Regulation of reactive nitrogen transport and transformation in contaminated environments

农业活动导致陆地流域内大量化学、辐射和生物活性氮（N）的释放迅速增加。 这些活性氮化合物在水质恶化中发挥着重要作用，它们通过土壤表面的含水无机氮物种（包括铵（NH 4+）和硝酸盐（NO3-））的沥滤损失，以及通过一氧化二氮（N2 O）排放增加而改变气候系统，一氧化二氮是一种强大而持久的温室气体和平流层臭氧消耗化合物。一氧化二氮是流域中NH 4+和NO3-转化的产物，因此通过这些物种的损失促进水质改善的流域区域可能会显示这种气体的排放量增加。当无机氮丰富时，这些氮的转化和交换受到氧化还原条件和温度的密切调节。 * 在实地研究中，由于淋溶的氮在农业流域产生的N2 O排放很少量化，因为实地研究往往侧重于直接影响点（即，土壤表面）。 然而，通过人类土地利用活动释放到土壤中的活性氮中有很大一部分被沥滤到相关的水生系统中，随后被去除或转化。产生N2 O的氮转化过程可以通过其独特的同位素指纹（即，d15 N和d18 O）。 由于稳定同位素是将N2 O分配到现场来源和/或转化过程的唯一手段，因此在未来十年中，稳定同位素可能会成为重要的监测工具，特别是考虑到现场便携式和高灵敏度N2 O同位素分析仪的最新进展。* 拟议的研究计划的目标是量化率和同位素特征的反应性N转换，导致N2 O排放量从温带农业为主的流域淋溶N经历高N负荷。 这将通过以下方式实现：选择现场站点，提供模型系统的特点淋溶氮负荷条件与农业活动;调查运输，转换，和同位素信号的水性无机氮化合物的前体N2 O在这些网站;研究率和同位素签名与N2 O释放在不同的氧化还原状态，热条件下，在这些网站和氮负荷水平;通过对碳基温室气体的同步分析，将N2 O排放置于流域研究点的总体全球升温潜能值的背景下;并确定所观察到的化学模式作为长期N2 O排放监测和缓解工具的效用。

Agricultural activities have led to a rapid growth in the release of a number of chemically, radiatively, and biologically reactive nitrogen (N) species within terrestrial watersheds. These reactive N compounds play important roles in the deterioration of water quality through leaching losses from soil surfaces of aqueous inorganic N species, including ammonium (NH4+) and nitrate (NO3-), and through changes to the climate system via increased emissions of nitrous oxide (N2O), a powerful and long-lived greenhouse gas and stratospheric ozone depleting compound. Nitrous oxide is a product of the transformation of both NH4+ and NO3- in watersheds, so watershed zones that facilitate improved water quality through losses of these species may show enhanced emissions of this gas. These N transformations and exchanges are closely regulated by redox conditions and temperature when inorganic N is abundant. ***Emissions of N2O in agricultural watersheds arising from leached N are seldom quantified in field studies, which tend to focus upon the point of immediate impact (i.e., soil surfaces). However, a significant proportion of reactive N released to soils through anthropogenic land use activities is leached into linked aquatic systems, where it is subsequently removed or transformed. Nitrogen transformation processes that generate N2O can be differentiated by their unique isotopic fingerprints (i.e., d15N and d18O). As stable isotopes provide the only means by which N2O can be apportioned to sources and/or transformation processes in the field, they are likely to factor in as crucial monitoring tools over the next decade, particularly in light of recent advances in the development of field portable and high-sensitivity N2O isotopic analyzers. ***The objective of the proposed research program is to quantify rates and characterize isotopic patterns of reactive N transformations that lead to N2O emissions from leached N in temperate zone agriculturally dominated watersheds experiencing elevated N loading. This will be accomplished by: selecting field sites that provide model systems for characterizing leached N loading conditions associated with agricultural activities; investigating the transport, transformation, and isotopic signals of aqueous inorganic N compounds that are precursors to N2O at these sites; studying the rates and isotopic signatures associated with N2O released under varying redox states, thermal conditions, and N loading levels at these sites; placing N2O release in the context of overall global warming potentials for the watershed points of study through concurrent analysis of carbon-based greenhouse gases; and identifying the utility of the observed chemical patterns for use as longer-term N2O emission monitoring and mitigation tools.**