Wetland, Stream Bank, and Shoreline Restoration
Benthic Habitat Restoration + Reference Relocation = B3 (Bring Back the Bugs)
How do we get that forested, healthy stream off the impaired waters list? Why aren’t there fish in our restored stream? The answer to both questions may bug you.
Benthic macroinvertebrates (benthos) include aquatic insects (e.g. mayflies, stoneflies, caddisflies, midges, beetles), snails, worms, mussels, clams and crayfish that live at least a portion of their lives in an aquatic environment. Different species can tolerate a wide range of conditions. Some survive in very poor aquatic environments (tolerant species), while others require excellent aquatic habitat (intolerant species). In addition to fish diversity and ambient (chemical) water quality sampling, throughout the Southeast benthos have long been used to document waterways’ use support ratings, including impairments (303(d) listings). They have also begun to be formally used to determine stream restoration success and, thereby, mitigation credit release.
Similar methods of habitat restoration and “bug seeding” (i.e. relocation of intolerant benthic populations from high quality reference reaches) was implemented at two locations, one in North Carolina’s Triangle Region (Northern Outer Piedmont) and one in South Carolina’s Up State (Southern Outer Piedmont).
The NC site was part of an Environmental Protection Agency-funded 319 watershed plan. The study area (Smith Creek) was added to the state’s 303(d) list, based solely on benthic results from one monitoring location, immediately upstream from the creek’s confluence with the Neuse River. Benthos was monitored at three sites for three years. During year two an additional six sites were sampled. Year two results indicated that many portions of the study area would be considered supporting, if evaluated separately. Additionally, one site, with a nearly excellent rating, was identified (reference reach). During the late fall/early winter of year two, habitat enhancement was completed at one site. During late winter/early spring of year three, populations from the reference reach were relocated to the enhanced site. While not resulting in significant increases in taxa richness, several highly intolerant species, which had not been found at the site during the previous two years’ sampling efforts, were identified following the year three sampling.
The SC site is a stream restoration along Greenville Branch, a tributary to Fairforest Creek, which flows through downtown Spartanburg, SC. Its construction was completed in December 2017 and provides permittee-responsible mitigation to offset unavoidable stream impacts associated with the Spartanburg Downtown Memorial Airport’s runway expansion. Restoration activities included “daylighting” approximately 1,125 lf of closed drainage system and restoring an additional 710 lf of channel.
The project has improved bank stability, provided water quality improvements, and improved in-stream and riparian habitat. Because of unavoidable utility, transportation, stormwater and other project constraints, the upstream-most reach includes an integrated series of cascade/pools. The downstream reaches utilize more traditional boulder and log grade control structures, natural meander patterns, and aquatic habitat enhancements.
As a result of extended permit negotiations with the US Army Corps of Engineers’ Charleston District, the project is required to document/demonstrate its functional uplift by meeting both numeric ambient water quality, as well as numeric benthic macroinvertebrate performance metrics during its five-year monitoring period. The Greenville Branch site is the first mitigation project in the Southeast to be held to such standards. In order to fulfil this requirement, an innovative habitat enhancement and reference reach benthic relocation effort has begun to be implemented.
Both projects have demonstrated significant increases in benthic diversity after one year, compared to baseline (pre-restoration) conditions. While not yet statistically significant, similar monitoring results at both sites indicate that larger-scale implementation of these methods has the potential to facilitate watershed-wide functional uplift, which could result in impairment delisting.