John Heinz National Wildlife Refuge protects the largest remnant of freshwater tidal marsh, roughly 285 acres (one-third square mile) that remains in this part of the State. A marsh is a type of wetland that is dominated by herbaceous rather than woody plant species. Freshwater tidal marshes are some of the most biologically productive ecosystems in the world: containing high plant diversity and supporting more bird use than any other wetland type. Marshes also improve water quality by acting as a sink to filter pollutants and sediment from the water that flows through them. Marshes (and other wetlands) are able to absorb water during periods of heavy rainfall and slowly release it into waterways and therefore reduce the magnitude of flooding.
Freshwater tidal wetlands comprise approximately one-third of the refuge. Protection of this habitat is one of the primary purposes outlined in the refuge’s mandated purposes. The marsh contains some ecological communities considered State critically imperiled and globally rare and occurrences of State/federally rare, threatened, and endangered plant and animal species. These wetlands are subject to a range of tidal fluctuation on a daily basis of approximately 6 feet between mean high tide and mean low tide. Vegetation is diverse, with species and plant communities directly influenced by the relative elevation of mean high tide.
Most freshwater tidal marsh is dominated by pickerelweed, arrowhead, spadderdock, or wild rice. However, portions of this marsh support several State rare species such as waterhemp ragweed (Amaranthus cannabinus), field dodder (Cuscuta pentagona), Walter’s barnyard-grass (Echinochloa walteri), an un-named eupatorium (Eupatorium rotundifolium), forked rush (Juncus dichotomus), and shrubby camphor-weed (Pluchea odorata) (VanDervort-Sneed personal communication 2010).
Many of the areas in and around the refuge were historically freshwater tidal marsh. Loss and alteration of wetlands dates back centuries, as early as the ﬁrst Dutch settlements of the 1640s, when many marsh areas around the Tinicum region were diked for agriculture. More recent losses of tidal marsh occurred between the 1950s and early 1970s, when several areas of the refuge were ﬁlled or dredged. As a result of these large-scale disturbances, altered hydrology, invasive species introductions, and high levels of deer browse continually impact many of the natural communities within the refuge.