What Microbial Signature Means in Terms of Groundwater Dynamics, Vulnerability and Residence Time-Comparison of Shallow and Deep Karst Resources

The microbial signature is a fundamental characteristic of karst groundwater resources, both with respect to the natural state and potential pollution. Karst springs are regularly affected by water quality derogation in the course of recharge events. Deeper resources with longer groundwater residence times, on the other hand, may be free of fecal pollution and turbidity problems, what puts them into the focus for future exploration strategies. Both aquifer types are however still few understood regarding their microbiological constitution. Novel flow-cytometry data (TCC, Live/Dead cells and LNA/HNA cells) were assessed at shallow and deep resources of a karst system in the Swiss Jura Mountains. While spring results followed hydrological variations, the well data evidenced microbial stability, linked to the increased flow time of several years, and approaching equilibrium with the natural biocenosis of the groundwater ecosystem. Spring and well monitoring considers the end-members of karst groundwater dynamics and vulnerability. This allowed for (i) assessing the hydrogeological meaning of the flow-cytometry parameters, (ii) deducing general conclusions from the signature regarding karst functioning, and (iii) gaining deeper insight into microbial transport and fate processes. The findings provide a conceptual framework for the evolution of diverse microbiological parameters with residence time, contributing to the protection and management of karst resources.