Effects of the 2021 La Palma volcanic eruption on groundwater resources (part II): Hydrochemical impacts

Volcanic eruptions can have significant implications for the management and sustainability of water resources in volcanic islands. The recent 2021 eruption of the Tajogaite volcano in La Palma Island (Canary Islands, Spain) raised concerns regarding its potential impact on groundwater resources. This study is the second part of a series investigating the hydrogeochemical impacts of the eruption. The study involved conducting three groundwater sampling campaigns during the eruption and two after the eruption, six months and one year after the eruption ceased. A total of 15 monitored points, including piezometers, wells, water galleries, and main gully collector of the island, all relatively close (2-15 km) to the erupted volcano, were sampled for the analysis of major, minor, and trace elements, physiochemical parameters, which were measured on-site. Statistical analyses were performed to assess the differences in groundwater composition before, during, and after the eruption. To evaluate the differences in water quality compared to pre-eruption events, 33 additional historical groundwater samples provided by the local Water Authority were assessed, and 103 groundwater analysis results from the groundwater data base of the Spanish National Geological Survey (IGME) were considered. The results of the study showed low but statistically significant changes in pH, T, conductivity and groundwater composition, mainly related to the high increases in several trace element concentrations, such as Al, Cr, Fe, Mo, Ni, Sr, Th, Tl, V, Zn, Ba, Cd, Co, Cu, Pb and U, with increments in various orders of magnitude for several elements. This increase was found to be highly influenced by the sample distance to the volcano during the eruption stage. The significance of these findings lies in their usefulness to enhance our understanding of the effects of volcanic eruptions on groundwater quality resources and demonstrate their resilience to this hazardous phenomenon, which ultimately underscores their reliability.