|Evaluation of Receiving Water Improvements from Stream Restoration (Accotink Creek, Fairfax City, VA) (EPA/600/R-08/110) September 2008
Installation of best management practices (BMPs) in watersheds or streams is widely used as a means of reducing, eliminating, or controlling the input of human-based physical, chemical, or hydrologic stressors to those systems. Although BMPs may be effective in managing a particular stressor, installation of stream bank and channel restoration alone may not fully restore nor fully protect the biological condition of the receiving waterbody since multiple stressors are known to affect aquatic biota.
The National Risk Management Research Laboratory (NRMRL), part of U.S. Environmental Protection Agency’s (U.S. EPA) Office of Research and Development (ORD) evaluated the effectiveness of stream bank and channel restoration as a means of improving in-stream water quality and biological habitat in Accotink Creek, Fairfax City, Virginia using discrete sampling and continuous monitoring techniques before and after stream restoration. Continuous water quality monitoring showed that temperature of the creek changed with season and wet weather flow events with the highest temperature observed in summer (e.g., July). Specific conductivity was higher in winter due to street salting while pH stayed close to neutral year around. There were no statistically significant differences in other chemical constituents and bacteriological indicator organisms before and after restoration as well as upstream and downstream of the restoration. Macroinvertebrate indices such as Virginia Stream Condition Index (VASCI) and Hilsenhoff Biotic Index (HBI) and Emphemeroptera, Plecoptera, Trichoptera (EPT) taxa showed a general improvement in biological quality between pre-and post-restoration. The differences were statistically significant for VASCI, HBI, and EPT taxa. However, they were all below the impairment level, indicating poor water quality conditions. The United States Geological Survey (USGS) also performed continuous monitoring and discrete sampling under an Interagency Agreement (IAG No. DW-14-922064010) to U.S. EPA. Their monitoring and predictive equations showed a stronger relationship between turbidity and suspended sediment concentration than turbidity and E. coli. There was no change in the results derived from the predictive equations before and after restoration, likely because improved conditions have yet to be realized or stream restoration did not reduce sediment transport. A pebble count analysis also suggested that very little has changed in the restoration reach.
These results indicate that stream restoration alone may have little effect on improving the conditions of in-stream water quality and biological habitat. It should be recognized that improvement may not be reflected in a two year post-restoration period and that additional monitoring is needed. Also, reduction of stormwater runoff volumes and associated pollutants of concern should be addressed in the watershed through source control and stormwater retrofits to achieve desired biological outcomes.
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