Abstract:
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.
