NSF Award
2215300
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. <br/><br/>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.<br/><br/>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.
