BIOGEOCHEMICAL AND STABLE ISOTOPIC CONTROLS ON THE EVOLUTION OF CARBON AND SULFUR FROM THE CONFINED ZONE OF THE EDWARDS AQUIFER, TEXAS, USA

The relationship between microbial activity and carbon and sulfur cycling is being targeted for environmental remediation and water quality assessment. In this research, we aim to investigate the cycling of carbon and sulfur in surficial environments from aqueous fluids emanating from deep saline formations. We used geochemical, stable isotope, and membrane lipid analyses to investigate the geochemical changes and microbial community structure associated with carbon and sulfur cycling in surface and shallow environments. The study area focused on the artesian springs discharging the down-dip section of the karstic Edwards Aquifer in south central Texas, USA, having distinct freshwater and brackish water quality in the vicinity of its updip-downdip interface. We monitored the chemical and isotopic parameters over a 700-m stretch on a stream-pond system. The results showed a decrease in the alkalinity concentrations over distance with enrichment in carbon isotopic signatures (δ¹³C). The sulfate concentration decreased over distance with a slight enrichment in sulfur isotope (δ³⁴S) for the first 20 m and then a slight decrease in δ³⁴S values throughout. Microbial metabolism and it adaption to physiological stresses would results C and S cycling. A better understanding and utilization of these micro-biogeochemical processes will help open up the possibility of improving biocide performance in aquifer settings. A three-tier evolution process associated with the interaction of a deep saline fluid with a fresh-ponded water was observed, namely: A deep fluid control zone; a mixing zone, and a fresh-ponded water-controlled zone.