Integrating biogeochemistry and physics to understand hot spots and hot moments for nitrogen transformation in lakes and reservoirs

在世界各地的许多水道中，营养氮的过度富集是一个主要且日益严重的问题。除了使饮用水退化外，高浓度还会减少生物多样性，增加有害藻华的频率，并导致低氧（“死区”），从而破坏生态系统。如果没有生活在水生生态系统中的水生微生物，与氮有关的问题将会严重得多，水生微生物通过将有害的氮从营养物质转化为可返回大气的溶解气体来清除有害的氮。这种去除过程被称为反硝化，对污染管理很重要，但在湖泊和水库等复杂系统中，导致高反硝化率的条件尚不清楚。反硝化速率很难测量，而且在空间和时间上变化很大，这一事实阻碍了理解的进展。该项目通过结合最先进的物理和生物地球化学技术，以一种新的方式测量湖泊的反硝化作用，解决了这些挑战。将在本项目中加以改进和应用的新的通量梯度测量技术有可能解决反硝化的时空变化，并将用于对可能控制反硝化速率的人类活动和自然水文过程有新的认识。预计该项目将提高测量、解释、预测甚至控制反硝化的能力，从而使湖泊和河流的水质得到改善。拟议的研究不仅旨在促进基本的科学理解，而且还提供与管理相关的结果，帮助解决紧迫的社会问题。例如，人们希望对水库营养物处理的新见解将使管理者能够改进他们对水资源和相关生态系统的管理。为了帮助研究人员和管理人员应用通量梯度技术，将开发一个多媒体网站，解释该方法并详细说明重要的实践和方法考虑因素。该项目还将产生教育影响：将直接支持至少2名博士生和3名本科生。

In many waterways around the world, over-enrichment with the nutrient nitrogen is a major and growing concern. In addition to degrading drinking water, high levels damage ecosystems by reducing biodiversity, increasing the frequency of harmful algal blooms, and contributing to low oxygen ("dead zones"). Nitrogen-related problems would be substantially worse if not for the aquatic microbes that live in aquatic ecosystems and remove harmful nitrogen by converting it from a nutrient to a dissolved gas that can return to the atmosphere. This removal process, called denitrification, is important for pollution management, but the conditions that result in high rates of denitrification are not well known in complex systems such as lakes and reservoirs. Progress in understanding has been hampered by the fact that denitrification rates are challenging to measure, and vary greatly in space and time. This project addresses these challenges by combining state-of-the-art physical and biogeochemical techniques in a new way to measure denitrification in lakes. The new flux-gradient measurement technique that will be refined and applied in this project has potential to resolve spatial and temporal variation in denitrification, and will be used to shed new light on the human activities and natural hydrologic processes that probably control denitrification rates. It is expected that this project will improve the ability to measure, explain, predict, and perhaps even control denitrification so that lakes and the rivers draining them will have improved water quality. The proposed research is designed not only to advance fundamental scientific understanding, but also to provide management-relevant results that help address pressing societal concerns. For example, it is hoped that new insights into reservoir nutrient processing will allow managers to improve their management of water resources and associated ecosystems. To help researchers and managers apply the flux-gradient technique, a multi-media website will be developed, explaining the approach and providing detail on important practical and methodological considerations. This project will also have an educational impact: at least 2 doctoral students and 3 undergraduates will be directly supported.