Eutrophication of urban surface waters from excess nitrogen (N) and phosphorus (P) inputs remains a major issue in water quality management. Although much research has focused on understanding loading of nutrients from storm events, there has been little research to understand the contribution of baseflow, the water moving through storm drains between rainfall events. We investigated the relative contributions of baseflow versus stormflow for loading of water and nutrients (various forms of N and P) by the storm drain network in six urban sub-watersheds in St. Paul, MN, USA. Across sites, baseflow made substantial contributions to warm season (May–October) water yields (27–66 % across sites), total N yields (31–68 %), and total P yields (7–32 %). These results show that while P was predominantly delivered by stormflow, N loading was similar between baseflow and stormflow. We found that baseflow was dominated by groundwater inputs, likely caused by interception of shallow groundwater by storm drains, but also that variability in N and P among sites was related in part to the connectivity of the storm drains to upstream lakes and wetlands in some watersheds. The substantial loading by groundwater-dominated baseflow, especially for N, implies that N management may require a broader focus on N source reduction, perhaps through improved land management, in order to prevent contamination of shallow groundwater via infiltration.
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Acknowledgments This work was supported by grants from both the Institute on the Environment and the Water Resources Center at the University of Minnesota. The authors are especially grateful to the Capitol Region Watershed District for providing much of the data analyzed in this study, along with equipment, water samples, and expertise. We acknowledge in particular Matt Loyas for assistance with sample collection and data analyses, and Bob Fossum for feedback on the manuscript. We thank Marvin Bauer and Don Kilberg for the land cover data, Robert Tipping of the Minnesota Geological Survey for providing water table data, Anika Bratt and Ann Krogman for input on the manuscript, and Sandra Brovold, Jonathan Jaka, and Morgan Greenfield for collection and lab analysis of samples in the UMN data set.
© 2013, Springer Science+Business Media Dordrecht.
- Storm drains
- Urban biogeochemistry
- Urban hydrology