Nitrogen Dynamics in a Salt Marsh

沿海泻湖型河口，如弗吉尼亚海岸保护区 通常是氮有限的。 获得的氮肥量 控制着河口的水生初级生产力。 的 农业径流对河口氮负荷的影响 在很大程度上取决于发生的N-循环过程 在潮间带沉积物中。 例如硝化作用- 反硝化作用导致沉积物中N的损失，而 异化硝酸盐还原为铵态氮， 在沉积物中。 努力开发模型来预测 氮流入河口的影响，由于自然或 人类活动受到了 参与测量各种氮循环的速率 湿地沉积物中的过程。 目前的许多技术 用来测量这些过程的速率是破坏性的， 使用有效性可疑的抑制剂，或要求 以高于环境浓度添加底物。 这样的技术最多可以测量潜力，而不是 原位反应速率。 本项目将开发应用15N所需的方法 同位素池稀释技术，以完整的沉积物岩心， 有植被和无植被的潮间带湿地生态系统。 这些测量将允许确定相对 硝化作用的重要性，其次是反硝化作用， 异化硝酸盐减少到总的N-预算。 该研究将在长期生态研究中心进行。 位于弗吉尼亚海岸保护区。 总的来说，这 信息将提高利率估计的准确性， 湿地和海岸沉积物中氮循环反应 并允许评估这些进程在 沿海海洋生态系统。

Coastal lagoon-type estuaries such as the Virginia Coast Reserve are often nitrogen-limited. The availability of nitrogen controls aquatic primary productivity in the estuary. The effects of N-loading on the estuary due to agricultural runoff depends to a large extent upon the N-cycling processes that occur in the intertidal sediments. Processes such as nitrification- denitrification result in losses of N from the sediment, whereas dissimilatory nitrate reduction to ammonium tends to conserve N in the sediment. Efforts to develop models to predict the effects of nitrogen influx to estuaries due to natural or anthropogenic processes have been limited by the difficulties involved in measuring the rates of the various N-cycling processes in wetland sediments. Many of the techniques currently used to measure the rates of these processes are disruptive, utilize inhibitors of questionable effectiveness, or require additions of substrates at higher than ambient concentrations. Such techniques may at best then measure potential rather than in-situ reaction rates. This project will develop the methodologies required to apply 15N isotope pool dilution techniques to intact sediment cores taken from vegetated and unvegetated intertidal wetland ecosystems. These measurements will allow the determination of the relative importance of nitrification, followed by denitrification v.s. dissimilatory nitrate reduction to the overall N-budget. The study will be performed at a Long Term Ecological Research site in the Virginia Coast Reserve. Taken together, this information will improve the accuracy of rate estimates of nitrogen cycling reactions in wetland and near shore sediments and permit an evaluation of the role of these processes in the ecology of coastal marine ecosystems.