The dynamics of water in arid cities, Part II: Effects of stormwater infrastructure on dissolved and particle-bound nutrient transport across multiple spatial scales

Background/Question/Methods

Over recent years urbanization has occurred rapidly, in particular in arid regions of the USA. Major changes in ecosystem structure occur during urbanization, including changes in land cover, especially impervious surfaces, and hydrological flow paths due to the construction of stormwater infrastructure.  These changes may have considerable implications for nutrient transport and redistribution within the urban ecosystem. In this study we investigate the effects of urban stormwater infrastructure on storm hydrographs and the hydrologically mediated transfer of dissolved and particulate nitrogen (N), phosphorus (P), and carbon (C) at multiple spatial scales. Storms were sampled in 11 hierarchically nested catchments, ranging in size from 5 ha to 17000 ha, in the Indian Bend Wash catchment in Scottsdale, Arizona, from summer 2010 to winter 2011.  We contrast intense, spatially discrete summer monsoonal storms with less intense winter rainfall events that have broader spatial coverage.

Results/Conclusions

For N, P, and C, particle-bound nutrient transport accounts for a significant proportion of total nutrient flux. The transport of dissolved and particulate N, P, and C is governed primarily by flow characteristics, which vary depending on the extent and type of stormwater infrastructure. Across all sites, at high discharges the proportion of nutrients in particulate forms increases because of the increased capacity of flow to entrain and transport particulate organic material and sediment. The total export of dissolved and particle-bound materials from catchments increases with spatial scale, but export of materials per unit area actually decreases with an increase in spatial scale. There is discernible variation in mid-scale export of particulate material due to differences in stormwater infrastructure, with lowest exports from catchments with retention basins. Thus, changes in ecosystem structure resulting from designed ecosystems with different types of stormwater infrastructure exert a major control over the dynamics of particulate and dissolved nutrient redistribution within these catchments.