Impacts of stream restoration on macroinvertebrate community structure and adult stream insect colonization on Big Spring Run, Lancaster County, PA

Because of the presence of a historic dam, Big Spring Run (BSR), located in Lancaster County, PA, and which serves as a tributary to the Conestoga River, has been severely impacted by legacy sediment.  By removing the legacy sediment, a section of BSR was restored with the objective of returning it to its natural floodplain.  The purpose of this study was to examine how stream modification affects larval macroinvertebrate community structure as well as the abundance and diversity of recolonizing adult stream insects found along the restored section.  Larval macroinvertebrates were collected late April-early May for twenty-four months pre-restoration and thirty-two months post-restoration using a BACI (Before/After/Control/Impact) sampling design to compare larval macroinvertebrate samples from three control sections to one restored section.  Adult insects were collected using one malaise trap per stream site and sampled post-restoration only.  Samples were identified to generic level in the lab for analysis.  A nonmetric multidimensional scaling (NMDS) analysis was performed to compare macroinvertebrate communities while adult insects were compared using the Simpsons Diversity Index.  After thirty-two months post-restoration, our results indicated no significant difference in the macroinvertebrate community structure in the restored section compared to the reference streams of previous post-restoration years.  Control and east branch reference streams initially showed greater abundance of adult EPT taxa in 2014 compared to the restored reach (Mainstem) and west sites. Early assessment of adult insect diversity does not appear to differ between the restored reach and all other sites.  Since results from stream restoration projects are not immediately observable and require post restoration monitoring, this project underscores the importance of long-term monitoring of larval macroinvertebrate communities as well as recolonizing adults to be able to determine if stream restoration provides sustainable improved habitat necessary to maximize stream biodiversity.