Relationship Between Discharge and %Ept in the Upper Main Stem of the Susquehanna River During the Summer Months of 2016 Through 2018

In this study, we are continuing the tenth year in a long-term study of benthic macroinvertebrate communities (BMI) in the upper main stem of the Susquehanna River from mid-summer collections. The benthic communities provide an assessment of both water quality and habitat variation between different temporal and spatial zones of the same river. As evaluation tools, BMI are useful in studying long-term trends because their life histories can span months to years. The study sites are on a transect that straddles Byers Island near the Sunbury Generation LP and below the Adam T. Bower inflatable dam at Sunbury, PA. The four sample locations are within the plume from the West Branch (site 1) and plume of the North Branch (sites 2-4). We follow the EPA guidelines for passive sampling in non-wadeable streams with the use of rock baskets, which emphasize drifting and colonizing animals. Riverine discharge is variable, but can reflect stochastic seasonal trends. The general weather patterns for the summers of 2016-2018 ranged from almost drought conditions in 2016 to the very wet summer of 2018. Discharge averaged from May through July relative to the 80-year average for those months was 48% (2016), 98% (2017), and 174% (2018). The %EPT (Ephemeroptera, Plecoptera, Trichoptera) values from the rock basket samples rose from 59.25% (2016), to 75.75% (2017) to 82.5% (2018). Indeed, discounting site 4, which is somewhat problematic as a site, the average for 2018 would rise to 93%. The association of EPT taxa with discharge seems to be related in the upper main stem. Ignoring site 4, the relationship between discharge and %EPT for the three years has an R2 of 0.67