Vertebrate Community Trajectory in Regenerative Stream Conveyance (RSC) Restoration

Mark Southerland, PhD, Senior Ecologist, Tetra Tech

This study assessed the trade-offs inherent in stream restorations using the Regenerative Stream Conveyance (RSC) or restored stream-wetland technique. Specifically, it quantifies the aquatic vertebrate community trajectories that should be expected from RSC restorations implemented in lowland Coastal Plain streams with nutrient-rich waters. We defined the reference conditions (minimally-disturbed) for Coastal Plain aquatic vertebrate communities in both single-thread streams and stream-wetland complexes, using a literature review and data from Maryland Biological Stream Survey (MBSS). We sampled and analyzed the aquatic vertebrate communities (fish and herpetofauna) in 11 streams that have been converted to RSCs, along with 24 comparable references of three types. In general, RSC fish communities were more similar to low-quality single streams than to high-quality single streams or stream wetland complexes. Specifically, fish diversity in RSCs was lower than in high-quality sites and decreased with higher conductivity and lower dissolved oxygen. Sensitive fish species found in high-quality references (e.g., creek chubsucker, fallfish, madtoms, lampreys) were absent from RSCs and low-quality sites. Fish indices of biotic integrity (IBIs) were also lower in RSCs than in high-quality sites, but may be higher than in low-quality sites. While RSCs recreated the physical conditions typical of high-order stream wetland complexes in low-order reaches, they did not attain the levels of dissolved oxygen, conductivity, and flow found in high-quality sites. Herpetofauna diversity showed few patterns, expect for higher frog abundance in RSCs than references. Overall, vertebrate uplift in RSCs appears to be constrained by continuing poor water quality. Variability among the 11 RSCs likely resulted from differences in water quality, canopy shading and temperature, stream width and depth, as well as restoration design and landscape setting. These results should help practitioners and regulators develop realistic expectations of biotic resource changes that occur when defined-channel stream systems are transformed into less-defined stream wetland complexes in urban-suburban settings.

Author Bio

Mark Southerland has a Ph.D. in ecology and has spent the last 30 years working as a consultant to monitor, assess, and restore ecosystems in the Chesapeake Bay watershed. He was the primary author of the EPA national program guidance on biological criteria and has been the lead consultant on the Maryland Biological Stream Survey for the Maryland Department of Natural Resources (DNR) since its inception in 1993. He has also supported the impaired waters, stressor identification, and TMDL programs for the Maryland Department of the Environment (MDE). Since 1996, he has helped 16 counties and cities in Maryland, Virginia, Delaware, and South Carolina develop stormwater programs and comply with the Chesapeake Bay and local TMDLs. Mark was previously chair of the Maryland Water Monitoring Council Board and Howard County Environmental Sustainability Board. He is also a member of the Science Council of the Maryland Academy of Sciences, Safe Skies Maryland, and Patapsco Heritage Greenway.