Impacts of climate change on fragile alkaline lakes: New hydrogeochemical and hydrogeological insights from Bagno dell’Acqua (Pantelleria Island, Italy)

Study region: Alkaline lakes are among the most extreme aquatic environments on Earth, offering insights into unique ecosystems that may be similar to those that gave rise to life on Earth and potentially other planets like Mars. Despite their hydrogeological and geochemical significance, the temporal and spatial evolution of alkaline lakes remains poorly understood due to limited long-term data. To address this, we monitored the volcanic alkaline lake Bagno dell’Acqua (Pantelleria Island, Southern Italy) and nearby springs and wells from May 2021 to June 2023. Study focus: Three sampling campaigns were conducted at ten sites. Chemical data confirm a connection between the lake and surrounding thermal springs, with clear evidence of calcium and strontium removal via mineral precipitation. Isotopic analyses (δ¹⁸O, δ²H-H₂O; δ³⁴S, δ¹⁸O-SO₄; ⁸⁷Sr/⁸⁶Sr; δ¹¹B) and gas compositions further elucidate the system’s geochemical dynamics. New hydrological insights for the region: Over the past two decades, the lake’s hydrogeological water budget shows reduced recharge and increased evaporation compared to the 1990s, resulting in a net water loss of 49%. Geochemical markers indicate rising solute concentrations, consistent with reduced freshwater inflow and intensified evaporation. If current trends persist, a progressive increase in salinity and consequently eutrophication may occur, with possible implications for the lake’s biogeochemical functioning that warrant further investigation. This study provides a valuable dataset for the conservation and management of closed-basin alkaline lakes and highlights the importance of long-term monitoring under changing climatic conditions.