Linking Organic Matter Composition to Shifting Baselines in the Coastal Sedimentary Nitrogen Cycle 

Global change models predict acceleration of the hydrologic cycle that results in increased organic matter and nitrogen loadings from continents into coastal and estuarine waters also subject to salinity intrusion from rising sea level.  How the coastal N-cycle responds to these pulsed scenarios has implications for coastal ocean productivity, resilience to eutrophication intensification, and export of N and carbon offshore.  This project considers direct reaction-scale controls on N biogeochemistry and indirect regulation of N reactions via other respiratory pathways through competition, stimulation and/or inhibition.  We examine the mechanisms controlling the balance between reactions that retain /deliver dissolved inorganic nitrogen (DIN) in sediments (mineralization, nitrification, dissimilatory nitrate reduction to ammonium-DNRA, N-fixation) and those that remove N from sediments (denitrification and anammox).  The multidisciplinary approach targets the role of OM source/chemical character on N cycling rates, N cycling gene expressions, and linkages to other respiratory pathways (e.g. sulfate reduction) through a series of laboratory and mesocosm experiments using geochemical, microbial, stable isotopic, and modeling techniques.