The impacts of long-term groundwater pumping on subterranean microbial community structure in deep aquifer.

(1) Background: Accretionary prisms are mainly composed of ancient marine sediment scraped from the subducting oceanic plate at a convergent plate boundary. Deep aquifers associated with accretionary prisms contain large amounts of natural gas and groundwater, which can be sampled by using wells. However, there have been no studies on how groundwater pumping and natural gas sampling affect deep subsurface environments. (2) Methods: Stable isotopic analysis, Cultivation-dependent and -independent methods (e.g., Next generation sequencing and cloning sequencing based on 16S rRNA gene) were used to describe the prokaryotic community. (3) Results: Time variation of environmental data, every kind of ion concentrations, oxygen and hydrogen stable isotope ratios, and natural gas composition obtained from well were not observed and these data were almost constant. it was shown that long-term pumping has little effect on the environmental parameters of groundwater. However, DNA analysis showed dominant prokaryotic species changed from Thermoanaerobacteriales and Clostridiales to Archaeoglobales (sulfate-reducing archaea). Furthermore, archaeal growth temperature of each sampling date increased from 42°C to 55°C. These results indicate groundwater pumping promotes groundwater flow in deep aquifers and changes microbial community in groundwater to one with a growth temperature more similar to the in situ temperature.