Collaborative Research: Revealing the Role of Less-Mobile Porosity in Hyporheic Denitrification and Greenhouse Gas Production

合作研究：揭示流动性较差的孔隙在潜流反硝化和温室气体产生中的作用

• 批准号: 1446375
• 负责人: Kamini Singha
• 金额: $ 8.89万
• 依托单位: Colorado School of Mines
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-03-01 至 2019-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1446375&HistoricalAwards=false
• 关键词: Collaborative; Research; Revealing; Role; Less

Streams and rivers have a remarkable cleansing function for natural and human generated contaminants, as microbes living in the streambed can transform these contaminants into less harmful compounds. Excess nitrogen in our terrestrial and aquatic ecosystems is now considered one of the greatest global-scale threats to humanity by degrading water quality and producing a powerful greenhouse gas. This research couples the cleansing function of rivers to this global excess nitrogen issue. Streambed bacteria can break down the reactive nitrogen compounds, primarily releasing non-reactive nitrogen gas that returns harmlessly to the atmosphere. However, a fraction is released as the strong greenhouse gas nitrous-oxide (N2O). Compelling data indicates pockets of longer-term water storage in streambeds, or microzones, create the low-oxygen conditions needed to both break-down dissolved nitrogen and form N2O. New remote sensing techniques of streambed microzones will allow us to better resolve the how nitrogen is attenuated and transformed through river transport, improving evaluations of watershed nutrient mitigation and helping better predict future climate change. Further, this research will dovetail with STEM education via community level partnerships with established outreach institutions. Outreach partners (Impression 5 Science Center and MSUSiFest) specialize in developing, executing and evaluating STEM exhibits and activities for children ages 4-12 and community "life-learners", both of which are key STEM demographics. Project PIs will connect with UConn undergraduate design teams and outreach partners to develop novel groundwater and streambed flow model exhibits and inquiry-based demonstrations designed to harness society's increasing fascination with real-time sensing and interaction. Outreach partners will use these products to illustrate principles of groundwater flow, contaminant transport, and greenhouse gas production, reaching 150,000+ students and community members each year.This project will link and quantify transient storage via dual-domain mass transport principles with the biogeochemical functions of stream sediments to reveal new insights on hyporheic denitrification and stream N2O production. This work is timely because recent global assessments reveal that rivers are major N2O producers, but the mechanism and spatial distribution of production remain unknown. Contrary to existing biogeochemical models for stream sediments, it is hypothesized that nitrate reduction to N2O occurs predominantly within streambed sediments that are oxic in a bulk sense but have local, anoxic less-mobile pore spaces. Largely overlooked in past work, these anoxic microsites must be mechanistically understood in order to upscale freshwater nitrogen dynamics from point, to reach, to basin scales. New observation methods and process-based models are needed to account for the role of anoxic microsites in fluid exchange and nitrogen biogeochemistry. Recently, project team members developed electrical geophysical methods for inference of less-mobile parameters, as the electric field can directly sense spatially variable solute dynamics in less-mobile porosity. Other team members have focused on developing labeled 15N tracer methods to reveal residence time controls on denitrification. These techniques will be combined to unlock the presence and function of anoxic microsites. The workplan comprises controlled laboratory experiments, numerical modeling, and field experiments at an established research site in the Ipswich Watershed, MA, USA. Our work will directly connect new process-based understanding to existing river network nitrate models, extending and capitalizing on previous NSF LINXII research. Specifically, the intrinsic properties of less-mobile pore space will be characterized, the existence of anoxic microsites and denitrification occurring in anaerobic microsites will be quantified, and multi-scale patterns of river nitrogen biogeochemistry will be enhanced. Overall, this work will transform the current understanding of hyporheic microsite processes, providing new mechanistic models of the role of hyporheic zones on watershed solute transport, nitrogen cycling and greenhouse gas production. The proposed research will address big questions about some very small places in our watersheds by quantifying hydrodynamic exchange with previously uncharacterized less-mobile hyporheic pore space.

溪流和河流对天然和人类产生的污染物具有显着的清洁功能，因为生活在流床中的微生物可以将这些污染物转化为有害的化合物。现在，我们的陆地和水生生态系统中过量的氮被认为是通过降低水质并产生强大的温室气体对人类最大的全球规模威胁之一。这项研究将河流的清洁功能融合到了这个全球过剩的氮问题上。溪流细菌可以分解反应性氮化合物，主要释放出无害返回大气的非反应氮气。但是，将部分释放为强烈的温室气氮氧化物（N2O）。引人注目的数据表明，流床或微区中的长期储水池会产生分解溶解的氮和形成N2O所需的低氧条件。流床微区的新遥感技术将使我们能够通过河流运输方式更好地解决氮的衰减和转化的方式，从而改善对流域养分减少的评估，并帮助更好地预测未来的气候变化。此外，这项研究将通过社区层面的合作伙伴与既定的外展机构相吻合。外展伙伴（Impression 5科学中心和MSUSIFEST）专门针对4-12岁儿童和社区“救生员”开发，执行和评估STEM展览和活动，这两者都是关键的STEM人口统计学。 PIS Project将与UConn本科设计团队和外展合作伙伴建立联系，以开发新颖的地下水和溪流流量模型展览以及基于查询的演示，旨在利用社会对实时感应和互动的持续着迷。外展伙伴将使用这些产品来说明地下水流量，污染物运输和温室气体生产的原理，每年达到15万多个学生和社区成员。该项目将通过双重域质量传输原理与临时群体链接和量化短暂的存储，并通过生物地球化学功能与流媒体剧集的生物质量功能来揭示有关高高压型DenItreciality n2O N2O的新见解。这项工作之所以及时，是因为最近的全球评估表明河流是主要的N2O生产者，但是生产的机制和空间分布仍然未知。与现有的溪流沉积物生物地球化学模型相反，据推测，硝酸盐还原至N2O主要发生在散装意义上有毒性但具有局部的，缺氧的较少摩托孔隙的流床沉积物中。在过去的工作中，这些缺氧的微镜在过去很大程度上都被忽略了，必须从机械上理解这些缺氧，以便从点，触及到盆地量表上的淡水氮动力学。需要新的观察方法和基于过程的模型来说明缺氧微圣从流体交换和氮生物地球化学中的作用。最近，项目团队成员开发了电地球物理方法来推断较不动的参数，因为电场可以直接在较不动的孔隙率中直接感知空间上可变的溶质动力学。其他团队成员则专注于开发标有15N示踪方法的标签，以揭示对硝化的停留时间控制。这些技术将被合并以解锁缺氧微座的存在和功能。该工作计划包括在美国马萨诸塞州伊普斯维奇水域建立的研究地点的受控实验室实验，数值建模和现场实验。我们的工作将直接将基于过程的新理解与现有的硝酸盐网络模型联系起来，从而扩展并利用了先前的NSF LinxII研究。具体而言，将表征较小的动物孔隙空间的内在特性，将量化厌氧微粒物中发生的缺氧微粒和反硝化的存在，并且将增强氮基生物地球化学的多尺度模式。总体而言，这项工作将改变当前对低音微材料工艺的理解，从而提供了新的机械模型，即低多层区域在流域溶质传输，氮气循环和温室气体产生中的作用。拟议的研究将通过量化流体动力交换，并用以前未经表征的较不动的低音孔隙空间来解决有关我们流域中一些非常小的地方的大问题。