Investigating groundwater–surface water interactions to understand hydrogeochemical processes in a carbonate mountain basin in Central Italy

Groundwater (GW) – surface water (SW) interactions regulate the hydrogeochemical processes of many rivers in the Italian central Apennine. Carbonate aquifers play a key role in sustaining the river discharge during no-recharge periods, ensuring the ecological flow, providing drinking water, and modulating solute exchanges related to physical-chemical weathering processes. The Apennine Mountain basins represent sentinels for studying the ongoing climate change in the Mediterranean area as they are scarcely anthropized. Qualiquantitative monitoring of river waters provides essential information for understanding hydrogeochemical processes that are often challenging to quantify. For instance, the river’s dissolved loads are a marker for studying the consumption of atmospheric CO2 by chemical weathering of carbonate minerals. The correlation between erosion and chemical weathering could play a key role in the global carbon cycle, especially in the steepest mountainous regions. To estimate the consumption of atmospheric CO2, a limestone mountain river basin mainly fed by GW is selected. Since 2017, several parameters have been continuously monitored, such as the discharges in some river sections, weather parameters, electrical conductivity and water river temperature, etc. A survey by a thermal drone during the no-recharge period allowed us to identify the river stretches fed by GW. In the same period, discharge measures by electromagnetic devices coupled with tracer tests and geochemical-isotopic river water data allowed the quantification of the GW component. Moreover, a self-implemented water budget model helped to better investigate river discharge response to rainy periods in which erosion and chemical weathering processes are significant. By an integrated approach, the work presents the preliminary results aiming to understand the relationship between dissolved load (e.g., alkalinity, electrical conductivity, etc.) and the discharge in a river where GW prevails.