Ecology of wood in the Upper Mississippi River

Abstract

Wood is recognized as a key habitat structure in riverine ecosystems, yet we know relatively little about its role in large floodplain rivers such as the Upper Mississippi River. Despite its clear ecological importance, wood has actively been removed from large rivers for navigational and recreational purposes. Defining the ecological role of wood in large floodplain rivers, such as the Upper Mississippi River, is an important step towards developing better conservation, restoration, and management practices. Two differing yet interconnected objectives were examined. We surveyed shoreline wood in Pool 8 of the Upper Mississippi River quantify the subsidy and to gather insight into the mobility of wood within the pool. Evidence of wood movement in the main channel was clear, yet such evidence was less apparent in the smaller side channels. Riparian land cover was a significant factor in the accumulation of shoreline wood. Additionally, wood colonizing biofilms were sampled experimentally and from natural wood surfaces to understand how wood may directly support microbial communities. Greater biofilm biomass on wood surfaces, in comparison to inorganic surfaces, was found through in situ experimental deployments. Isotope analyses suggested direct assimilation of 𝛿𝛿15N & 𝛿𝛿13C from natural wood surfaces into their colonizing biofilms. Developing both our understanding of the availability of wood and the utilization of this resource by biofilms provides context to the importance of an allochthonous resource in the UMR.