Collaborative Research: Novel interdisciplinary flume experiments to investigate the role of the hyporheic zone in greenhouse gas generation

合作研究：新的跨学科水槽实验，以调查潜流带在温室气体产生中的作用爱达荷大学的丹尼尔·托尼纳凯文·费里斯和博伊西州立大学的肖恩·本纳潜流带是溪流周围的饱和沉积物带，在那里溪流水与孔隙水混合。这个区域在氮循环中起着重要的作用，氮循环已经被人为的食物和能源生产从根本上改变了。此外，该区域可能是强效温室气体一氧化二氮（N2O）的重要来源，潜在排放量高达0.7 Tg y-1，相当于全球人为N2O排放量的10%。虽然潜流交换的程度受到河流流量和河床地形的强烈影响，但这些物理过程与由此产生的微生物介导的导致N2O生成和释放的地球化学反应之间的关系仍然知之甚少。这项跨学科研究的目标是了解、量化和参数化河床水力学和形态对潜流带N2O排放的影响。通过反硝化作用生成N2O主要发生在有催化微生物群落存在的河床沉积物中。因此，氧气、硝酸盐、铵和N2O通过低氧流的质量运输强烈影响反应速率、停留时间和随后的N2O产量。推而言之，河流流量和河道形态可能控制N2O生成速率，并可能有效预测N2O生成速率。然而，许多重要的原位过程仍然知之甚少。例如，与N2相比，活性氮转化为N2O的量非常小（0-6%），但高度不确定，部分原因是对优势微生物群落的遗传组成和影响其分布和活动的水文因素的不完全了解。此外，在自然系统中，对原位活性氮生成的贡献与河流输送的贡献的控制不容易确定。事实上，自然系统固有的时空复杂性限制了传统观测方法的强度，并排除了在预测数学模型中明确表达这些相互作用的可能性。为了克服传统野外观测方法的局限性，本研究将采用一系列可操作的大型水槽实验。大规模水槽实验将提供前所未有的控制，同时保持本质上重要的变量，如现实的微生物群落，水组成，水流和渠道结构。该研究将对地表-地下水交换、氮转化和潜流区N2O排放之间的基本相互作用产生新的认识。它将通过数值分析模型和水槽实验，通过耦合潜流水力学和生化反应来解释潜流区作为生化转化区的作用。这项工作的结果将作为在流域尺度上模拟河流N2O排放的基础。因此，控制操作实验的第一阶段对于大规模提高我们对水资源的认识至关重要。

Collaborative Research: Novel interdisciplinary flume experiments to investigate the role of the hyporheic zone in greenhouse gas generationDaniele Tonina, University of Idaho Kevin Feris and Shawn Benner, Boise State UniversityThe hyporheic zone is the band of saturated sediment surrounding the stream, where stream waters mix with pore-water. This zone plays an important role in the nitrogen cycle, which has been radically altered by anthropogenic food and energy production. Furthermore, this zone may be a significant source of the potent greenhouse gas nitrous oxide (N2O), potentially emitting for up to 0.7 Tg y-1, equivalent to 10% of global anthropogenic N2O emissions. While the degree of hyporheic exchange is strongly influenced by stream flow and streambed topography, the relationship between those physical processes and the resulting microbially-mediated geochemical reactions leading to N2O generation and release remains poorly understood. The goal of this interdisciplinary research is to understand, quantify, and parameterize the influence of streambed hydraulics and morphology on the emission of N2O from the hyporheic zone. The generation of N2O via denitrification primarily occurs within the streambed sediments where the catalyzing microbial community is present. Therefore, the mass transport of oxygen, nitrates, ammonium and N2O by hyporheic flow strongly influences reaction rates, residence times, and subsequent N2O production. By extension, stream flow and channel morphology presumably control, and may be effective predictors of, N2O generation rates. However, a number of important in-situ processes remain poorly understood. For example, the amount of reactive nitrogen converted to N2O versus N2 is quite small (0-6%) but highly uncertain, due in part to an incomplete understanding of the genetic composition of the dominant microbial community and the hydrologic factors affecting their distribution and activity. Additionally, controls on the contribution of in-situ reactive nitrogen generation vs. that delivered by the stream are not easily determined in natural systems. Indeed, the inherent spatiotemporal complexity of natural systems limits the strength of traditional observational approaches and precludes explicit expression of these interactions in predictive mathematical models. To overcome limitations of traditional observational field approaches, this research will use a series of manipulative large-scale flume experiments. Large-scale flume experiments will provide unprecedented control while maintaining intrinsically important variables such as a realistic microbial community, water composition, stream flow, and channel structure. This research will develop new understanding of the fundamental interaction among surface-subsurface water exchange, nitrogen transformation and N2O emissions from the hyporheic zone and ultimately from streams. It will explain the role of the hyporheic zone as a biochemical transformation zone by coupling hyporheic hydraulics to biochemical reactions, through numerical-analytical models and flume experiments. Results from this work will act as building blocks for modeling N2O emissions from streams at the watershed scale. Thus, this first stage of controlled manipulative experimentation is essential in advancing our knowledge of water resources at the large scale.