CAS-Climate: SRS-- U.S.-China: Quantifying drivers of greenhouse gas evasion from aquatic systems along rural-urban transitions to enhance regional sustainability

世界许多地区的快速城市化导致了水通过地貌进入下游系统的方式发生了巨大变化。对溪流和河流进行渠化和管道化，建立滞流池塘，建立供水水库。城市水文系统的每一种操作主要是为了控制高流量的流量或时间，充其量只是次要考虑对水质的影响和其他环境影响，如温室气体(GHG)的产生。该项目旨在研究美国新罕布夏州东南部农村向城市过渡过程中水利基础设施对温室气体(GHG)的影响。然后，该项目将与中国科学家一起，将新汉普郡与北京的特大城市中国进行比较。总而言之，这两个项目将提供对湿润、温带气候下农村向城市过渡过程中城市化影响的全球范围的洞察。在这两个区域，城市水基础设施对水质和温室气体逃逸的影响在区域可持续性方面发挥着重要作用。在美国和中国的项目将与当地环境决策者广泛合作，他们负责通过管理水资源、养分负载和城市基础设施实现可持续性最大化。最终，该项目的目标是帮助实现联合国可持续发展目标12，“使城市和人类住区具有包容性、安全性、复原力和可持续性”，提供一个知识框架，最大限度地减少温室气体排放，作为城市到农村梯度水质管理的一部分。这项研究填补了目前对内陆水域在建筑环境的可持续性和生物地球化学功能中的作用的理解的空白。尽管广泛的研究证明，二氧化碳、甲烷和一氧化二氮这三种主要的温室气体在内陆地表水域中通常是过饱和的，但城市水环境的排放仍存在相当大的不确定性。关于从农村到城市的温室气体排放的变化，或具体的生物地球化学驱动因素(主要是氧气、养分和生物可用有机物的可用性及其对氧化还原条件的影响)，可能会改变温室气体排放的大小和主要温室气体之间的辐射强迫潜力的平衡，人们知道的更少。该项目将通过审查从农村到城市梯度的温室气体排放空间变异性的驱动因素来填补这一知识空白。将每月对溪流(自由流动溪流、有装甲堤岸或渠道的溪流以及管道溪流)、池塘和饮用水水库以及建造的滞留池塘中的温室气体浓度进行采样，并定期进行采样活动，以评估全天的变化。然后，将根据之前建立的水力几何形状、风速和逃避率之间的关系，使用测量的浓度来估计逃避率。该项目测试了这样一种假设，即由于水质的变化，城市水生系统比农村水生系统产生更多的温室气体，甲烷沸腾在城市环境中的总甲烷通量中扮演着特别重要的角色。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Rapid urbanization in many parts of the world has led to large changes in the way that water moves through the landscape into downstream systems. Streams and rivers are channelized and piped, runoff detention ponds are created, and water supply reservoirs are established. Each of these manipulations of the urban hydrologic system is conducted primarily to control the volume or timing of high flows, with at best only secondary consideration given to impacts on water quality and other environmental impacts such as production of greenhouse gases (GHG). This project addresses the impacts of water infrastructure on greenhouse gases (GHG) along the rural to urban transition of southeastern New Hampshire, USA. In conjunction with Chinese scientists, the project will then compare New Hampshire to the urban megacity of Beijing, China. Taken together, the two projects will provide insights into the global range of urbanization’s impacts along the rural to urban transition in humid, temperate climates. In both regions, the effects of urban water infrastructure on water quality and GHG evasion play an important role in regional sustainability. The projects in both the US and China will work extensively with local environmental decision-makers who have responsibility for maximizing sustainability through management of water resources, nutrient loading, and urban infrastructure. Ultimately the goal of the project is to help meet UN Sustainable Development Goal 12, “make cities and human settlements inclusive, safe, resilient and sustainable”, by providing a knowledge framework to minimize GHG production as part of water quality management along the urban to rural gradient. The research fills a gap in current understanding of the role of inland waters in the sustainability and the biogeochemical functions of the built environment. Although extensive work has documented that the three major GHGs, carbon dioxide, methane, and nitrous oxide, are typically supersaturated in inland surface waters, there is considerable uncertainty in emissions from urban aquatic environments. Even less is known about variation in GHG emissions across rural to urban gradients, or the specific biogeochemical drivers (principally the availability of oxygen, nutrients and bioavailable organic matter and the effects they have on redox conditions) that are likely to alter both the magnitude of GHG emissions and the balance of radiative forcing potential among the major GHGs. The project will fill this knowledge gap by examining the drivers of spatial variability in GHG emission across the rural to urban gradient. Concentrations of GHGs in streams (free-flowing streams, streams with armored banks or channels, and piped streams), ponds and drinking water reservoirs, and constructed detention ponds will all be sampled monthly and with periodic sampling campaigns to assess variation throughout the day. Measured concentrations will then be used to estimate evasion based on previously established relationships between hydraulic geometry, wind speed, and evasion rates. The project tests the hypothesis that urban aquatic systems produce more GHGs than their rural counterparts, due to changes in water quality, and that methane ebullition plays a particularly important role in total methane flux in the urban environment.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.