Does Restoration of Urban Riparian Zones Impact Stream Water Quality in Portland, Oregon

Riparian zones influence urban stream quality through factors such as shading the stream, adding nutrients through leaf litter, stabilizing the stream banks to reduce turbidity, and filtering toxins out of the water. Riparian restoration often involves changing plant assemblage to be more diverse and include primarily native species instead of non-native, improving connection to the stream through changing stream morphology, improving species habitat, and reducing pollution. The goal of this study was to determine if urban riparian restoration projects in the region were successful, and if not, why that may be the case. The study was performed in the Portland, Oregon region, with 36 sites, 12 restored urban, 12 unrestored urban, and 12 non-urban streams. At each site I measured riparian conditions as well as in-stream water quality variables (e.g., temperature, turbidity, conductivity, pH), velocity, and stream habitat conditions. The turbidity and conductivity models were not significant (p>0.05), and the trend in RSA data indicated that it did improve after restorations (restored median = 213.5, unrestored median = 198). The temperature was not improved in the restored streams, with the median temperature being higher in restored streams than unrestored streams (restored median = 20.5 °C, unrestored median = 18.85 °C ). The findings did not indicate that the restored urban streams experienced significantly improved water quality compared to the unrestored urban streams. The age of a restoration project may be a factor as to why those projects have not improved the water quality, however further research is needed.