Preliminary Report On Diatom Communities in the Upper Main Stem of the Susquehanna River in 2013-2014

Elaine Langone Center, Terrace Room

The upper main stem of the Susquehanna River is formed by the confluence of the West and North Branches, each of which is chemically and physically distinctive. The upper main stem retains the signatures of the two branches due to weak lateral mixing, and we refer to them as the North Branch plume (NBP) and West Branch plume (WBP). Thus, characterization of the diatom communities required samples taken from sites that occur in the plumes of both branches. We sampled sites at a transect that straddles Byers Island near Shamokin Dam, PA and below the Adam T. Bower inflatable dam at Sunbury, PA. Samples were taken in the summer and fall of 2013 and the summer of 2014 and prepared for examination by light and electron microscopy. Within the plumes of the two branches, we identified four particular habitats inhabited by diatom communities: sediment, stone, plant and plankton. We eliminated epiphytes from this analysis because beds of submerged and emergent plants occurred only in WBP. Samples from WBP had 36, 28 and 4 species in the stone, sediment and plankton communities, respectively. Similar samples from NBP had 22 (stone), 51 (sediment) and 5 (plankton) species. Of the diatom communities on stone surfaces, there were only 9 species in common to NBP and WBP. Similarly, sediment samples from both plumes had only 11 species in common. No diatom species were common to the plankton of both plumes. Habitats of the NBP were dominated by small centric species (e.g. Stephanodiscus parvus, Cyclotella atomus, Stephanocyclus meneghiniana, and Discostella pseudostelligera), all taxa that were absent from the WBP.