B21B-0039:
Redox Fluctuation Influences Viral Abundance in the Reduced Zone of a Shallow Alluvial Aquifer in Rifle, CO
Tuesday, 16 December 2014
Donald Pan1, Kenneth Hurst Williams2, Mark Robbins2 and Karrie A Weber1, (1)University of Nebraska Lincoln, Lincoln, NE, United States, (2)Lawrence Berkeley National Laboratory, Berkeley, CA, United States
Abstract:
Naturally reduced zones (NRZs) within alluvial aquifers contain naturally elevated concentrations of organic carbon (OC) and can play a role in controlling the fate of redox-active contaminants. OC in NRZs stimulates microbial activity through coupling of OC oxidation to reduction of subsurface electron acceptors. Stimulation of the indigenous microbial community also results in the stimulation of the viral community. Viruses are the most abundant biological entity on Earth and can indirectly influence carbon cycling by infecting and lysing host cells, resulting in release of OC bound in biomass. In the alluvial aquifer near Rifle, CO, prior acetate injection resulted in reductive immobilization of U and a reduced zone simulating a NRZ, with elevated ferrous iron and sulfide (53.2–62.5 µM and 0.2–3.1 µM, respectively). To study the effects of redox fluctuations in a RZ, oxygenated groundwater was injected. Prior to injection, groundwater was suboxic (0.05–0.11 mg/L). Amended O2 was immediately consumed in the RZ. While cell numbers didn’t significantly increase, viruses increased from 1.1x106–2.1x106 mL-1 to 2.3x106–4.6x106 mL-1. VCR increased 1.8–3.4 fold from 3.9–10.1 to 11.0–17.9, demonstrating microbial activity. These changes were associated with large fluctuations of groundwater dissolved OC, suggesting viral release of OC from cellular biomass. Groundwater ORP decreased from an initial -146 mV – -132 mV to -317 mV – -304 mV, indicating an increase in the supply of available electron donors. Thus, rather than expected oxidative solubilization of U following amendment of O2, soluble U decreased, suggesting likely U reduction in the RZ. Fe and S fluctuated, but changes were not associated with aqueous U. Across the whole floodplain, viral abundance is correlated to groundwater dissolved OC, suggesting that viruses may be contributing to the liberalization of dissolved OC from biomass in NRZs, allowing turnover of carbon and reduction of contaminants of interest, independent of external acetate amendment. This is especially important considering the role of OC in controlling the fate and transport of contaminants in aquifers. These results suggest that viruses are an important factor to consider in the turnover and retention of carbon in the subsurface.
