Hydrogeochemical characterization and indicators of anthropogenic influence in groundwater around Guanabara Bay, Rio de Janeiro, Brazil

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The global demand for water sources for human consumption has been increasing over the last century. The degradation of water bodies and aquifers has made the planning and management of these natural resources crucial. In this context, this study focuses on the hydrogeochemical characterization of aquifers surrounding the of Guanabara Bay Hydrographic Region (GBHR), located in Rio de Janeiro, which stands out as an area with a high population density associated with elevated levels of environmental degradation. A total of 228 wells were analyzed, separated by aquifer types, resulting in 138 fissured and 90 porous aquifers, predominantly sodium-rich groundwaters. This predominance this hydrochemical facies can be attributed to the influence of the saline influence, given the proximity to the ocean, and anthropogenic activities, such as the discharge of industrial and urban effluents, which alter the chemical composition of groundwater. From the mixing diagram, it was found that most of the sampled wells are in the field of silicate rocks for both types of aquifers. In porous aquifers, a significant number of wells under greater influence of effluents/evaporites were observed in the eastern portion of GBHR, whereas in fissured aquifers, effluents/evaporites are predominantly concentrated in the western portion of the study area. The high variability of the Inorganic Chemical Index may indicate zones of point or diffuse pollution, influenced by effluent discharges, surface runoff, and contaminant infiltration. This variation reveals a distinctive pattern related to land use and aquifer type in the studied region when observed spatially. The use of a multivariate statistical technique (factor analysis) corroborates the influence of natural processes, like weathering and seawater intrusion in wells close to the coast and the anthropogenic processes, such as domestic/agricultural/industrial effluents influence in wells far from the coast. This study highlights the importance of understanding the hydrogeochemistry of aquifers in urban and industrial areas, not only for the preservation of the local ecosystem but also for public health and sustainable development. The results point to the need for integrated water resource management policies that consider both environmental conservation and economic development, thus ensuring a balance between the use and protection of groundwater around Guanabara Bay.