Plant-mediated coupling between karst hydrogeology and element dynamics in groundwater dependent ecosystems

Imbalances between fluxes entering and exiting ecosystem components induce complex ecological dynamics and differential allocations of matter - a process exemplified by plants with their accumulation capabilities, affecting the dynamics of elements and their redistribution across trophic levels. At the interface between different ecosystems, such as underground and groundwater dependent ecosystems (GDEs), their role as integrators and reservoirs of elements may affect system coupling, with the emergence of unique behaviours. Through the study of 19 nutrients and non-essential elements in water, sediments and plants of two pristine freshwater ecosystems of the Cilento and Vallo di Diano (southern Italy), we shed light on the unique interaction between complex karst systems and their GDEs. Indeed, karst flushing and piston-flow effects induce the release of short pulses of water with high concentrations of several elements, especially Cd, Cr, Ni and Zn. Pulses are undetectable in water and do not induce variations in total and bioavailable concentrations in sediments, but elements are accumulated by plants resulting in concentrations several-fold higher than in heavily contaminated rivers. Transient changes in element concentrations can thus affect, through element transfer in trophic webs, GDEs ecological dynamics at longer temporal and spatial scales.