Bacterial migration through low-permeability fault zones in compartmentalised aquifer systems: a case study in Southern Italy

The aim of this study was to experimentally verify the significance of microbial transport through low-permeability fault zones in a compartmentalized carbonate aquifer system in Southern Italy. The temporal variability of microbial communities in two springs fed by the same aquifer system, but discharging up-and down-gradient of two low-permeability fault zones, was analyzed using a 16S rDNA polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE)-based approach. At both springs, a remarkable temporal variation in PCR-DGGE profiles was detected throughout the observation period. When comparing the PCR-DGGE profiles of the two springs, a synchronous evolution over time was observed. Moreover, the percent of PCR-DGGE bands common to both springs progressively increased from early (23%) to late recharge (70%), only to decrease once more in late recession (33%). Considering the hydrogeological and isotopic investigations and EC measurements, the results of biomolecular analyses demonstrate that, at the study site, compartments straddling the analyzed fault zones have microbial interconnections, despite the existence of low-permeability fault cores.