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，以调查低渗区在温室气体产生中的作用爱达荷大学的Daniele Tonina，Kevin Feris和博伊西州立大学的Shawn Benner低渗区是河流周围的饱和沉积物带，溪水与孔隙水混合在一起。这一区域在氮循环中扮演着重要的角色，而人类的食物和能源生产已经从根本上改变了氮循环。此外，该地区可能是强有力的温室气体一氧化二氮(N2O)的重要来源，潜在排放量高达0.7Tg/y-1，相当于全球人为N2O排放量的10%。尽管水体交换程度受水流和河床地形的强烈影响，但这些物理过程与导致N2O产生和释放的微生物介导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和形态对潜流带N2O排放的影响。通过反硝化作用产生N2O主要发生在河床沉积物中，那里存在催化微生物群落。因此，潜流对氧气、硝酸盐、氨氮和N2O的传质对反应速率、停留时间和后续的N2O产生有很大影响。推而广之，水流和河道形态可能控制着N2O的生成速率，并且可能是有效的预测因子。然而，一些重要的原位过程仍然知之甚少。例如，与氮气相比，转化为N2O的活性氮量很少(0-6%)，但非常不确定，部分原因是对优势微生物群落的遗传组成以及影响其分布和活动的水文因素了解不完全。此外，在自然系统中，对原位活性氮生成与河流输送的活性氮的贡献的控制并不容易确定。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力量，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。为了克服传统观测场方法的局限性，本研究将采用一系列可操纵性的大型水槽实验。大型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、溪流流量和河道结构。这项研究将对地表-地下水交换、氮素转化和来自潜流带并最终来自河流的N2O排放之间的基本相互作用产生新的理解。它将通过数值分析模型和水槽实验，通过将潜流水力与生化反应相耦合来解释潜流带作为生化转换区的作用。这项工作的结果将作为建立流域尺度河流N2O排放模型的基础。因此，这一受控操纵实验的第一阶段对于在大范围内推进我们对水资源的认识是必不可少的。

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.