Abstract
Trees are ubiquitous in urban environments and are appreciated for a range of ecosystem services. However, the tradeoff in their ability to reduce stormwater runoff volumes versus their potential contributions of nutrient and coarse organic matter in dissolved and particulate forms has been largely ignored in stormwater management practices due to lack of robust data. Our project has now filled some of these data gaps through a three-year monitoring effort to quantify tree-scale water quantity and quality fluxes across eighteen ash (Fraxinus spp.) trees and four maple (Acer spp.) trees in the city of St. Paul. We also examine how these local measurements and seasonal patterns relate to corresponding watershed-level stormwater observations. Our results revealed that throughfall nutrient fluxes were higher under trees than in open precipitation, despite an overall reduction in water volumes due to canopy interception. Nevertheless, these nutrient contributions can potentially be mitigated through improved tree health, which also increases soil water uptake through enhanced evapotranspiration. Finally, leaf litter nutrient content progressively declined closer to the pavement curb, suggesting that trees near and overhanging impervious road surfaces can contribute throughfall nutrient fluxes that quickly enter the stormwater network.
Xue Feng (right) is an Associate Professor in the Department of Civil, Environmental, and Geo- Engineering at the University of Minnesota and an affiliate faculty at the Saint Anthony Falls Laboratory. Her research aims to advance understanding of the interactions between vegetation, climate, and the water cycle, and use it to improve Earth system modeling and watershed management. She is a recipient of the NOAA Climate and Global Change Postdoctoral Fellowship, a U.S. National Science Foundation CAREER Award, a McKnight Land-Grant Professorship, and the Deborah L. Swackhamer Early Career Award.
Dr. Diana Karwan (left) is an Associate Professor in the Department of Forest Resources at the University of Minnesota. Her research examines how landscapes, land use, and vegetation relate to surface water quantity and quality. Many of her research studies and publications center on sediment and related contaminant transport through watersheds in response to land use and climate changes. She is a recipient of a National Science Foundation Postdoctoral Fellowship. She is currently an affiliate scientist of the Minnesota Center for Prion Research and Outreach, with whom she was inducted into the University of Minnesota’s Academy for Excellence in Team Science in 2022.
Panelists:
- Dustin Ellis, Forestry Supervisor, Hennepin County
- Mirae Guenther, Water Resources Data Analyst, Mississippi Watershed Management Organization