Moon, and 32 co-authors reported in 2019 that they processed sediment to accurately characterize the spatially-resolved depth profiles of geophysical and geochemical properties along with signatures of microbial density and activity remains a challenge especially in complex contaminated environments. To provide site assessment for a larger study, the authors processed cores from two sediment boreholes from background and contaminated core sediments and surrounding groundwater from the ENIGMA Field Research Site at the United States Department of Energy (DOE) Oak Ridge Reservation (ORR).
The authors compared fresh core sediments by depth to capture the changes in sediment structure, sediment minerals, biomass, and pore water [aka groundwater] geochemistry [aka hydrochemistry] in terms of major and trace elements including contaminants, cations, anions, and organic acids. Soil pore-water [groundwater?] samples were matched (?) to groundwater level, flow rate, and preferential flows and compared to homogenized groundwater-only samples from neighboring monitoring wells. This environmental systems approach provided detailed site-specific biogeochemical information from the various properties of subsurface media to reveal the influences of solid, liquid, and gas phases.
Analysis of groundwater from nearby wells only revealed high sulfate and nitrate concentrations while the same analysis using sediment pore water samples with depth was able to suggest areas high in sulfate and nitrate- reducing bacteria based on their decreased concentration and production of reduced by-products that could not be seen [? aka observed] in the groundwater samples. Positive correlations among pore-water content, total organic carbon, trace metals and clay minerals revealed a more complicated relationship among contaminant, sediment texture, groundwater table, and biomass. This suggested that groundwater predominantly flowed through preferential paths with high flux and little mixing with water in the interstices of sediment particles, which could impact microbial activity [What? aka BS].
The abundant clay minerals with high surface area and high water-holding capacity of micro-pores of the fine clay rich layer suggest suppression of nutrient supply to microbes from the surface. The fluctuating capillary interface had high concentrations of Fe and Mn-oxides combined with trace elements including U, Th, Sr, Ba, Cu, and Co. This suggests the mobility of highly "toxic" [aka term used by anti-nuclear groups] elements, sediment structure, and biogeochemical factors are all linked together to impact microbial communities, emphasizing that solid interfaces play an important role in determining the abundance of bacteria in the sediments.
[Note the affiliations of the above authors...mostly engineers, biologists, etc. The paper reads like it as well. Too bad an actual professional hydrogeologist didn't have input to this project. Seems by the number of authors, everyone else did ...]
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