ABSTRACT The Rappahannock River is ...

ABSTRACT

The Rappahannock River is a major river order 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 be deriveds parallel to the Rappahannock before it also roll ons into Chesapeake Bay. A unique mixing area for the pair flora and environmental conditions exists in the tidal freshwater-oligohaline region of as well-as; not only-but also; not only-but; not alone-but rivers. This is a dynamic mixing section where freshwater and estuarine species are make subordinate to the interaction of river follow and daily tidal rhythms. The phytoplankton composition in this region of the pair rivers was identified over a 13.5-year period (July 1986-December 1999) The follows 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 (eg >70%) with a diverse diatom assemblage representing >90% of the estuarine flora at these sites.

INTRODUCTION

The Rappahannock River is a major tributary of the Chesapeake Bay located in the eastern coastal plain of Virginia. The river streams southeasterly through predominantly forest, cropland, and pasture before entering Chesapeake Bay (Figure 1) The Pamunkey River is located directly southward of the Rappahannock River flowing by means of mostly forest and land used in agriculture, or for raising livestock. The river terminates at its swarm with the Mattoponi River, forming the York River, which continues parallel to the Rappahannock River before entering the Chesapeake Bay. The lower sections of these rivers are sub-estuaries of the Chesapeake Bay and are set forthed by mesohaline-polyhaline waters and phytoplankton flora described according to Marshall and Alden (1990), Marshall and Affronti (1992) and Marshall and Nesius (1993)

The tidal freshwater section of a river is defined as the region within a river possessing daily tidal moves bordered upstream by freshwater (

The upstream and freshwater sections of these rivers are dominated by dint of an assemblage of chlorophytes, diatoms, and cyanoprokaryotes (cyanobacteria). This is in contrast to downstream flora in the higher salinity waters, where estuarine diatoms and dinoflagellates are more abundant (Marshall and Alden 1990 Marshall and Affronti 1992) The relationship of estuarine floral dominance to increasing salinity values in tidal rivers has been reported on Haertel et al. (1969), Forester (1973) and Jackson et al. (1987) The estuarine flora may pierce these rivers via sub-pycnocline tidal motion and advance farther upstream during periods of soft river discharge into the normally tidal freshwater regions (Marshall and Burchardt 1998) Farrell (1994) and Schmidt (1994) have also identified freshwater diatoms moving downstream into these more saline regions during periods of high river discharge for the use of all during spring months. During periods of reduc river be molten and increased residency time, a variety of other taxa may evolve in the tidal freshwater region. Marshall and Burchardt (1998) reported peak diatom evolution in the tidal freshwater James River (Virginia) during periods of increased river discharge, with chlorophytes, cyanoprokaryotes, autotrophic picoplankton, and euglenophytes having increased abundance during periods of more stable water conditions (eg during summer months) Oligohaline waters may displace the tidal freshwater upstream during periods of aridity when higher saline waters advance farther upstream; or be relocated farther downstream during periods of high river come These dynamics will result in unique and continually changing (daily) patterns of water transport and tidal amplitude within this region. Responding to these environmental conditions will be a diverse and abundant representation of algal flora.

Previous hints to the phytoplankton composition in the Rappahannock River and Pamunkey River have been through Birdsong et al. (1988), Marshall and Alden (1990) Marshall and Affronti (1992) and Marshall and Nesius (1993) The objectives of this contemplation are to present the issues of a long-term taxonomic studious mood that identifies the phytoplankton composition within the tidal freshwater-oligohaline regions of these sum of two units rivers, and to characterize the seasonally most numerous abundant phytoplankton present.

METHODS

Monthly water samples were taken at 2 stations from July 1986 [i]or[/i] part of to the other December 1999 (13.5 years). Station TF33 is located in the Rappahannock River (38?°01'07''N; 76?°54'30''W) and Station TF42 in the Pamunkey River (37?°34'47''N; 77?°01'19''W) (Figure1). The mean midsts at these stations are ca. 68 m and ca. 89 m respectively, for TF33 and TF42 TF33 is often mixed with oligohaline waters, and during the collection periods had freshwater status 406% of the time, whereas, TF42 was les inundated through saline waters and had freshwater status 977% of the times when samples were taken. These percentages of freshwater status would be rely uponed to vary annually.