The Efficacy of urban stream restorations to improve water quality across a spectrum of design approaches




Browning, Maura

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The most recent national water quality inventory lists more than one-third of assessed rivers in the United States as impaired or polluted (EPA 2002). Concerns over the impacts of urbanization – the second largest contributor of non-point source pollution to surface water (Veissman and Hammer 2005) – have resulted in the initiation of major investments in urban stream restoration in the United States. However, less than 10% of stream restorations are currently post-monitored for goal attainment (Bernhardt et al. 2005; Hassett 2007). This study strives to address the wide research gap in post-stream restoration monitoring; particularly those associated with urban, headwater streams, as they receive the largest share of river restoration dollars and effort in the United States (Bernhardt and Palmer 2007). More specifically, this study focuses on water quality monitoring, nationally one of the most commonly stated project goals of stream restoration (Bernhardt et al. 2005). The general research design involved water quality and discharge monitoring of three restored stream reaches across a spectrum of design approaches (“hard” structural design, “soft” bioengineering design, and “seepage wetland” design) on a bimonthly basis between October 2007 and April 2008, primarily during baseflow conditions. Upstream and downstream water quality data for nitrogen (nitrate + nitrite and ammonium), total suspended solids, pH, dissolved oxygen, temperature, and specific conductivity were statistically evaluated with paired t-tests. Water quality improvement amongst the three design approaches was statistically evaluated by comparing the differences between upstream and downstream concentrations using an ANOVA test. All statistical analyses utilized a 95% confidence level and were conducted using SPSS statistical software. The efficacy of the three design approaches was further evaluated by calculating percent differences between upstream and downstream concentrations as well as by calculating nitrogen and sediment removal efficiencies. This study’s results suggests that (1) all restored urban streams have the potential to improve water quality, as demonstrated by statistically significant differences between upstream and downstream concentrations for nitrate-N and dissolved oxygen in all three streams in the paired t-tests; and (2) the “seepage wetland” approach exhibited a greater percent removal of nitrate-N than the other two approaches.



Stream, Restoration, Urban, Water, Quality