DOI: 10.6073/pasta/2dd858c5b7e2eb1d397b8e2fb3b18165
title: Long-term monitoring of stormwater runoff and water quality in urbanized watersheds of the greater Phoenix metropolitan area, ongoing since 2008

description: Urbanization dramatically alters 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 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 major drainage in the greater Phoenix metropolitan area, draining much of the City of Scottsdale, and a tributary to the Salt River. A model of soft engineering, the IBW as it runs through 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 and as a floodplain. A unique biogeochemistry of this novel system is detailed by Roach et al. (2008), and Roach and Grimm (2011). Stormwater sampling is conducted near the outflow of the IBW ~0.6 km above its confluence with the Salt River. The sampling location coincides with a permanent USGS gauging station (USGS 09512162 INDIAN BEND WASH AT CURRY ROAD, TEMPE, AZ) that provides corresponding discharge data. Automated stormwater sampling equipment (ISCO® 6700 automated pump sampler) is used to collect discrete stormwater samples throughout the hydrograph of most runoff-generating storms. Data and expertise garnered by the 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, ten hierarchically nested urban stormwater catchments in Scottsdale and Tempe, AZ were instrumented with automated stormwater samplers (ISCO® 6700 automated pump samplers). A subset of those 11 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 ten 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 not in land-use type (land use in all study catchments is predominantly residential). As per sampling near the outflow of the IBW, discrete stormwater samples were collected from most runoff-generating storms at the outflow of the 10 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. (2014a, 2014b). Sampling at most locations ceased at the end of the SNAZ award period, but the CAP LTER continues its long-term monitoring of runoff near the outflow of the IBW. Four new sites that drain into the Salt River were added in the winter of 2016. Three of the new sites are located near downtown Phoenix in the Rio Salado habitat restoration area, and the fourth catching runoff from numerous freeways and entering the Salt River channel above the Tempe Town Lake. 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. (2014a) 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. (2014b) 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.