Geochemical characteristics control potential microbial activity in exposed Late Quaternary alluvial deposits

Abstract

Different stratigraphic sequences of Late Quaternary sediments present in a vertically exposed 29 m deep river cliff were used as a model system to understand geochemical relationships with potential microbial activity in semiarid alluvial sediments. Microbial activities involved in carbon (C) and phosphorus (P) cycling were measured by dehydrogenase, alkaline phosphatase, and microbial respiration activities. We did not observe patterns in microbial activities that could be explained by sample depth. An extensive analysis of the physical and geochemical characteristics of exposed sediments was conducted along with multivariate statistical analysis to determine the influence of geochemical variables on potential microbial activity. Principal component analysis (PCA) and canonical correlation analysis (CCA) together with Pearson correlation analysis indicated that sediment organic carbon, moisture content, palynofacies components (acid-resistant particulate organic matter) such as fungal spores, brown carbon, structured carbon, and concentrations of Al2O3, FeO, MgO, MnO, and Zr were associated significantly with microbial activities in river cliff sediment deposits. These findings highlight drivers of microbial activity with consequences for C and P biogeochemical cycles in semiarid alluvial soils/sediments of river floodplains.