URBAN STREET TREE LITTER IS A KEY DRIVER OF STORMWATER NUTRIENT CONCENTRATIONS AND YIELDS THROUGHOUT THE YEAR

Street trees in urban environments can be important conduits for nutrients to stormwater; they take up nitrogen (N) and phosphorus (P) from soils and deposit them onto streets in the form of litterfall. These nutrients can rapidly enter stormwater in dissolved and particulate forms, contributing to eutrophication of receiving waters. Our goal was to quantify the contribution of street tree litterfall to stormwater nutrient concentrations and yields. Using data from high-frequency street sweeping programs in the Twin Cities Metro Area (TCMA), we modeled the relationship between percent canopy cover over streets and the mass of litter N and P swept across seasons. We used these relationships to estimate litter-associated N and P deposited onto streets based on average tree canopy cover over streets, then compared these estimates to observed nutrient yields and concentrations from 12 TCMA watersheds. We predicted that litterfall contributes an average of 76% and 67% of stormwater N and P yields during the snow-free season, with the greatest contributions in the spring and fall. Predicted contributions from litterfall ranged greatly between watersheds (36–140% for N and 7–115% for P) likely due to factors influencing stormwater runoff volume and nutrient retention. Estimated litterfall-associated nutrients were a significant predictor of stormwater N and P concentrations across all seasons. These findings suggest that street sweeping and street tree management can be tools to address excess nutrients in urban freshwaters.

Primary Presenter: Erin Mittag, University of Minnesota (mitta062@umn.edu)

Authors:

Erin Mittag, University of Minnesota  (mitta062@umn.edu)

Sarah Hobbie, University of Minnesota  (shobbie@umn.edu)

Jacques Finlay, University of Minnesota  (jfinlay@umn.edu)

Ben Janke, University of Minnesota  (janke024@umn.edu)

Paula Kalinosky, Minnesota Pollution Control Agency  (paula.kalinosky@state.mn.us)

Rachel King, National Center for Ecological Analysis and Synthesis  (rking@nceas.ucsb.edu)

Lawrence Baker, University of Minnesota  (baker127@umn.edu)

Tessa Belo, Washington State University  (belox004@umn.edu)

Christopher Buyarski, University of Canterbury  (chris.buyarski@canterbury.ac.nz)

Ross Bintner, City of Edina, MN  (rbintner@EdinaMN.gov)