aspects, with increasing conflicts over water use. Small alluvial deposits formed in riverbeds over crystalline bedrock play an important role in supplying water for agricultural production and animal watering. The objective of this study was to assess the water quality of wells located in the alluvium of the Sucurú River, in the municipality of Sumé, PB, for use in irrigation and animal watering, as well as to evaluate the impacts caused by diffuse pollution. The study area is located downstream of a public reservoir with a capacity of 45 hm³, in a section of the Sucurú River alluvium, which covers 351 hectares, has a width ranging from 50 to 500 m, a depth of 0.5 to 15 m, and an estimated storage capacity of 1.7 hm³. This section receives treated and untreated urban domestic sewage discharge. To classify the groundwater, eight Amazon-type wells were selected, located upstream, in situ, and downstream of the urban zone of the municipality. Due to the multiple uses of water, underground reserves are fundamental for all Sustainable Development Goals – SDG, with particular emphasis on SDG-6. Physicochemical parameters of water quality were obtained, and the sodium adsorption ratio - SAR was calculated based on the concentrations of sodium, calcium, and magnesium, combined with electrical conductivity (EC) values. This classification aimed to determine the water's risks of salinization, sodification and suitability for animal watering, during dry and wet periods over 12 months. According to the results, the SAR was determined, and the water in the monitored wells was classified as having a high risk of salinization and a medium risk of sodium adsorption in the soil (C3 - S2), and as having a high risk of salinity and a low risk of sodification (C3 - S1). Therefore, its use for irrigation is recommended only with appropriate management and drainage, in addition to using salt-tolerant o crops, given the risk of soil salinization and crop toxicity. An improvement in SAR was observed in well 2, from the dry to the wet period, shifting from an extremely high risk of salinization and a very strong risk of sodium adsorption in the soil (C5 - S4) to an extremely high risk of salinization and a medium risk of sodium adsorption in the soil (C5 - S2), not being recommended for use of water for irrigation. By analyzing the EC, total dissolved solids, and sodium parameters, the water use classification for animal watering was conducted for poultry, cattle, goats, horses, and swine. Wells 2, 3, 4, and 5 presented the worst water quality indicator values due to the discharge of untreated sewage into the Sucurú river. However, there was an attenuation of these indicators from well 4 onward, due to the mixing of treated and untreated sewage and the filtration occurring along the alluvium, improving the water quality available for irrigation and animal watering. The recommended uses for irrigation and animal watering in the study area were classified, during the dry and rainy seasons.