Freshwater Tidal Wetlands
The 2015 North Carolina Wildlife Action Plan defines 41 priority habitats for the state. More information about this habitat can be found in Section 4.3.6.
Contents
Habitat Priorities
Surveys
Monitoring
- Begin long-term monitoring, following survey data, for all marshbirds, mammals, and reptiles in this habitat type.
Research
- Investigate how reduction in freshwater marsh and increases in higher salinity areas affect alligators.
- Conduct research on fire management in marsh habitats to determine optimal frequency, timing, and firing techniques (e.g., flanking fire, back fire) to benefit priority birds.
- Investigate population densities, population growth rates, dispersal range, and extent of property damage from Nutria burrowing and herbivory.
- Determine what circumstances cause organic soils to rapidly decay in coastal wetlands.
Management Practices
- Explore techniques for restoring tidal swamp forest and wetlands.
- Consider planting bald cypress to create the next shoreline as sea level rises and blocking ditches to slow saltwater flow into the interior of freshwater tidal marsh as a measure to reduce erosion and buy time for habitat migration inland.
- Use prescribed fire to burn portions of tidal freshwater marshes to eliminate or set-back competing woody species. Mechanical cutting of woody vegetation may be more feasible in wetter areas that cannot be reached by fire.
- The use of bulkheads should be discouraged when other possibilities are available.
Conservation Programs and Partnerships
Description
Freshwater tidal wetlands occur in sites where flooding occurs in response to lunar or wind tides, but where the water has less than the 0.5 parts per thousand (ppt) salt content used to define freshwater. Tidal freshwaters occur in rivers, where freshwater flow keeps out saltwater, and along the large sounds where distance from seawater inlets keeps the water fresh. Components of this habitat include: tidal cypress-gum swamps and tidal freshwater marshes:
- Tidal cypress-gum swamps occupy vast areas at the mouths of large rivers and also occur at the mouths of smaller creeks and occasionally along the sound shoreline. They are dominated by Swamp Black Gum, Water Tupelo, and Bald Cypress. Understory tree, shrub, and herb layers are generally sparse and low in diversity.
- Tidal freshwater marshes occur in the lowermost parts of some tidal rivers and creeks and, more commonly, in large flats along the shorelines of freshwater sounds. The vegetation is generally strongly zoned and often very diverse in at least some zones. Two distinct variants are recognized, one with very slightly salty (oligohaline) water, the other completely fresh. The 2005 WAP describes tidal swamp forest and wetland communities as a priority habitat (see Chapter 5) (NCWRC 2005).
Location of Habitat
These habitats occur along rivers or sounds in areas where flooding is influenced by lunar or wind tides. Fresh water input may heavily influence the salt content (NCWRC 2005). Tidal cypress–gum swamps are extensive along shorelines and along drowned river valleys (e.g. Cape Fear, Neuse, and Chowan rivers). The most extensive examples can be found around Albemarle Sound areas, Alligator River, and at the mouths of the Cape Fear, Neuse, Tar, and Roanoke rivers. Tidal freshwater marshes are common around the margins of Currituck Sound, and occur in smaller areas, such as in the Cape Fear River just west of Wilmington.
Problems Affecting Habitats
Erosion
Erosion control measures may help protect these communities, but measures that alter the shoreline, whether sea walls, “soft” structures, or planting off-site species, are potentially destructive to these communities. Shoreline armoring and hardening to protect infrastructure will prevent ecosystems such as tidal marshes from migrating inland (DeWan et al. 2010). As development continues inland, water demands in the Piedmont will affect freshwater flows from the major rivers that feed this system through water removals.
Flooding
Alteration of flood regimes in rivers may affect these systems. Some areas are fresh largely, or at least partly, because of the dilution of sea water by river input. Increased water withdrawal or interbasin transfer may increase this problem in the future. The effects are local, affecting primarily the mouth of the altered rivers, but could be important cumulatively. Existing drainage ditches and canals bringing saltwater into wetlands is a serious threat. Saltwater intrusion is already impacting former forests in Alligator River National Wildlife Refuge near the intersection of US 64 and US 264, and in the lowest portion of the Scuppernong River at Columbia. Tide gates or blocking ditches are needed to slow, if not eliminate, some saltwater intrusion. However, saltwater intrusion into Albemarle Sound and into the Scuppernong River cannot be controlled by tide gates or blocking ditches.
Logging
This ecosystem group is likely to experience drastic changes in extent and significant movement of communities that are logged. Logging is a threat to some tidal cypress– gum swamps, while others are in protected status or are too wet for logging equipment. Drying may create opportunities for logging these wet areas.
Small plants of low interior marshes appear to need fire to maintain their habitat. Lack of fire allows unnatural vegetation succession in some freshwater marshes. Common Reed, Chinese Tallow Tree, Alligator Weed, and Nutria are primary invasive species concerns.
The disruptions created by shifting communities and catastrophic events may increase the spread of Common Reed. Giant Salvinia could become a problem. Early control of species that have proven more invasive farther south will be less costly and less ecologically disruptive than allowing populations to become large.
Climate Change Compared to Other Threats
Changes caused by rising sea level are the greatest threat, but increased intensity of storms, both in rainfall and wind, are also important. Because these systems are so subject to sea level, tidal movement, water salinity, and storms, these effects of climate change are the greatest threats.
Impacts to Wildlife
No terrestrial animals are endemic to this ecosystem group within North Carolina. Manatees, Roseate Spoonbills, and possibly other species may be able to persist in North Carolina in the future climate with warmer weather. Coastal freshwater wetlands provide important habitats for bitterns, rails, and a variety of other wading and shore birds. Conversion of other habitats, especially tidal forests, to tidal freshwater marsh will occur over time, which means availability of this habitat for nesting, cover, and forage may briefly increase; however, in the long term, location and amount of such marshes is uncertain (DeWan et al. 2010).
Tidal freshwater wetlands provide nursery habitat for aquatic species that live in saltwater but rely on fresh and brackish waters for larval recruitment and development. Many of these species are economically or commercially important, such as crabs, shrimp, and flounder species (DeWan et al. 2010). Coastal freshwater wetlands are also important to furbearers, waterfowl, and other game species.
The Rare Skipper (Problema bulenta) occurs solely within tidal freshwater marshes throughout its range, from New Jersey to southern Georgia. Dukes’ Skipper (Euphyes dukesi) is also restricted to these habitats along the Atlantic coastal portion of its range, although it also occurs inland in Florida, and in the Midwest region. Although the reasons for these restrictions are not clear, the larvae of both species feed on plants that occur well inland from the coast, even in North Carolina. Both of these species are potentially susceptible to extirpation from the state if they or their specialized habitats cannot keep pace with the effects of sea level rise and saltwater intrusion.
Nutria are considered a serious pest species in the United States because they eat a variety of wetland and agricultural plants and their burrowing damages streambanks, impoundments, and drainage systems. Nutria may also be a vector for diseases (tuberculosis and septicemia) or parasites (Giardia, Fasciola, Liver Flukes, and nematodes), with fecal contamination in water the likely pathway. As warming trends increase, the range of Nutria is likely to expand and populations currently limited by intolerance to cold winters will quickly expand (Carr 2010).