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

世界上许多地区的快速城市化导致了水在景观中流向下游系统的方式发生了巨大变化。溪流和河流被渠化和管道化，形成了蓄流池，并建立了供水水库。对城市水文系统的每一种操纵都主要是为了控制大流量的数量或时间，对水质的影响和其他环境影响，如温室气体的产生，充其量只是次要的考虑。本项目研究了美国新罕布什尔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。在与中国科学家的合作下，该项目将把新罕布什尔州与中国的大城市北京进行比较。总而言之，这两个项目将深入了解湿润、温带气候下农村向城市过渡过程中城市化对全球范围的影响。在这两个区域，城市水基础设施对水质和温室气体减排的影响在区域可持续性中发挥着重要作用。美国和中国的项目将与当地环境决策者广泛合作，他们有责任通过管理水资源、营养负荷和城市基础设施来最大限度地提高可持续性。该项目的最终目标是帮助实现联合国可持续发展目标12，即“使城市和人类住区具有包容性、安全性、复原力和可持续性”，通过提供一个知识框架，将温室气体的产生降至最低，作为城乡梯度水质管理的一部分。该研究填补了目前对内陆水域在可持续性和建筑环境的生物地球化学功能中的作用的理解空白。尽管大量的工作已经证明，三种主要的温室气体——二氧化碳、甲烷和一氧化二氮——在内陆地表水中通常是过饱和的，但城市水环境的排放存在相当大的不确定性。对于农村到城市梯度的温室气体排放的变化，或者可能改变温室气体排放规模和主要温室气体之间辐射强迫势平衡的特定生物地球化学驱动因素（主要是氧气、营养物和生物可利用有机质的可用性及其对氧化还原条件的影响），我们所知甚少。该项目将通过研究农村到城市梯度中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。溪流（自由流动的溪流、有装甲河岸或渠道的溪流和管道溪流）、池塘和饮用水水库以及建造的蓄水池中的温室气体浓度都将每月取样，并定期取样，以评估全天的变化。然后，测量的浓度将用于根据先前建立的水力几何形状、风速和逃逸率之间的关系来估计逃逸。该项目验证了以下假设：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，而甲烷沸腾在城市环境中的甲烷总通量中起着特别重要的作用。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.