Tidal Freshwater and Oligohaline Aquatic Beds
The hydromorphic herbaceous vegetation of this ecological group is restricted to small guts, shallow tributary creeks, and large marsh pools along freshwater and oligohaline sections of tidal rivers. Mean water depths of these habitats are too great for emergent aquatics. Communities of this group are known from Maryland south to South Carolina. In Virginia, they are best documented in the extreme southeastern part of the state, along the wind-tidal Northwest and North Landing Rivers and tributaries of Back Bay. Similar habitats and vegetation also appear to be present in freshwater, lunar-tidal guts of the upper Pamunkey and Mattaponi Rivers (tributaries of the York River) and the Chickahominy River (tributary of the James River). Habitats may be subject to water level fluctuations > 1 m (3 ft) and to regular or intermittent exposure at extreme low tides. Vegetation consists entirely of floating and submerged aquatics. Common hornwort (Ceratophyllum demersum) is the most important and abundant species. Bladderworts (Utricularia spp.), western waterweed (Elodea nuttallii), greater duckweed (Spirodela polyrrhiza), and sword bogmat (Wolffiella gladiata) are associates. The southeastern Virginia habitats with water < 60 cm (24 in) deep have sparse to dense surface covers of white water-lily (Nymphaea odorata ssp. odorata) or, at one site, American lotus (Nelumbo lutea). On the Chickahominy River, narrow-leaved spatterdock (Nuphar sagittifolia) forms large, floating mats.
The dynamics of tidal, aquatic communities dominated by vascular plants are complex and poorly understood. The distribution and abundance of vascular plants in these habitats are probably controlled by responses to water chemistry, water clarity and light penetration, the impact of currents and boat wakes, and herbivory by aquatic animals. Freshwater and oligohaline aquatic beds are important breeding and foraging sites for many insects, numerous crustaceans, and some fish. The naturalized introductions hydrilla (Hydrilla verticillata) and Eurasian water-milfoil (Myriophyllum spicatum) are rampant invaders of shallow, freshwater aquatic habitats in eastern Virginia. Because both species readily outcompete native aquatic plants, they poses serious threats to the integrity of freshwater aquatic communities.
Reference: Coulling (2002), Fleming and Moorhead (1998), Moore et al . (2000).
Click on the images below to open a larger image in a separate window.Large aquatic bed along a tributary of the wind-tidal Northwest River in the City of Chesapeake. White water-lily (Nymphaea odorata ssp. odorata , floating), common hornwort (Ceratophyllum demersum), and common bladderwort (Utricularia macrorhiza) are the most abundant species here. Photo: William H. Moorhead III / © DCR Natural Heritage.
Floating mats of narrow-leaved spatterdock (Nuphar sagittifolia) on the Chickahominy River near the mouth of Diascund Creek, New Kent County. Photo: Chris Clampitt / © DCR Natural Heritage.
This group is poorly represented by existing quantitative data. The Common Hornwort type is supported by only two plots from the same site, while the Tapegrass type is supported by only one plot.The Narrow-Leaved Common Spatterdock community is based on qualitative information only from the Chickahominy River, to which it appears to be restricted in Virginia, and the White Water-Lily type is based on observation data from several watersheds. Other, compositionally distinct floating aquatic bed communities may be present in southeastern Virginia and may warrant recognition as community types if additional examples can be documented. Moore et al. (2000) recognized several other communities in the greater Chesapeake Bay estuary, but this classification has not been fully incorporated into the USNVC. Further inventory of this group is clearly needed, although it is limited by accessibility of sites and the taxonomic skills of surveyors. Click on any highlighted CEGL code below to view the global USNVC description provided by NatureServe Explorer.