Reactivity of pyrite and organic carbon as electron donors for biogeochemical processes in the fractured Jurassic Lincolnshire limestone aquifer, UK

In this study, the weathering profiles of limestone blocks in the Jurassic Lincolnshire limestone (UK) are used to determine the spatial variation in concentration of electron donors (organic carbon and pyrite) that might drive subsurface microbial respiration, including denitrification. Organic carbon concentrations were found to be constant throughout the block transects. In contrast, sulphur and pyrite–iron concentrations were significantly higher in the unweathered zones in comparison to the weathered zones. Moreover, acid-extractable iron concentrations were significantly higher in the weathered zones in comparison to those of the unweathered zones. This suggests that pyrite is operating as the main electron donor in this system and that organic carbon is unreactive. Therefore, potentially beneficial microbial processes such as denitrification of agrochemically-contaminated groundwater will be limited, not by availability of organic carbon, but by availability of pyrite.