Modelo de recarga e circulação da água subterrânea utilizando dados hidroquímicos e isotópicos de 18O, 2H e 3H em rochas cristalinas do sul do estado do Espírito Santo

Abstract

The groundwater demand in the state of Espírito Santo (Brazil), is growing up considerably due to the events of drought in recent years. However, the lack of hydrogeological knowledge compromises water-well location and the prediction of the quality of water, mainly where crystalline rocks occur. This work aimed to evaluate the hydrogeochemical characteristics of the Crystalline Aquifer System in the Itapemirim watershed (IRW), located in the Southern part of Espírito Santo, looking for the role that plays the conditioners and variables in the groundwater recharge and quality, also contributing to the understanding of its conceptual model of circulation. . In the High IRW portion where the highest altitudes and the most rugged terrain occur, groundwater is mixed and little mineralized (244.60 μS.cm-1), with elements provided by the weathering of igneous and metamorphic silicate rocks. In the Medium IRW portion, where temperatures are higher, lower altitudes and smoother relief, groundwater is predominantly sodic mixed or mixed chlorinated and progressively more mineralized (991.38 μS.cm-1), due to the contribution of rocks silicates in association with carbonate lithotypes and greater evaporation during recharge. The isotopic signature of rainwater is defined by the equation δ²H = 8.49δ 18O + 18.97, showing fractionation of air masses in a condition of non-physical-chemical balance. The isotopic signature of groundwater is similar to rainwater, indicating rapid recharge with variations according to climatic conditions, especially in the warmer areas where isotopic deviations of groundwater from some wells depart from the local meteorological line. The isotopic signature is close to rainwater and renewal times less than 25.75 years. Besides that, the isotopic signature is more enriched and the renewal times of up to 85 years. There is a trend towards greater mineralization, isotopic enrichment and renewal times, which gives groundwater circulation in topographically elevated regions towards the lower portions under the influence mainly of the relief. Land use and occupation have a punctual influence on water quality, especially in places close to industrial or agricultural activities. This work proposes a model that shows that the recharging of the crystalline aquifer system occurs in the entire study area, with the circulation governed by flow lines from local to regional scale.