Evaluating Macroinvertebrate Communities at the Nexus of Freestone and Limestone Streams

The Yellow Breeches, a tributary of the Susquehanna River, is a freestone stream flowing 49 miles through limestone-dominated valleys. The character of the stream changes as limestone streams join it at several points, altering the bedrock, formation and water source. Stream chemistry and macroinvertebrate communities consequently change in conjunction with the physical and chemical transformations. As cornerstones of the food chain and ecosystem, shifts in these populations can have widespread effects on the stream community as a whole. It is essential to determine factors promoting community changes to be able to accurately determine the conservation measures that can be safely taken without changing the overall ecosystem structure. Therefore, this project strives to assess whether there is significant difference between macroinvertebrate communities in the two streams as they join and if one exists, to identify the chemical and physical parameters contributing to that shift. To accomplish this, visual assessments, nutrient analysis, and macroinvertebrate sampling were performed at eleven sites within thirty meters of the mixing site. Preliminary data reveals significant difference in macroinvertebrate communities in the limestone and freestone influenced sites in some keystone species, as well as significant differences nearly all chemical parameters and only one physical parameter, substrate composition. Additional testing will be performed at this site as well as two additional sites to further specify the cause of the change in community structure and composition