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，沿海污染的主要来源是地下水输送的氮（N），其主要来自废水、肥料和大气沉积物。这种含氮地下水从潮间带附近的渗流面进入沿海沃茨，或作为新鲜、微咸或含盐的海底地下水排放物直接流入海洋。根据土壤地球化学背景，去除固定N由于N2气体生产过程中在近海岸含水层可能会显着减弱陆源N负荷。除了对环境知之甚少外，我们对微生物氮转化去除固定氮的理解正处于转化过程中，这是由于最近发现了厌氧氨氧化（anammox）的新途径，这是一种微生物过程，可能非常重要，需要重新计算现有的全球氮预算。厌氧氨氧化提供了一种通过消除在N2气体产生之前硝化的需要来短路N循环的机制。令人信服的初步证据表明，厌氧氨氧化可能是一个重要的途径，二氮气体形成平流为主，粗，桑迪沉积物，三名年轻的科学家从伍兹霍尔海洋研究所将调查的后果，平流通过可渗透的沉积物对N的运输和转换。 他们将采用一系列旨在模拟通过可渗透海洋沉积物的水运输的实验，并利用一种结合同位素配对和膜入口质谱技术的新方法来量化和识别N2生产的所有途径。 新的方法是必要的，因为目前可用的程序测量N2生产是不足以区分可能发生在这些系统中的反应途径。该项目将有助于更好地了解地下水输送的氮负荷的行为和内部N循环的大部分沿海沃茨和大陆架地区的特征是渗透性沉积物，从而造福社会。到2020年，预计世界上75%的人口将居住在海岸线35英里以内，因此我们必须了解人为污染物如何在环境中从陆地转移到海洋。拟议的项目还将通过让高中生和本科生实习生参与实验室和实地研究来促进教育。

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.