Abstract
Physical properties of sediments are commonly used to define subsurface lithofacies and these same physical properties influence subsurface microbial communities. This suggests an (unexploited) opportunity to use the spatial distribution of facies to predict spatial variation in biogeochemically relevant microbial attributes. Here, we characterize three biogeochemical facies—oxidized, reduced, and transition—within one lithofacies and elucidate relationships among facies features and microbial community biomass, richness, and composition. Consistent with previous observations of biogeochemical hotspots at environmental transition zones, we find elevated biomass within a biogeochemical facies that occurred at the transition between oxidized and reduced biogeochemical facies. Microbial richness—the number of microbial taxa—was lower within the reduced facies and was well-explained by a combination of pH and mineralogy. Null modeling revealed that microbial community composition was influenced by ecological selection imposed by redox state and mineralogy, possibly due to effects on nutrient availability or transport. As an illustrative case, we predict microbial biomass concentration across a three-dimensional spatial domain by coupling the spatial distribution of subsurface biogeochemical facies with biomass-facies relationships revealed here. We expect that merging such an approach with hydro-biogeochemical models will provide important constraints on simulated dynamics, thereby reducing uncertainty in model predictions.
Highlights
Subsurface environments are heterogeneous three-dimensional systems characterized by variation in redox state, mineralogy, and physical structure
We evaluate the hypothesis that microbial community composition will be most strongly related to redox state—as a proxy for dominant biogeochemical processes—and that variation in sediment mineralogy, organic carbon content, and/or pH4,5,6,25,26,27,28 will have additional influences, but of a lesser impact
Sediment samples examined here originated below the geologic unconformity that forms the interface between the top of the Ringold mud lithofacies and the base of the Hanford Formation
Summary
Subsurface environments are heterogeneous three-dimensional systems characterized by variation in redox state, mineralogy, and physical structure. The temporal stability of facies allows characterization of their spatial distributions, and this has been leveraged in hydro-biogeochemical models[13,14,15]. This suggests that facies-microbe relationships could be coupled with facies spatial distributions to generate spatial predictions of microbial community properties. While many studies have directly or indirectly investigated microbial communities and their metabolic processes across facies[17,18,19,20], the resulting microbe-facies relationships have not been leveraged to generate spatial predictions of subsurface microbial communities. Fluvio-lacustrine Framboid Lithofacies β-mean nearest taxon distance (βMNTD) β-nearest taxon index (βNTI) Nonmetric multidimensional scaling (NMDS)
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