Stormwater Nitrogen in Arizona (SNAZ): runoff and stormwater-mediated export from urbanized catchments within the greater Phoenix metropolitan area, Arizona, USA (2010-2012)

Urbanization alters dramatically watershed ecosystem processes. Land-use change and anthropogenic activities contribute to increased inputs of nutrients and other materials, while changes to land cover alter hydrology and the corresponding movement of materials. These changes have ramifications for both watershed processes and downstream systems. The impacts of urbanization on aquatic systems are well-studied, and frequently encapsulated in the ‘urban stream syndrome’ (Walsh et al. 2005) that describes, among others, increased nutrient loading and stream flashiness. However, there is some evidence that aridland cities behave differently (Grimm et al. 2004, 2005), and the complex dynamics among catchment characteristics, storm attributes, and runoff in highly urbanized settings of the arid Southwest remains poorly understood. To enhance our understanding of stormwater dynamics and watershed functioning in aridland, urban environments, the Central Arizona–Phoenix Long-Term Ecological Research (CAP LTER) program began monitoring stormwater runoff at the outflow of the Indian Bend Wash (IBW) in 2008. The IBW is a tributary to the Salt River in central Arizona, and is a major drainage within the greater Phoenix metropolitan area, encompassing much of the City of Scottsdale. A model of soft engineering, the IBW as it runs through much of the City of Scottsdale is comprised largely of a series of artificial lakes, parks, paths, golf courses, ball fields, and other non-structural elements designed with the dual roles of providing outdoor amenities to the City residents while serving as an effective flood water conveyance feature. A unique biogeochemistry of this novel system is detailed by Roach et al. (2008), and Roach and Grimm (2011). Data and expertise garnered by stormwater monitoring near the outflow of the IBW helped pave the way for a more expansive stormwater research effort facilitated by a leveraged grant from the National Science Foundation (DEB-0918457, NSF Ecosystems, 2009-13). Through the Stormwater Nitrogen in Arizona (SNAZ) project, hierarchically nested urban stormwater catchments in Scottsdale, and another in Tempe, Arizona were instrumented with automated stormwater samplers (ISCO® 6700 automated pump samplers). A subset of those locations were fitted with bubbler modules (ISCO® 720 bubbler modules) for quantifying water height (and subsequently discharge), and tipping-bucket rain gauges (ISCO® 674). The study catchments differed in type of stormwater infrastructure, spanning a continuum from highly engineered stormwater infrastructure in older residential areas to non-engineered washes in the desert, but generally not in land-use type (land use in all study catchments is predominantly residential). Discrete stormwater samples were collected from most runoff-generating storms at the outflow of the study catchments from the fall of 2010 through the summer 2012. Rainfall samples were collected at a subset of the locations during several storms to provide data that would contribute to an assessment of sources of materials in runoff. Results of this study are detailed by Hale et al. (2014, 2015). Sampling at most locations ceased at the end of the SNAZ award period, but the CAP LTER continues its long-term monitoring of runoff at several locations along the IBW, as well as other locations in the greater Phoenix metropolitan area. Data from the CAP LTER's long-term stormwater monitoring program are available through the CAP LTER website and the Environmental Data Initiative data portal. - Grimm N.B., Arrowsmith J.R., Eisinger C., Heffernan J., MacLeod A., Lewis D.B., et al. (2004) Effects of urbanization on nutrient biogeochemistry of aridland streams. In: Geophysical Monograph Series. (Eds R.S. DeFries, G.P. Asner and R.A. Houghton), pp. 129–146. American Geophysical Union, Washington, D. C. - Grimm N.B., Sheibley R.W., Crenshaw C.L., Dahm C.N., Roach W.J. and Zeglin L.H. (2005) N retention and transformation in urban streams. Journal of the North American Benthological Society 24, 626–642. - Hale R.L., Turnbull L., Earl S., Grimm N., Riha K., Michalski G., et al. (2014) Sources and Transport of Nitrogen in Arid Urban Watersheds. Environmental Science & Technology 48, 6211–6219. - Hale R.L., Turnbull L., Earl S.R., Childers D.L. and Grimm N.B. (2015) Stormwater Infrastructure Controls Runoff and Dissolved Material Export from Arid Urban Watersheds. Ecosystems 18, 62–75. - Roach W.J. and Grimm N.B. (2011) Denitrification mitigates N flux through the stream–floodplain complex of a desert city. Ecological Applications 21, 2618–2636. - Roach W.J., Heffernan J.B., Grimm N.B., Arrowsmith J.R., Eisinger C. and Rychener T. (2008) Unintended consequences of urbanization for aquatic ecosystems: a case study from the arizona desert. BioScience 58, 715–727. - Walsh C.J., Roy A.H., Feminella J.W., Cottingham P.D., Groffman P.M. and Morgan II R.P. (2005) The urban stream syndrome: current knowledge and the search for a cure. Journal of the North American Benthological Society 24, 706–723.