MICROBIAL COMMUNITY RESPONSES TO DRILLING INDUCED PERTURBATIONS IN A HARD ROCK AQUIFER

The Coast Range Ophiolite Microbial Observatory (CROMO) is a series of wells drilled into serpentinized soil and bedrock in Northern California, accessing high pH, moderately saline aquifers. The site consists of 4 wells drilled over 30 years ago, and 8 new wells drilled in August of 2011. Filtered, ozonated water was used to drill the new wells in 2011 to minimize subsurface contamination. Following drilling in 2011, the well network has been sampled 2-3 times per year for molecular biology and geochemistry. Recent analyses of this time series dataset has indicated that drilling activity caused a significant perturbance to subsurface geochemistry and the resident microorganisms. Geochemical data indicates that the water became more oxidizing and hypoxic and shows increased concentrations of dissolved hydrogen and acetate. Analyses of the microbial communities during this same time show an increase in microbial diversity, followed by a subsequent decrease, which occurs at the same time the geochemistry appears to begin re-stabilizing.

Preliminary analyses indicate that microbial communities in the aquifer responded to drilling activity and the resulting geochemical changes. Differential abundance and network analyses have shown that organisms from the candidate genus Serpentinomonas appear to have been significantly more abundant following drilling activity. Important sulfur and methane cycling microorganisms have been identified as being significantly more abundant in recovery time points. Time series geochemical data will be correlated with changes in the abundance of these key taxa in concert with data from metagenome assembled genomes to assess potential functional responses to drilling perturbation. In addition to this the role of rare taxa in the microbial community stress response will be assessed.

Results from this work will provide information on microbial community responses to drilling activity in hard rock aquifers and will also serve as a basis for better understanding the biogeochemistry of recently drilled sites. It will also contribute towards our growing understanding of how different types of groundwater perturbations affect endemic microbial communities and biogeochemical cycling.