Phytoplankton composition within the tidal freshwater-oligohaline regions of the Rappahannock and Pamunkey Rivers in Virginia

摘要

The Rappahannock River is a major river system across north central Virginia prior to entering the Chesapeake Bay. In contrast, the Pamunkey River is smaller in size and joins the Mattoponi River to form the York River, which flows parallel to the Rappahannock before it also flows into Chesapeake Bay. A unique mixing area for both flora and environmental conditions exists in the tidal freshwater-oligohaline region of both rivers. This is a dynamic mixing section where freshwater and estuarine species are subject to the interaction of river flow and daily tidal rhythms. The phytoplankton composition in this region of the two rivers was identified over a 13.5-year period (July 1986-December 1999). The results indicated freshwater and estuarine populations forming a diverse assemblage of 268 taxa, with diatoms, chlorophytes, and cyanoprokaryotes the dominant flora. Phytoplankton in this region were predominantly freshwater taxa (e.g., >70%), with a diverse diatom assemblage representing >90% of the estuarine flora at these sites.