Freshwater intertidal mudflats are characterized by low-growing rosette-leaved aquatics that are adapted to the tides that flush the community daily. At low tide, the community and rosette-leaved plants are exposed. At high tide, they are completely submerged in three to four feet of water.
This community is restricted to the freshwater portion of tidal rivers. All occurrences are on the Hudson River with about 90% in Greene, Columbia, and Dutchess Counties. There are estimated to be less than 100 occurrences in the state. Several of these occurrences are threatened because of shoreline development, invasive plants, and river channel dredging.
The number of freshwater intertidal mudflats in New York have probably remained stable in recent decades as a result of wetland protection regulations.
The number of freshwater intertidal mudflats in New York have probably substantially declined (about 80%) from historical numbers likely correlated with shoreline development and river channel dredging.
The main threats to this community are shoreline development (including railroad tracks), and invasion of exotic species, such as water chestnut (Trapa natans). Recreational boat traffic that scrapes across the mudflats at high tides, and ATV and motorcycle use at low tide cause direct degradation. Dredging of shipping lanes may also pose a threat by reducing water quality and altering natural tidal regime and sediment deposition.
Maintain tidal regime in marshes cut off from the Hudson River near the railroad tracks.
Buffers that diminish or eliminate disturbances in this estuarine community are critical considerations for any development project. Such disturbances include the influx of water-borne solutes (road salt, fertilizers, herbicides, pesticides, sewage), water-borne sediments, and noise pollution. Strive to minimize or eliminate hardened shorelines and maintain very low-sloped shorelines within the tidal zone. Maintain high connectivity between the river and the mudflat to encourage full tidal flushing during each cycle of the tides. For example, barriers such as railway causeways should have numerous culverts to allow sufficient hydrologic connectivity.
Survey areas adjacent to known freshwater tidal marshes and freshwater subtidal aquatic beds for more examples of intertidal mudflats. Search for additional sites on Long Island.
Collect sufficient plot data to describe variants based on topgraphic setting (e.g., large flats in open river, enclosed basins, adjacent to islands, along freshwater tidal creeks, etc.).
This community is currently restricted to the central Hudson Valley portion of the Hudson River, ranging from Albany to Poughkeepsie, with most examples occurring in Columbia and Greene Counties. Small examples of freshwater intertidal mudflats may also occur along tidal rivers on Long Island.
Freshwater intertidal mudflats occur along tidal rivers from New York to North Carolina.
A sparsely vegetated community characterized by low-growing rosette-leaved aquatics. This community occurs on exposed intertidal mudflats where the water is fresh, with salinity values below 0.5 parts per thousand (ppt). This community is best developed where mudflats are nearly level so that broad expanses are exposed at low tide. The plants are completely submerged in 0.9 to 1.2 m (3-4 feet) of water at high tide, and they are usually coated with mud.
Sparsely vegetated mudflats along tidal rivers that are exposed at low tide.
Known examples of this community have been found at elevations between -1 feet and 20 feet.
Freshwater intertidal mudflats are best observed at low tide. The characteristic rosette-leaved plants of this community are generally at their peak from mid-July through August.
This New York natural community encompasses all or part of the concept of the following International Vegetation Classification (IVC) natural community associations. These are often described at finer resolution than New York's natural communities. The IVC is developed and maintained by NatureServe.
This New York natural community falls into the following ecological system(s). Ecological systems are often described at a coarser resolution than New York's natural communities and tend to represent clusters of associations found in similar environments. The ecological systems project is developed and maintained by NatureServe.
Heteranthera reniformis (mud-plantain)
Orontium aquaticum (golden-club)
Sagittaria montevidensis ssp. spongiosa (spongy-leaved arrowhead)
Sagittaria rigida (sessile-fruited arrowhead)
Sagittaria subulata (awl-leaved arrowhead)
This figure helps visualize the structure and "look" or "feel" of a typical Freshwater Intertidal Mudflats. Each bar represents the amount of "coverage" for all the species growing at that height. Because layers overlap (shrubs may grow under trees, for example), the shaded regions can add up to more than 100%.
DeVries, C. and C.B. DeWitt. 1986. Freshwater tidal wetlands community description and relation of plant distribution to elevation and substrate. In: Polgar Fellowship Reports of the Hudson River National Estuarine Sanctuary Program 1986. E.A. Blair and J.C. Cooper, editors. Hudson River Foundation, New York, New York.
Edinger, G. J., D. J. Evans, S. Gebauer, T. G. Howard, D. M. Hunt, and A. M. Olivero (editors). 2014. Ecological Communities of New York State. Second Edition. A revised and expanded edition of Carol Reschke’s Ecological Communities of New York State. New York Natural Heritage Program, New York State Department of Environmental Conservation, Albany, NY. https://www.nynhp.org/ecological-communities/
Edinger, Gregory J., D.J. Evans, Shane Gebauer, Timothy G. Howard, David M. Hunt, and Adele M. Olivero (editors). 2002. Ecological Communities of New York State. Second Edition. A revised and expanded edition of Carol Reschke's Ecological Communities of New York State. (Draft for review). New York Natural Heritage Program, New York State Department of Environmental Conservation. Albany, NY. 136 pp.
Findlay, S.E.G., E. Kiviat, W.C. Nieder, and E.A. Blair. 2002. Functional assessment of a reference wetland set as a tool for science, management and restoration. Aquat. Sci. 64:107-117.
Kiviat, E. 1974. A fresh-water tidal marsh on the Hudson, Tivoli North Bay. Paper 14, In Third Symposium on Hudson River Ecology, Hudson River Environmental Society, Bronx, New York.
Kiviat, E. 1979. Hudson River Estuary shore zone: ecology and management. MA Thesis, State University College, New Paltz, New York.
Kiviat, E. and E. Beecher. 1991. Vegetation in the fresh-tidal habitats of Tivoli Bays, Hudson River. Hudsonia Ltd., Bard College Field Station, Annandale, New York.
Kiviat, Erik and Gretchen Stevens. 2001. Biodiversity assessment manual for the Hudson River Estuary Corridor. New York State Department of Environmental Conservation. Albany, NY.
Metzler, K. and R. Rosza. 1982. Vegetation of fresh and brackish tidal marshes in Connecticut. Newsletter of the Connecticut Botanical Society 10(1): 1-3.
Muenscher, W.C. 1937. VII. Aquatic vegetation of the Lower Hudson area. 1936. Biological Survey. 11:231-248.
New York Natural Heritage Program. 2023. New York Natural Heritage Program Databases. Albany, NY.
Odum, W.E., T.J. Smith III, J.K. Hoover, and C.C McIvor. 1984. The ecology of tidal freshwater marshes of the United States east coast: A community profile. U.S. Fish and Wildlife Service, Washington, D.C. FWS/OBS-83/17.
Reschke, Carol. 1990. Ecological communities of New York State. New York Natural Heritage Program, New York State Department of Environmental Conservation. Latham, NY. 96 pp. plus xi.
This guide was authored by: Timothy G. Howard
Information for this guide was last updated on: March 6, 2017
Please cite this page as:
New York Natural Heritage Program. 2023. Online Conservation Guide for Freshwater intertidal mudflats. Available from: https://guides.nynhp.org/freshwater-intertidal-mudflats/. Accessed May 29, 2023.