Macroinvertebrate Assemblage Survey of Sandy Creek in Durham County, NC: Current Status, Pre-Restoration, and Post-Restoration Comparisons

Abstract

Stream and wetland restoration has become a widely used intervention for combatting the negative effects of urban stream syndrome and the water quality detriments that accompany it. Urban stream syndrome often occurs in watersheds with high impervious surface land cover and can lead to degradation of water quality, streambank instability, streambed incision, and disrupted sediment transport. All of these effects culminate in the loss of plant and animal biodiversity. Restoration projects such as the one being researched here aim to combat these issues. Macroinvertebrates have been used as a proxy for water quality and to compare streams of different quality. They serve as a tool for investigating the success of a restoration project on improving biodiversity and ecosystem function. This study aims to contribute to long-term monitoring of restored streams at the Duke University Wetland Center’s Stream and Wetland Assessment Management Park (SWAMP) as well as draw temporal conclusions about the success of the restoration efforts. SWAMP is composed of restored areas of stream, riparian wetlands, constructed wetlands, and retention ponds to better treat runoff into Sandy Creek in Durham County, NC. This system’s drainage area is dominated by upstream urban development leading to poor water quality and extreme erosion and incision, typical of streams experiencing urban stream syndrome in the Piedmont of North Carolina. A variety of ecological indexes and parameters were measured using kick-net, D-net, and leaf litter pack collection methods conducted in the spring and fall of 2022. Results indicate an overall improvement in North Carolina Biotic Index (NCBI) in all sites over time with the current NCBI of SWAMP being similar to that of the reference reach Mud Creek (MC). Comparing sites before restoration in 2001 to 2023 shows that the NCBI has improved for WT1, a restored site, by nearly 30% and improved since 2008 by approximately 12%. Since 2008 MC, the reference site, has improved by approximately 17%. NCBI improvements at both sites could indicate outside factors such as water quality protection policies/practices curbing pollution in addition to the improvements resulting from the restoration have enhanced water quality. Water quality parameters investigated largely improved following restoration of WT1, with subsequent improvement in NCBI, while no notable changes occurred in MC. Both magnitude and variability of total phosphorus and total suspended solids decreased dramatically following the 2012-2013 restoration upstream of WT1. Other parameters investigated were Shannon Diversity Index and EPT percentage. There seems to be important improvements in macroinvertebrate assemblages because of the restoration although they do not seem to be fully conclusive of the restoration being the sole reason for macroinvertebrate assemblage improvement/recovery. This study contributes to the long-term records of SWAMP macroinvertebrate assemblages, allowing for comparisons of recovery over time. The results also highlight the link between macroinvertebrate populations and water quality improvements resulting from the restoration. This restoration project and others like it aim to return degraded streams to a near-natural state and improve the water quality and ecosystem function within them. The results of this study indicate trends toward the recovery of ecosystem functions though there are other factors outside of the scope of this study that could be contributing to the changes over time.