Assessing the seasonal variability of shallow underground waters quality from a volcanic – sedimentary formation during El Niño event in Panama

Abstract Providing drinking water to growing populations has become a worldwide concern. Therefore, in many countries some groundwater reserves are now being used to supply drinking water in remote urban areas. The state of these groundwater reserves is strongly influenced by the local geological conditions. Furthermore, climate change has caused a decrease in the periodicity of environmental conditions such as rainfalls, a key driver in replenishing these reserves. In 2019, the weak El Niño event affected the rainfall pattern, as well as physical and chemical quality of shallow ground waters in Panama. Within this study, the northwestern central region of Panama groundwaters have been systematically characterized during El Niño 2018 – 2019 event. Our results indicate that changes in values of physicochemical parameters such as alkalinity, pH and conductivity are related to changes in the amount of rainfall reported in the region starting from dry season (DS) to the rainy season (RS). Chloride was recorded as an indicator of anthropogenic activity and/or the effect of human populations on specific sites in the aquifer recharge zones. Lead (Pb2+), Zinc (Zn2+), Manganese (Mn2+), and Copper (Cu2+) concentrations in the groundwater were evaluated during the DS and RS 2019. Recorded data indicates sub – lethal concentrations of Pb2+, Zn2+, Mn2+ were associated to changes in alkalinity values of groundwater during the DS. While during the RS, a decrease in pH values favored the dissolution of Cu2+ and Zn2+. Our findings suggest that seasonal rainfall deficits modify shallow underground water alkalinity and pH values, inducing the redissolution of Pb2+, Zn2+, Mn2+, Cu 2+and exposing populations to sub – lethal concentrations of those microelements.