Relationships of stable isotopes, water-rock interaction and salinization in fractured aquifers, Petrolina region, Pernambuco State, Brazil

Abstract

Relationships of stable isotopes, water-rock interaction and salinization in fractured aquifers, Petrolina region, Pernambuco State, Brazil AbstractThe Petrolina County, Pernambuco State, Brazil, presents specificities that make it unique from a hydrogeological point of view. Water resource scarcity is both a quantitative and qualitative issue. The climate is classified as semiarid, having low precipitation, along with high temperatures and evapotranspiration rates. Aquifer zones are related to low connected fractures resulting in a restricted water flow in the aquifer. The recharge is limited and the groundwater salinity is high. Stable isotope analyses of H and O were developed in groundwater samples (with different electrical conductivity) and surface water collected in a bypass channel flowing from the São Francisco River. The results were plotted in a δD ‰ versus δ 18 O ‰ graph along with the curves of the global and local meteoric water line. Groundwater samples showed unexpected results showing a lighter sign pattern when compared to the meteoric waters. More negative δD and δ 18 O values indicate an enrichment in light isotopes, which show that this process is not influenced by surface processes, where the enrichment occurs in heavy isotopes due to evaporation. The isotopic signature observed is interpreted either as resulting from the water-rock interaction, or as resulting from recharge from paleo rains. The waters are old and show restricted flow. So the water-rock contact time is extended. In the rock weathering processes, through the hydration of feldspars, there is preferential assimilation of heavy isotopes at the expense of the lighter ones that remain in the water. Analyses of the 87 Sr/ 86 Sr ratio and isotopic groundwater dating assist in the interpretations.

Avaliação de processos naturais de salinização de águas subterrâneas na porção leste da bacia do rio Cachoeira, Bahia

“…A salinidade da água é um parâmetro mensurável pela concentração de sólidos totais dissolvidos (STD). Entretanto, em muitas situações, apenas medidas de condutividade elétrica (CE) são realizadas para avaliar a salinização de águas subterrâneas (ex: MONTENEGRO et al 2003, ANDRADE et al 2012, SILVA et al 2018. A proposição do modelo empírico relacionando o STD ao CE (Equação 6), permite que as medidas de CE forneçam valores equivalentes de STD, permitindo estimativas mais precisas da salinidade da água subterrânea no semiárido brasileiro.…”

“…As condições climáticas observadas no semiárido propiciam a salinização das águas subterrâneas. Embora a salinização de águas subterrâneas no semiárido do nordeste brasileiro seja muito reportada na literatura (MOREIRA-NORDEMANN 1984, ANDRADE et al 1999, BOUAZIZ et al 2011, ALMEIDA & FRISCHKORN 2015, SILVA et al 2018, estudos sobre a avaliação quantitativa dos processos que governam este fenômeno são escassos.…”