Abstract
Abstract The 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 Sao Francisco River. The results were plotted in a dD ‰ versus δ18O ‰ 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 dD and δ18O 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 87Sr/86Sr ratio and isotopic groundwater dating assist in the interpretations.
Highlights
Petrolina County is located in the southwestern part of Pernambuco State in the Northeastern region of Brazil (Figure 1)
The sample CAN-08 is located next to the São Francisco River and as the numbering of the samples decreases as they get close to the Uruás Village
The twenty four groundwater samples collected in wells have been plotted on the δ18O versus δD graph along with the global and local meteoric water line
Summary
Petrolina County is located in the southwestern part of Pernambuco State in the Northeastern region of Brazil (Figure 1). Together with Juazeiro County, it forms one of the most promising irrigation poles in the São Francisco River watershed. The region is located between the boundary of the São Francisco Craton and the Borborema Province which is represented by the Riacho do Pontal Mobile Belt. In the southern region of the county, there are outcrops of the Gavião Block rocks mainly gneiss. The rocks of the Riacho do Pontal Mobile Belt are exposed and represented mainly by schist and marble. The rocks are dated from the Archean to the Neoproterozoic Eras.
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