Little Hunting Creek experiences the same ebb and flow of lunar tides which influence the Potomac River up to Washington, DC. Given its position in the uppermost reaches of the estuarine zone, wetlands along the creek are inundated by freshwater (salinity less than 5 ppt) which backs up as it meets resistance from the incoming tide. As a result, the wetlands which have developed along Little Hunting Creek are largely distinct from the brackish and saltwater marshes found closer to the Chesapeake Bay.
Over the next two years, vegetation ecologists will survey tidal wetlands occurring on Fairfax County Park Authority (FCPA) property along Little Hunting Creek. Ecologists will map the extent of the wetlands and conduct inventories of the plant species occurring within each wetland type.
Types of Freshwater Tidal Communities at Little Hunting Creek
At least six types of freshwater tidal communities are expected to occur along Little Hunting Creek based on previous work conducted nearby. For each of the community types discussed below, a Community Element Global (CEGL) code is provided. These codes are unique identifiers for community types which can be searched using the United States National Vegetation Classification or NatureServe Explorer. The communities are listed based on their typical topographic position from lowest elevation (along the creek) to highest (bordering uplands).
Tidal Freshwater Marshes
These communities are dominated by herbaceous species and are subject to diurnal flooding associated with the tides. At least four types of tidal freshwater marsh are expected to occur along Little Hunting Creek:
1. Common Spatterdock Mudflat Type (CEGL004472) – G4G5/S3
This community type typically occurs on mudflats located below mean-low water where the substrate is infrequently exposed. The vegetation is generally dominated by Spatterdock (Nuphar advena) which often forms large, clonal stands. Submerged aquatic species like Coontail (Ceratophyllum demersum), Pondweeds (Potamogeton spp.), and the invasive Hydrilla (Hydrilla verticillata) may also be present.
2. Arrow-Arum – Pickerelweed Type (CEGL004706) – G3G4/S3S4
This community type is typically dominated by Arrow-Arum (Peltandra virginica) and Pickerelweed (Pontedaria cordata), but occurrences along smaller waterways can often be dominated by Nuphar advena. This natural community differs from CEGL004472 which occurs on lower landscape positions, experiences longer periods of inundation, and has lower plant diversity.
Tidal freshwater swamp, Arrow-Arum – Pickerelweed Type
3. Sweetflag Type (CEGL006833) – GNR/SU
This marsh is dominated by the introduced Sweetflag (Acorus calamus). While occurring at higher elevations, it tends to be inundated longer than the mixed high marsh. Other species such as Rivershore Bulrush (Bolboschoenus fluviatilis), Broadleaf Arrowhead (Sagittaria latifolia), and Dotted Smartweed (Polygonum punctatum) can remain frequent and often overtop the Sweetflag later in the season.
4. Mixed High Marsh Type (CEGL006325) – G3/S3
As the name implies, the mixed high marsh occupies higher elevations and has a variable composition – often exhibiting patch dominance. Species such as Orange Jewelweed (Impatiens capensis), Rivershore Bulrush (Bolboschoenus fluviatilis), Narrowleaf angustifolia (Typha angustifolia), Wild Rice (Zizania aquatica), and Swamp Rose-mallow (Hibiscus moscheutos) are among the most common species in this community type.
Swamp Rose-mallow (Hibiscus moscheutos) flowers
Freshwater Tidal Shrub Swamp (CEGL006843) – GNR/SU
This shrubland community often occurs as a border or ecotone between herbaceous tidal marshes and forested tidal swamps or upland habitats. Composition can vary, but common species include Smooth Alder (Alnus serrulata), Black Willow (Salix nigra), Buttonbush (Cephalanthus occidentalis), Silky Dogwood (Cornus amomum), and Swamp Rose (Rosa palustris).
Freshwater Tidal Hardwood Swamps (CEGL006287) – G3/S3
These forested swamps are often sandwiched between herbaceous tidal marshes and upland habitats and are characterized by hummock and hollow topography. This community was formerly dominated by Green Ash (Fraxinus pennsylvanica) and Pumpkin Ash (Fraxinus profunda) prior to the introduction of the Emerald Ash borer, though both species remain common as shrub-sized individuals which still manage to set seed. The dominant tree species now tend to be Red Maple (Acer rubrum) and Blackgum (Nyssa sylvatica), usually occurring at low density. Common shrub species include Winterberry (Ilex verticillata), Southern Arrow-wood (Viburnum recognitum), Smooth Alder (Alnus serrulata), and Silky Dogwood (Cornus amomum). Given sparse canopy cover, the herbaceous layer can be particularly dense with grasses (Glyceria striata, Leersia oryzoides, Zizania aquatica), sedges (Carex crinita, C. tribuloides, C. laevivaginata) and Water-hemlock (Cicuta maculata).
Zizania aquatica in a freshwater tidal hardwood swamp
A freshwater tidal hardwood swamp
The Importance of Wetlands and the Challanges They Face
The wetland types described above are quite unique and have a limited distribution given their dependence on tidal freshwater. They also provide a range of ecological services that benefit both man and the environment; they act as natural filters, improving water quality by trapping sediment, absorbing nutrients, and breaking down pollutants. They also serve as vital habitat for wildlife, including migratory birds, fish, and amphibians among others. Tidal marshes also play a role in flood control by absorbing excess water during high tides, reducing the impacts of storms and flooding. Additionally, they contribute to carbon sequestration, storing large amounts of carbon in the soil and existing vegetation.
Unfortunately, a number of factors can negatively impact freshwater tidal systems. These include sea-level rise, invasive species, and nutrient-loading from polluted runoff. Additionally, tidal wetlands that have been hydrologically altered by factors like undersized road culverts have experienced reductions in both size and quality.
Conclusion
The tidal freshwater wetlands of Little Hunting Creek are a unique and vital component of the region’s ecology, hosting a variety of wetland types that contribute to the area’s biological diversity and health. These wetlands, from emergent herbaceous marshes to forested swamps, support a wide range of species and play critical roles in water quality improvement, flood mitigation, and carbon sequestration. As urban development and environmental pressures continue to affect the watershed, it is essential to recognize and protect the diverse wetland types found here. In doing so, we can ensure the preservation of these important ecosystems which provide numerous benefits to both wildlife and the people of Fairfax County.
This post was written by Nelson DeBarros, Vegetation Ecologist with the Natural Resources Branch of the Fairfax County Park Authority.
