QUANTIFYING LEACHABLE PHOSPHORUS FROM COMMON URBAN TREE SPECIES

Abstract

Urban runoff containing high amounts of nutrients like nitrogen (N) and phosphorus (P) has long been established as a driver of surface water eutrophication. In residential areas, a primary source of nutrients is derived from leaf litter and other organic debris. P contained in leaves is leached and transported by stormwater to surface water at end-of-pipe locations. The majority of P from leaves is in the dissolved phase which can be difficult to remove using conventional treatment practices, leaving source control as the most viable option. Additional tools are needed to help forecast how different tree species may improve or hinder contributions of nutrients to runoff. For this reason, ten street tree species that are common throughout the contiguous U.S. were chosen to evaluate the effect of species and regional climate on leachable P from tree leaves. Laboratory experiments were conducted to characterize P leaching dynamics and models were developed to predict time variable P release from different species. After 48 hours, there were significant differences in the amount of P released by different species (ranged from 2.16 to 0.03 mg P g-1 leaf) and by the same species from different regions of the U.S. (ranged from 1.07 to 0.03 mg P g-1 leaf). There were also temporal variations in leaching across species; for example, in the first 12 hours of leaching, the percentage of maximum dissolved P released ranged from 5 to 90%. On average, more than half of the P was lost in the first 12 hours of exposure to water, making guided source control important to reduce inputs to surface water from key locations. Predictive equations describing P release over time were developed and used in conjunction with ArcGIS to identify locations in Madison, WI with high potential for P leaching from street trees. Results from this study can be used to provide an assessment of current conditions and help managers gain insight by proactively tailoring future planting scenarios and other source management practices that minimize nutrients in runoff.