Moving toward more strategic approaches in stream restoration

Background/Question/Methods

Water quality in the Chesapeake Bay continues to decline despite major efforts made to restore it.  Major challenges include controlling the transport of excess of water, nutrients, and sediments from urbanized catchments to downstream waters.  Streams play a key role at controlling nitrogen and sediment export, but degradation of these ecosystems decreases their capacity to provide such an important ecological function.  Consequently, stream restoration efforts are booming in areas adjacent to large urban population centers with acute problems of nitrogen pollution and high sediment yield.  Despite the boom, the long- term success of stream restoration and support from society depend on effectiveness evaluations that improve linkages between restoration actions and changes that result in the delivery of specific goals.  In this study, we provide a quantitative assessment of the effectiveness of stream restoration at reducing loads of nitrogen and sediments transported from headwater streams to downstream waters in the MD Western Coastal Plain, and seek to determine if restoration success is associated with strategic targeting of restoration such as the position of stream in the watershed, and the restoration design. We assessed effectiveness of restored reaches by comparing TSS and N concentrations up and downstream of the restoration, and also by determining net export at the reach scale using a mass balance approach.

Results/Conclusions

Most of the restored streams monitored were ineffective at reducing fluxes of N and TSS.  Restoration design and position of stream in the watershed were important factors.  During average flow conditions, lowland channels that allowed the contact of streamflow with the vegetation along the riparian zone and floodplain reduced TSS and N fluxes significantly.  One of these streams has been converted to a wetland-stream complex, and was the only restoration that attenuated peak flows and reduced fluxes during stormflow conditions.  Dissolved inorganic was the dominant nitrogen form during lower flow conditions, while particulate was the dominant nitrogen form during high-flow periods.  Particulate N and TSS concentrations were highly correlated.  Hence, the capacity of the stream-wetland complex of reducing loads of pollutants in different forms and during different hydrological conditions improved the effectiveness of restoration substantially, and allowed the project to meet not only ecological but also societal needs for water quality and stormwater control.  This shows that it is possible to enhance restoration effectiveness by using more strategic approaches for the selection of sites and restoration designs.