Spatial Distribution of Critical Source Areas for Non-Point Source Pollution in Urban Watersheds

Abstract Submission: Targeting non-point source pollution at its origin is gaining attention as an effective strategy for improving water quality and stormwater control measures placement. However, the identification and spatial distribution of critical source areas (CSA)—locations that disproportionately contribute to NPS pollution generation —within urban watersheds have not been extensively studied. This research focuses on the identification and spatial distribution of CSAs in three small urban watersheds (East Kittsondale, Como 3, and Trout Brook-East Branch) in the Twin Cities metro area, Minnesota using the Soil and Water Assessment Tool (SWAT). The models were calibrated and validated using observed weather, runoff, and pollutant data from 2005 to 2022.
The results showed that 50%, 75%, and 90% of sediment yield from the East Kittsondale watershed originated from 15%, 39%, and 64% of the watershed area, respectively. These 50%, 75%, and 90% load contribution values were 31%, 57%, and 77% of the watershed area, respectively, for dissolved nitrogen and 22%, 47%, and 71%, respectively, for dissolved phosphorus. Particulate phosphorus load was highly concentrated in CSAs, with 50%, 75%, and 90% of the pollution generated from only 9%, 25%, and 50% of the watershed area, respectively. Notably, 90% of surface runoff came from less than 45% of the watershed. The developed methodology is transferable to other urban watersheds, providing significant insights for optimizing the design and placement of stormwater control measures and the development of watershed management plans.

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