Persistent Urban Influence on Surface Water Quality via Impacted Groundwater

Abstract

Growing urban environments stress hydrologic systems and impact downstream water quality. We examined a third-order catchment that transitions from an undisturbed mountain environment into urban Salt Lake City, Utah. We performed synoptic surveys during a range of seasonal baseflow conditions and utilized multiple lines of evidence to identify mechanisms by which urbanization impacts water quality. Surface water chemistry did not change appreciably until several kilometers into the urban environment, where concentrations of solutes such as chloride and nitrate increase quickly in a gaining reach. Groundwater springs discharging in this gaining system demonstrate the role of contaminated baseflow from an aquifer in driving stream chemistry. Hydrometric and hydrochemical observations were used to estimate that the aquifer contains approximately 18% water sourced from the urban area. The carbon and nitrogen dynamics indicated the urban aquifer also serves as a biogeochemical reactor. The evidence of surface water-groundwater exchange on a spatial scale of kilometers and time scale of months to years suggests a need to evolve the hydrologic model of anthropogenic impacts to urban water quality to include exchange with the subsurface. This has implications on the space and time scales of water quality mitigation efforts.

Spatiotemporal Variability in Water Sources Controls Chemical and Physical Properties of a Semi‐arid Urban River System

“…Elevated tributary inputs in spring consisting of comparatively lower nutrient concentrations (<3 mg/L N; Gabor et al. ) helped to mitigate high nutrient loads from effluent through dilution, as seen in other studies. These tributary inputs include an important fraction of water from groundwater springs with concentrations of Cl − and NO 3 − indicative of urban impacts (Gabor et al.…”

“…Water in canals was presumably warmer due to absorption of high inputs of solar radiation into low volume drainage systems, while water temperature of tributaries in summer also is roughly 20°C (Gabor et al. ; USGS ).…”

“…; Gabor et al. ) and a water isotopes database (Bowen , accessed August 15, 2017). We averaged reported values for groundwater wells within 1 km of the river within each segment, resulting in one set of groundwater isotope values per segment.…”

“…; Gabor et al. ). Moreover, the relative proportion of flow from “natural” water sources may decline in the future as “engineered” inputs (wastewater effluent, untreated canal inflows) increase in response to growing populations and greater volumes of water diverted for human consumption.…”

Isotopic reconnaissance of urban water supply system dynamics

“…Stable isotopes in water are natural and conservative tracers documenting provenance information and have been used extensively in climatological (Rozanski et al, 1992;Gat, 1995;von Grafenstein et al, 1999;Aggarwal et al, 2005;Dutton et al, 2005), ecological (Hobson, 85 1999;Hobson et al, 1999;Bowen et al, 2005a;Wassenaar et al, 2009), ecohydrological (Dawson and Ehleringer, 1991;Jasechko et al, 2013;Evaristo et al, 2015;Evaristo and McDonnell, 2017;Matheny et al, 2017) , forensic (Bowen et al, 2005a;Bowen et al, 2005b;Bowen et al, 2007;Kennedy et al, 2011;Landwehr et al, 2014;Ueda and Bell, 2017), and hydrological studies (McDonnell et al, 1991;Klaus and McDonnell, 2013;Good et al, 2014;90 Gorski et al, 2015;Jefferson et al, 2015;Gabor et al, 2017;Jameel et al, 2018). Within the terrestrial hydrological cycle, significant isotopic differences between water sources (i.e., river, Hydrol.…”