Piezometric Behavior in the Amazonian Lateritic Plateaus: Implications of Climate Changes to the Recharge of the Alter do Chão Aquifer System

Abstract

Potentiometric and pluviometric datasets were evaluated to understand the behavior of aquifer recharge in the bauxite plateaus in the Porto Trombetas region, Pará, Northern Brazil. The datasets are originated from three monitoring wells and an automatic climatological station. The local groundwater is related to the Alter do Chao Aquifer System, which despite being unconfined in valley regions, is semiconfined in the plateaus areas. The aquifer recharge occurs by direct infiltration and by leakage from the aquitard in the unconfined and semiconfined portions, respectively. Precipitation declined by 27% between 2002 and 2017. The rains accumulated between February and April are the most important for the recharge processes since this period is marked by higher absolute precipitation (up to 300 mm/month) and less deviation from the historical pattern. The recharge measured by the annual fluctuation of the water table also declined significantly in the 2010-2016 period. Statistical analysis demonstrates that in the case of a permanent climate change, expressed by rainfall reducing, the aquifer recharge would diminish at a non-linear rate, which is also expected for the base flow rates. In addition, data evaluation reveals that deforestation intensely decreases the recharge rates, as observed in the Aviso Plateau mining site. The results demonstrate that the water table fluctuations must be considered when modeling Global Climate Changes since the maintenance of surface flow rates (springs, lakes and streams) depends on aquifers baseflow. The result of the statistical analysis can be also applied to regions where climate patterns are strong seasonal, as the Savannah of Central Brazil.