Preliminary assessment of the relationships between rainfall, flow discharge and biodiversity changes in a karst spring system in central Italy

Groundwater-fed springs are relatively stable freshwater environments which harbor a valuable biodiversity and represent a precious water source for human needs. However, with ongoing global warming and increasing human footprint on natural systems, spring ecosystems are more and more exposed to hydrologic and physico-chemical alterations, which would in turn threaten their biodiversity. Recently, scientists claimed that an integrated “ecohydrogeological” approach, analyzing patterns and drivers of changes in spring environments from various perspectives, would greatly help in assuring the long-term preservation of these precious ecosystems. Following this plea, we studied both the ecological and the hydrological dynamics of the Presciano karst spring system (Abruzzo, Central Italy). The Crustacea Copepoda were chosen as target invertebrate group, since they are main components of the freshwater meiofauna and occur in all the groundwater-dependent ecosystems, groundwater-fed springs included. Specifically, we analyzed temporal changes in both copepod species richness and between-site differences in assemblage composition (i.e., beta diversity). The observed patterns were also contrasted to variations in measured physico-chemical parameters. On the hydrologic side, starting from rain gauge data, we implemented the CETEMPS Hydrological Model (CHyM) to derive a rain field with hourly resolution across the Gran Sasso – Sirente hydrogeological basin, which hosts the recharge areas feeding the Presciano spring. The modelled monthly cumulative rain, averaged across the Gran Sasso – Sirente basin, was then compared to the maximum and minimum monthly flow discharge values extracted from a hydrometric station located downstream the Presciano spring outlet. Finally, future rainfall simulations for the 2081-2091 decade were performed on the same area by forcing the CHyM software under the RCP8.5 emission trajectory, based on three different Regional Climate Models. Both species richness and beta diversity of the Presciano spring noticeably varied over time but variability of hydrochemistry could not comprehensively explain such changes, except for species turnover which was tightly related to between-site variability in water oxygenation. Seasonal discharge variations may thus have a more prominent role than local water conditions in determining the overall structure of spring meiofauna assemblages. Moreover, a not-negligible signal emerged from the comparison of precipitation and discharge temporal dynamics, indicating that accurately modelling rainfall in recharge areas would permit to better estimate and possibly forecast temporal variation in spring discharge. The future projections highlighted an overall predicted drop in precipitation across the Gran Sasso − Sirente basin, warning about possible groundwater lowering in karst springs in the next future.