Seasonal variation in groundwater quality across different hydrogeological domains in the Piauí River basin (Sergipe)

Abstract

This study evaluated groundwater quality in the Piauí River Basin (Sergipe, Brazil) with emphasis on potability for human supply, considering seasonal variation and the karst, fractured, and granular hydrogeological domains. Fifteen wells were sampled in the dry and rainy seasons of 2022. Chloride, nitrate, sulfate, sodium, total dissolved solids (TDS), and hardness were analyzed and compared with the limits set by CONAMA Resolution 396/2008 and Brazilian Ministry of Health Ordinance GM/MS No. 888/2021. Results showed clear seasonal effects and a direct lithologic control on water composition. During the rainy season, chloride, TDS, nitrate, sulfate, and sodium exceeded legal limits in wells within the karst domain, consistent with carbonate-rock dissolution. In the dry season, elevated nitrate occurred mainly in the fractured and granular domains. Hardness exceeded the sanitary limit in the karst domain during the rainy period, whereas in the fractured domain high nitrate coincided with higher hardness, likely linked to the leaching of agricultural fertilizers. The hydrogeological domain was decisive: the karst domain showed higher sodium, chloride, and sulfate, while the fractured domain was dominated by nitrate. Agricultural activity and the lack of basic sanitation were identified as potential contamination sources. The study highlights the need for continuous monitoring and sustainable management strategies to protect aquifers and addresses a gap on the comparative influence of hydrogeological domains in semiarid regions, improving understanding of groundwater vulnerability and informing preservation-oriented public policies.