Urban Tree Canopy Effects on Water Quality via Inputs to the Urban Ground Surface

Abstract

Urban trees have diverse effects on hydrologic processes, influencing water quality within and downstream of the city. Urban trees, which include street trees, trees on private property, and those in urban forests, parks, and arboreta, intercept and modify precipitation before it reaches the ground. Urban canopies alter precipitation chemistry through interaction with atmospheric components such as ions and particles, uptake and leaching, and within-canopy production of materials. Due to numerous sources of nutrients and pollutants in urban areas, trees often act to concentrate chemical inputs to the urban ground surface, though this effect varies depending on such factors as urban form and tree species. Ultimately, the effect of the urban tree canopy on the urban hydrologic cycle is a complex topic with intertwined socio-ecological causes and effects. While the scientific community has been exploring this topic for the last 40 years, there is still much work to be done to describe the effects of the urban tree canopy on urban water quality and to use this understanding to maximize urban tree canopy benefits.