| Groundwater is a significant reservoir for freshwater and carbon, especially in semi-arid
regions. With the changing climate, interpreting recharge characteristics, geochemical evolution,
architecture of subsurface flow, and residence times is essential to assess the vulnerability of
aquifers. In this study, we collected groundwater samples along a longitudinal and elevational
transect as well as potential source signatures from springs, an irrigation pond, and precipitation.
All samples were analyzed for a range of geochemical and age tracers. We found that springs
emerged from shallow, undersaturated aquifers undergoing calcite dissolution in open-system
conditions. Shallow aquifers, including springs, were recharged by modern waters indicating
vulnerability to anthropogenic influence and the changing climate. Deeper aquifers developed in
basaltic environments, reaching calcite saturation under closed-system conditions, and were
recharged by paleowaters. Due to longer residence times, deeper aquifers become carbon sinks
and therefore, unsustainable for use. In summation, the movement of water and carbon through
the subsurface is spatially and temporally variable as geochemical evolution and residence time
increase with aquifer depth. |