REVEALING THE HIDDEN PAST OF LEGACY SEDIMENTS FROM MIDDLE CREEK LAKE, SELINSGROVE, PA

Erosion of legacy sediments from Middle Creek Lake, south of Selinsgrove, PA, contribute to pollution in the Chesapeake Bay. A grist mill dam was built on Middle Creek in the late 1800’s, a small hydroelectric dam (Musser Dam) was installed in the same location in 1906, and after being destroyed by a storm in 1934, a larger, wooden dam operated from 1936 to 1992, when it was removed. We examine the deposition of legacy sediments that accumulated behind the dams and estimate the volume of sediment at the site. This sediment tends to easily erode following major rainstorms and is transported to the Susquehanna River, where it is deposited in the Chesapeake Bay. Here, it can smother benthic communitities and the nutrients can trigger deadly algal blooms. Over 30 sediment cores were drilled into the former lake bed using a telescoping auger, and the exposed banks of the modern creek were examined. The sediment can be subdivided into three categories: silty loam (youngest), clayey loam, and fluvial sediments (oldest). Based on the fine sediments and diatom communities containing Gyrosigma acuminatum, Pinnularia viridis, and Ulnaria ulna, the silty and clayey loams represent a lake environment, while the coarser, pre-dam deposits containing abundant Cocconeis placentula represent an active stream environment. Due to differential erosion of the underlying Trimmers Rock Formation (Devonian), these sediment layers are not present at every location. Bedrock strongly controlled sediment deposition until as late as 1938, based on aerial photos of the region. Once the bedrock was covered by sediment, the silty and clayey loams were prominent in all areas of the lake. Due to abundant sediment deposition near the inflow source, the location of Middle Creek has been altered. The PA Fish and Boat Commission originally estimated a total sediment volume of 760,000m³ for 100 - 178 acres. This study calculated a legacy sediment volume of 436,000m³ over an area of 119 acres. The total estimated volume of sediment in the lake basin was calculated to be 789,000m³. Based on this study, the lake was shallowing due to the amount of sediment infilling the lake basin; this meritted the deconstruction of the dam in 1992 by the PA Fish and Boat Commision.