Denitrification and nitrous oxide production in aquatic systems

我的研究项目的目标是更好地理解水生系统中的主要元素循环。对水生系统的氮负荷是这些生态系统中最普遍的化学污染形式。这些氮的一部分可以通过反硝化（将硝酸盐还原为N2）去除，因此反硝化具有改善水质的潜力。然而，反硝化的副产品N2O是一种强有力的温室气体。水生系统已经是一氧化二氮的一个重要来源，随着全球氮肥使用的增加，预计这一来源还会增加，因此水生系统的氮污染也会增加。反硝化的最终产物是气体，这使得测量油田的生产率具有挑战性。因此，大多数关于反硝化和N2O生成的研究都是台台规模的，缺乏自然系统的生态复杂性。在这个尺度上，不可能确定影响反硝化的更高层次的物理、生物或化学因素的重要性。因此，我们对湖泊作为氮汇和N2O源的重要性知之甚少。这使得制定有效的营养物流域管理计划或在全球变暖模型中限制温室气体生产的全球预算变得困难。本文提出了一种在全系统尺度上测量湖泊反硝化和N2O生成的方法。这种方法基于对溶解气体（N2和N2O）的高精度测量、湖泊混合模型和模拟的大气通量。这种方法应该可以为湖泊每年产生和排放的这些气体建立非常准确的预算。我实验室的学生将使用这种方法来研究湖泊的各种生物（群落结构）、化学（元素比）和物理属性作为反硝化和N2O生成速率的潜在决定因素的作用。

The goal of my research program is to better understand major elemental cycles in aquatic systems.  Nitrogen loading to aquatic systems is the most pervasive form of chemical pollution in these ecosystems.  Some fraction of this nitrogen can be removed by denitrification (reduction of nitrate to N2), thus denitrification has the potential to improve water quality. However, a byproduct of denitrification, N2O, is a potent greenhouse gas.  Aquatic systems are already a significant source of nitrous oxide and this source is projected to increase as global use of nitrogen fertilizers, and therefore nitrogen pollution of aquatic systems, increases.  The end-products of denitrification are gases, making it challenging to measure rates of production in the field. As a result, most research on denitrification and N2O production is bench-top scale, lacking the ecological complexity of natural systems.  At this scale, it is not possible to determine the importance of higher-level physical, biological, or chemical factors that affect denitrification. We, therefore, know little about how important lakes are as sinks for nitrogen and sources for N2O.  This makes it difficult to devise effective watershed management plans for nutrients, or to constrain the global budget for greenhouse gas production in global warming models.I propose an approach to measure denitrification and N2O production in lakes at the whole-system scale. This approach is based on high-precision measurements of dissolved gases (N2 and N2O), lake mixing models, and modeled atmospheric flux. This approach should make possible construction of very accurate budgets for annual production and emissions of these gases from lakes. Students in my laboratory will use this approach to study the roles of various biological (community structure), chemical (elemental ratios), and physical attributes of lakes as potential determinants of denitrification and N2O production rates.