Mechanisms of Dinitrogen Production in Coastal Permeable Sediments

在具有高水力传导性土壤和可渗透海洋沉积物的沿海流域，沿海污染的一个主要来源是地下水输送的氮(N)，它主要通过废水、化肥和大气沉积添加到含水层中。这些含氮地下水从潮间带附近的渗漏面进入沿海水域，或作为淡水、微咸水或咸水海底地下水排放直接流入海洋。根据生物地球化学环境的不同，近岸含水层中氮气产生过程对固定氮的清除可能会显著减少陆源氮负荷。除了对环境知之甚少外，由于最近发现了厌氧氨氧化(Anammox)的新途径，我们对微生物氮转化去除固定氮的理解也处于转变过程中，这一微生物过程可能如此重要，以至于需要重新计算现有的全球氮收支。Anammox通过消除氮气产生之前的硝化作用，提供了一种短路N循环的机制。基于令人信服的初步证据，Anammox可能是平流主导的粗砂质沉积物中氮气形成的重要途径，来自伍兹霍尔海洋研究所的三名年轻科学家将研究通过可渗透沉积物的平流对N迁移和转化的影响。他们将采用一系列旨在模拟水在可渗透海洋沉积物中传输的实验，并利用一种结合同位素配对和膜进气质谱仪技术的新方法来量化和识别氮气产生的所有途径。新的方法是必要的，因为目前测量氮气产量的现有程序不足以区分这些系统中可能发生的反应途径。拟议的项目将有助于更好地了解地下水输送的氮负荷的行为，以及大部分沿海水域和以可渗透沉积物为特征的大陆架区域内的内部氮循环，从而使社会受益。到2020年，预计将有75%的世界人口居住在离海岸线35英里的范围内，因此，至关重要的是，我们必须了解人为污染是如何从陆地输送到海洋的。拟议的项目还将通过让高中生和本科生实习生参与研究的实验室和现场方面来促进教育。

ABSTRACTOCE-0524994In coastal watersheds with soils of high hydraulic conductivity and permeable marine sediments, a major source of coastal pollution is groundwater-transported nitrogen (N), which is added to the aquifer primarily from wastewater, fertilizers, and atmospheric deposition. This nitrogen-bearing groundwater enters coastal waters from a seepage face near the intertidal zone or flows directly into the sea as fresh, brackish or saline submarine groundwater discharge. Depending on the biogeochemical setting, removal of fixed N due to N2 gas producing processes in the near shore aquifer may significantly attenuate land-derived N loads. In addition to the environment being poorly understood, our understanding of microbial nitrogen transformations for removal of fixed nitrogen is in the process of transformation due to recent discovery of the new pathway of anaerobic ammonium oxidation (anammox), a microbial process that may be so significant as to require recalculation of existing global N budgets. Anammox provides a mechanism for short-circuiting the N cycle by eliminating the need for nitrification prior to N2 gas production. Based on compelling preliminary evidence that anammox may be an important pathway for dinitrogen gas formation in advection dominated, coarse, sandy sediments, three young scientists from the Woods Hole Oceanographic Institution will investigate the consequences of advection through permeable sediments on N transport and transformations. They will employ a series of experiments designed to simulate water transport through permeable marine sediments and utilize a new approach that combines of isotope pairing and membrane inlet mass spectrometry techniques to quantify and identify all pathways of N2 production. The new approach is required as currently available procedures for measuring N2 production are not adequate to distinguish among the reaction pathways that may be occurring in these systems. The proposed project will benefit society by helping to develop a better understanding of behavior of groundwater-transported N loads and of internal N cycling within the large proportion of coastal waters and continental shelf areas characterized by permeable sediments. With 75% of the world's population expected to live within 35 miles of a coastline by 2020, it is vitally important that we understand how anthropogenic contamination is transformed in the environment as it is transported from land to the ocean. The proposed project will also foster education by involving high school students and undergraduate interns in both laboratory and field aspects of the research.