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Salinity Effects on Nitrogen Dynamics in Shallow, Coastal Sediments

ABSTRACT<br/>OCE- 0350651<br/><br/>In this study, researchers at the University of Texas at Austin hope to advance our understanding of the mechanisms controlling the concentrations, forms, transformation rates, and fate of biologically relevant nitrogen compounds over a range of salinities in coastal ecosystems. Nitrogen often limits primary production in coastal regions. Shallow water sediments are primary biogeochemical sites regulating the transformation and fate of N in coastal ecosystems. Upper sediment layers provide environments conducive to microbial N cycle transformations, including organic N mineralization, nitrification (to nitrite and nitrate), denitrification, and dissimilatory nitrate reduction to ammonium (DNRA), but the importance of each process varies with salinity and other factors. Recent evidence indicates that traditional paradigms of key processes, such as denitrification, may not be accurate or complete for all sediment systems. The objectives of this investigation are to compare and combine chemical, isotopic, and molecular biology methods to define N transformation mechanisms in coastal systems over a salinity gradient. Specific hypotheses to be examined are:<br/><br/>1. Salinity and available organic matter control the fate of regenerated N by affecting sulfide concentrations in shallow coastal ecosystems.<br/>2. The importance of N2O release and DNRA, relative to N2 production, increases with salinity in reduced sediments.<br/><br/>The experiments are expected to yield information relevant to issues of international concern including coastal eutrophication, harmful algal blooms, freshwater supply, and global change. They will advance marine methodological development by combining molecular biology techniques with chemical and stable isotopic approaches to clarify the structure and function of bacteria involved in N transformations. Opportunities will be provided for minority institution students and high school teachers and students to participate in field research on coastal environments and learn about the importance of nutrients and salinity to coastal ecosystem processes.

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