Rivers receive an enormous variety of chemical and biological inputs from watersheds, including organic matter, regional geochemical erosion, agricultural runoff and municipal wastewater. In addition, the soil microbiome, which has incredible functional diversity, is continuously transported into rivers. However, the relationship between microbial functional diversity in riverine sediment relative to soils in the same watershed has received little attention. The Kanawha-New River Basin (WV) encompasses 12,000 square miles of Appalachian Mountains. The watershed is primarily forested but includes large sections of surface mining and considerable riverside industrial development. Yearly river flow varies widely with high discharge events exceeding 100,000 cubic ft per second. Our long-term research seeks to understand the impact of land-use practices on riverine microbial biogeochemical cycles and bioremediation processes. For this study, we sampled microbiome diversity in river sediment and nearby upland forest in order to understand the drivers of functional diversity in the highly mobile upper sediment layer. We sampled the sediment microbiome from five widely-spaced locations along an 80 km section of the Kanawha River as well as an upland forest soil in the watershed. Replicate sediment samples were collected from 0-5 and 5-10 cm layers of sediment using an 8 cm diameter corer. Total DNA was extracted with the PowerMax soil kit and 70 gigabases of sequence were obtained with Illumina HiSeq. Metal concentrations were measured with ICP-OES. Common freshwater ions were measured with Dionex ion chromatography. Organic carbon was measured with an Aurora Total Organic Carbon Analyzer. Metagenome analysis was done with MG-RAST and the STAMP statistical package.
Results/Conclusions
Profiles of river sediment chemistry using ordination and hierarchical clustering showed that each location was distinct, particularly with regard to organic carbon, nitrogen and sulfur compounds, copper and zinc. SEED subsystem categories of functions were used to compare functional gene abundance in ten river sediment metagenomes to three upland forest soil metagenomes in terms of biogeochemical processes. Using a Multiple Group Test (Storey’s FDR corrected, q <0.05), the sediment microbiome was distinct from forest soil in terms of nitrogen, sulfur and carbohydrate metabolism, and respiration pathways, for all SEED subsystem levels (1-4). Among the functions enriched in the sediment were methanogenesis, iron transport and transposable elements. Conclusion: The microbiome of the mobile upper sediment layer was distinct from nearby forest soil in the watershed, particularly for anaerobic metabolism, in spite of frequent mixing due to disruptive river discharge events. Acknowledgements: NSF grant #OIA-1458952.