DISSERTATION RESEARCH: Importance of Novel Microbial Pathways of Nitrate Uptake by Freshwater Sediments

论文研究：淡水沉积物吸收硝酸盐的新微生物途径的重要性淡水中氮（N）水平的增加会威胁水质。 湿地和溪流中氮的去除在农业景观中特别重要，因为氮的出口与沿海沃茨中的低氧区和有害藻华有关。 研究表明，大部分人为增加到流域的氮（例如，作为肥料）在到达海洋之前通过水文系统的地下和地表沃茨的运输过程中损失。 硝态氮是氮素在水文系统中迁移的最主要形态。 到目前为止，大多数硝酸盐的去除已被归因于一种称为呼吸反硝化的细菌过程，这种去除大部分被怀疑发生在小溪流和湿地。 然而，最近的研究强调了其他细菌过程，可能是重要的，在去除硝酸盐从淡水系统中，包括异化硝酸盐还原铵（DNRA），硫化物氧化耦合反硝化作用，并通过铁非生物转化为DON。 本研究的目的是评估这些替代途径的硝酸盐去除在淡水生态系统中的普遍性和重要性。 最普遍的假设是，不同的淡水系统将在替代过程的相对重要性不同，这些差异将主要来自系统的地球化学和水文环境。 在各种淡水生态系统中，将利用景观调查和稳定同位素技术对清除途径进行量化。 研究结果将对生态系统的管理产生影响，以促进硝酸盐的去除。

DISSERTATION RESEARCH: Importance of novel microbial pathways of nitrate uptake by freshwater sedimentsIncreasing levels of nitrogen (N) in freshwaters can threaten water quality. The removal of N by wetlands and streams is of particular interest in agricultural landscapes because N export has been implicated in creating low-oxygen zones and harmful algal blooms in coastal waters. Studies indicate that most of the anthropogenic N added to watersheds (e.g., as fertilizer) is lost in transit through the ground and surface waters of the hydrologic system before reaching the oceans. Nitrate is the most important N form moving through hydrologic systems. To date, the majority of nitrate removal has been attributed to a bacterial process called respiratory denitrification, and much of this removal is suspected to occur in small streams and wetlands. However, recent research has highlighted other bacterial processes that may be important in removing nitrate from freshwater systems, including dissimilatory nitrate reduction to ammonium (DNRA), sulfide oxidation coupled to denitrification, and abiotic conversion to DON via iron. The goal of this research is to assess the prevalence and importance of these alternative pathways of nitrate removal in freshwater ecosystems. The most general hypothesis is that various freshwater systems will differ in the relative importance of alternative processes, and that these differences will arise primarily from the system's biogeochemical and hydrological setting. The removal pathways will be quantified using landscape survey and stable isotope techniques in a variety of freshwater ecosystems. The results will have implications for the management of ecosystems to promote nitrate removal.