Evaluation of Ecological Function in Restored Urban Streams

摘要

Stream restoration projects often result from compensatory mitigation and are designed to reestablish ecological function to degraded systems. However, these projects are rarely subjected to post-restoration evaluation. The overall goal of this study was to evaluate the effect of stream restoration on ecological function in urban low and mid-order streams in Greensboro, NC. We conducted monitoring at two restoration sites and three urban reference sites from November 2002 to December 2003. We also conducted (sup 15)N tracer enrichment experiments in a forested reference site, a restored urban site, and an unrestored urban site in August Sepetember 2004. Surface and hyporheic water for dissolved oxygen and surface water were sampled at monitoring sites for nutrients (NO(sub 3)(sup -), PO(sub 4)(sup -3), NH(sub 4)(sup +)). Benthic macroinvertebrates were collected both quantitatively and qualitatively and were used in metric analyses. Dissolved oxygen was significantly higher in surface and hyporheic water in restored compared to reference monitoring sites, and was significantly lower upstream and higher downstream of restored sites. NO(sub 3)(sup -) was significantly lower within restored sites. PO(sub 4)(sup -3) and NH(sub 4)(sup +) levels were not different between sites. NCBI water quality scores in all sites were Fair. Taxa richness was similar at restored and unrestored sites. These monitoring results indicate that restoration may be improving urban stream water quality and macroinvertebrate communities through improved habitat. Reduced NO(sub 3)(sup -) is especially important to basin-wide efforts to reduce N-loadings to downstream receiving waters. (Sup 15)N tracer experiments also indicated higher N-retention in a 2nd order restored reach compared to an unrestored reach. (Sup 15)N enrichment experiments showed that NH(sub 4)(sup +) uptake/m(sup 2) to periphyton was greatest in Talbots Branch, a relatively pristine forested stream, likely reflecting that the urban stream reaches have high concentrations of DIN, thus demand for NH(sub 4)(sup +) should be lower in those streams. However, restored Starmount GC had similar NH(sub 4)(sup +) vertical mass transfer velocity and higher rate of NH(sub 4)(sup +) uptake per m(sup 2) compared to unrestored OHenry despite greater stream depth and higher ambient NH(sub 4)(sup +) concentrations. This higher demand for NH(sub 4)(sup +) also suggests that restoration is having a positive effect on retention of N.