Abstract Submission: In this project, we aggregated and analyzed stormwater and spatial data collected by cities, agencies, and watershed managers in Minnesota (USA) to understand how watershed and climate factors have influenced stormwater composition for Minnesota’s cities. We have assembled a database of nearly 15,000 sampled storm events from 90 piped storm drain sites across the Minneapolis-St. Paul Metropolitan Area, representing the outcome of monitoring efforts of over a dozen cities and watershed management organizations over the past 15-20 years. In addition to characterizing runoff concentrations of major stormwater pollutants, such as phosphorus, nitrogen, sediment, chloride, and heavy metals, we characterized watersheds using spatial data analysis and investigated sources of pollutants related to land cover and climate, as well as patterns of change over time in sites with the longest records. We present a few major insights from analysis of this unique dataset. Seasonal patterns in many pollutants were driven by snowmelt and vegetation dynamics, and concentrations of metals and phosphorus declined over time in several urban core sites, potentially impacted by national policies on emissions. High spatial variability was present in the dataset, as well. Duration of urbanization (as building age) was strongly related to both phosphorus and metals, though underlying mechanisms were likely different: while street tree canopy cover (a feature of older watersheds) was the most important factor affecting phosphorus, metal enrichment in older cities was consistent with a legacy of soil accumulation from paint and vehicle or industrial emissions.
