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

现场证据证实，活性氮（Nr）的流处理，主要是铵和硝酸盐，是强效温室气体一氧化二氮（N2O）的潜在重要来源。河流排放可能占全球人为一氧化二氮产量的10%，而每单位重量一氧化二氮的升温潜能值是二氧化碳的310倍。在河流中，N2O的产生主要发生在河床沉积物中，而反应物质（即溶解氧、Nr和有机碳）通过亚流的质量运输强烈影响反应速率、停留时间和随后的N2O排放。以前的研究表明，在潜流带（HZ）的水力学和河床形态之间有很强的相互作用。该项目结合了一种新颖的拉格朗日建模方法，该方法基于不同渠道河段类型的停留时间分布和河流网络的局部潜流成分，并在两个具有不同土地利用的流域进行季节性天气采样。更好地了解流域和网络规模对强效温室气体排放的控制，将对政策制定者解决地表水中Nr浓度升高的问题具有社会意义。研究成果将适用于土地利用管理、面源污染和河流修复工程。本研究成果将为估算河流网络尺度上Nr的命运提供一个模型，为HZ在河流网络尺度上的作用提供新的认识，并阐明河流网络结构和河流形态对HZ过程的影响。本研究的结果可以扩展到研究其他溶质和病原体沿河流的运输。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，因此在实地调查数据最少的情况下可用于提供预测。更广泛的影响还包括对高中生的推广，以及与McCall户外科学学校在气候变化背景下的工作交流。

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.