The Impact of Stream Restoration on Macroinvertebrate Communities in an Urban Forested Watershed
Stream restoration can lead to improved habitat quality, increased macroinvertebrate abundance and diversity, and reduced concentrations of nutrients and contaminants. Macroinvertebrates are vital in connecting the food web and breaking down organic matter to provide energy for higher trophic levels. Not only are macroinvertebrates important for the function of stream ecosystems but they also serve as biotic indicators of stream health. Based on species presence and abundance practitioners can determine if the stream water quality is ‘poor’ or ‘excellent.’ To study the impact of stream restoration on macroinvertebrate communities, a multi-year project at Reedy Creek Reserve was designed. The Reedy Creek watershed is a 14 mi2 urban forested watershed located in a nature preserve. Within the headwaters of the watershed, 5 sub-watersheds were delineated based on the surrounding land-use influence of development (D2, D1), forested control with restoration (C1), forested control without restoration (C2), pond (P1), agricultural (A4, A3, A3, A1) and Reedy (R2, R1). Taxa richness, EPT richness, total abundance, the North Carolina Biotic Index (NCBI), and EPT biomass were measured to study the impact of stream restoration on macroinvertebrate communities. A Before-After-Control-Impact study design was used to determine if restoration had a significant impact on the study metrics. Data collection in this study included summer 2016 through summer 2020. Restoration began in December 2017 and was completed in February 2019. After restoration, abundance and NCBI values increased at all sub-watersheds. For the development sub-watershed, taxa richness was significantly different after restoration with averages increasing from 5-8 taxa and abundance was significantly different with averages increasing from 29 to 87 total organisms after restoration. For the agricultural sub-watershed, taxa richness was significantly different after restoration with averages decreasing from 10 to 8 taxa, EPT richness was significantly different after restoration with averages decreasing from 4 to 3 taxa, and the NCBI score was significantly different after restoration with the average NCBI score increasing from 5.55 to 6.98 reflecting a change in water quality from ‘good-far’ to ‘poor’ after restoration. For the forested control sub-watershed, there was no change in taxa richness (13 taxa), EPT richness (6 taxa), abundance (58 total organisms), and NCBI score (4.65/Good) after restoration. Changes in land-use led to different patterns among biotic metrics that are sensitive to environmental variation such as taxa richness, EPT richness, and NCBI. During the time frame of this study, even though patterns were observed there were very few statistically significant differences that were contributed to the fact that the restoration project is still new (2-3 years depending on the site). Practitioners suggest it can take upwards of 10 years for a stream to recover after restoration. To correctly assess the outcome of stream restoration projects, multiple years of pre-restoration and post-restoration data are needed.