Collaborative Research: Understanding the role of hyporheic processes on nitrous oxide emissions at the stream network scale

合作研究：在河流网络尺度上了解湿法过程对一氧化二氮排放的作用现场证据证实，对活性氮(Nr)(主要是氨和硝酸盐)的河流处理是强有力的温室气体一氧化二氮(N2O)的潜在重要来源。水蒸气排放可能占全球人为N2O排放量的10%，而N2O单位重量的变暖潜力是二氧化碳的310倍。在河流中，N2O的产生主要发生在河床沉积物中，活性物质(即溶解氧、Nr和有机碳)通过地下水流的质量传输强烈影响反应速率、停留时间和随后的N2O排放。以往的研究已经表明，河床形态与潜流带(HZ)的水力学有很强的相互作用。该项目将一种新的拉格朗日建模方法与两个土地利用不同的流域的季节性天气采样相结合，该方法基于区分河道河段类型和局部河网次生成分的停留时间分布。增进对有效温室气体排放的分水岭和网络规模控制的理解，将对解决地表水中Nr浓度升高的政策制定者具有社会意义。研究成果将应用于土地利用管理、面源污染、河流修复等项目。本研究的成果将为在河流网络尺度上估算Nr的去向提供一个模型，对HZ在河流网络尺度上的作用有一个新的认识，并阐明河流网络结构和河流形态对HZ过程的影响。这项研究的结果可以推广到研究其他溶质和病原体沿溪流的传输。随着遥感和地理信息系统工具的进步，这种方法的数据将更容易获得，从而适用于在只有最少的实地调查数据时提供预测。更广泛的影响还包括与高中生的接触，以及与麦考尔户外科学学校在气候变化背景下交流工作的工作。

Collaborative Research: Understanding the role of hyporheic processes on nitrous oxide emissions at the stream network scale Field evidence confirms that stream processing of reactive nitrogen (Nr), primarily ammonium and nitrate, is a potentially important source of the potent greenhouse gas nitrous oxide (N2O). Stream emissions may account for up to 10% of global anthropogenic N2O production and N2O has 310 times more warming potential per unit weight than carbon dioxide. In streams, the production of N2O occurs primarily in streambed sediments, and the mass transport of reactive species, i.e., dissolved oxygen, Nr, and organic carbon, via hyporheic flow strongly influences reaction rates, residence times, and subsequent N2O emissions. Previous research has shown a strong interaction between hydraulics in the hyporheic zone (HZ) and streambed morphology. The project couples a novel Lagrangian modeling approach based on residence time distributions differentiated for channel reach types and local hyporheic components of the stream network with seasonal synoptic sampling in two watersheds with contrasting land use. Improved understanding of watershed and network scale controls on potent greenhouse gas emissions will be societally-relevant to policy makers addressing elevated Nr concentrations in surface waters. Research results will be applicable to land use management, non-point source pollution, and river restoration projects. The products from this research will provide a model for estimating the fate of Nr at the stream network scale, offer a new understanding of the role of HZ at the stream network scale, and clarify the effect of stream network structure and stream morphology on HZ processes. Results from this research can be extended to study transport of other solutes and pathogens along streams. With the advance in remote sensing and GIS tools, data for this approach will be more readily available and thus applicable to provide predictions when minimal field survey data are available. The broader impacts also involve the outreach to high school students, and the work with the McCall Outdoor Science School in regards to communication of the work in a climate change context.