Estuarine Wetland Communities
The 2015 North Carolina Wildlife Action Plan defines 41 priority habitats for the state. More information about this habitat can be found in Section 4.3.2.
Contents
Habitat Priorities
Surveys
- Gather baseline information on sex ratios for species with temperature-dependent sex determination (all sea turtles, terrapins, alligators) to characterize impacts from climate change. (Surveys Priority)
Monitoring
- Continue monitoring beach-nesting birds due to their high vulnerability.
- Begin monitoring potential changes to offspring sex ratios for species with temperature-dependent sex determination (all sea turtles, Diamondback Terrapins, American Alligators).
- Collect spatial information on the distribution of estuarine habitats, document their characteristics, such as salinity, water levels, plant community struction and density, and monitor marsh die-back events.
Research
- Determine the migration pathways and wintering grounds for marsh birds.
- Investigate the mortality factors of sea turtles within the estuaries.
- Determine the habitat use, population levels, and distribution of priority marsh birds such as the Seaside Sparrow, Willet, Least Bittern, American Bittern, King Rail, and Black Rail.
- Investigate Nutria population densities, population growth rates, dispersal range, and extent of property damage from burrowing and herbivory.
- Conduct research to better characterize the use of estuarine habitats by American Alligators.
Management Practices
- Allow barrier islands to migrate, as it increases their chance of survival and reduces the chance of sudden and drastic changes in tidal regime in the estuaries.
- Where practical, restore marsh habitat by filling drainage ditches and installing ditch plugs and water control structures. Ditches may accelerate erosion and the effects of rising sea level such as saltwater intrusion.
- Protect suitable nesting habitat for sea turtles and beach-nesting birds to maintain robust populations as disturbance and sea level rise issues mount.
- Continue working with the US Army Corps of Engineers and others to direct dredged material or conduct other management actions to refurbish waterbird nesting islands.
- Continue coordination with the NC Division of Marine Fisheries to minimize bycatch of protected/priority species in fishing gear.
- Control or minimize the amount of large gull depredation on other beach-nesting birds. These large gulls did not nest in the state until recent decades but are now greatly increasing in number and are causing more pressure on beach-nesting bird populations.
Conservation Programs and Partnerships
Description
Estuarine wetland communities are affected by tidal waters in and along the sounds and drowned river mouths (see Section 4.2.14). The community includes brackish marsh, salt marsh, salt flats, and salt shrub components. In addition to the components described here, sand flats, mud flats, and algal mats are part of the estuarine community.
- Salt marshes occur where tides regularly flood the area with undiluted sea water. This environment of repeated flooding and exposure and higher salinity levels limit the diversity of plant species that occur in salt marshes to only a few species. Much of the productivity in salt marshes is likely below ground in organic materials. Saltmarsh and Saltmeadow cordgrasses dominate these communities, and only a few other vascular plants occur. Algae may also be an important part of plant productivity. The abundance of invertebrates such as mollusks and crustaceans indicates the transitional nature of these communities between terrestrial and marine systems.
- Brackish marshes occur in areas where the tidal waters are partly diluted by fresh water. They are low in plant diversity, with Black Needlerush usually dominating vast areas.
- Salt flats occur in fairly small areas of slight depression at the upper edge of salt or brackish marshes. Salty water floods these areas only occasionally. Once flooded, the water is trapped in the depression and evaporates, leaving salt concentrated in the soil. Vegetation is usually a sparse collection of extremely salt-tolerant plants such as Saltgrass and Glasswort. The center of the salt flat may be completely barren.
- Salt shrub communities occur on the upper edge of salt and brackish marshes, where saltwater rarely reaches or where salt is diluted by fresh water seepage. They are dominated by salt-tolerant shrubs with marsh herbs often occurring in openings.
Estuarine islands are not considered a wetland community but they are particularly important for nesting terns, skimmers, pelicans, wading birds, and American Oystercatchers. Most have been created by deposition of dredged material but there are a few that are natural islands. Dredged material islands are usually devoid of mammalian predators and have the added advantage of being high enough in elevation that ground nesting birds do not lose their nests during normal high tides. Estuarine communities were described as a priority habitat in the 2005 WAP (see Chapter 5) (NCWRC 2005).
Location of Habitat
Lower river portions of aquatic communities in the Roanoke, Tar–Pamlico, Neuse, Cape Fear, White Oak, Chowan, and Pasquotank river basins are associated with estuarine wetland communities. The shorelines of the Albemarle–Pamlico estuary system and the sound-side of the Outer Banks barrier islands are also fringed by estuarine wetlands.
Problems Affecting Habitats
Dredging
Dredging and dredge material placement can also affect these sites through draining of marshes or filling of wetlands. Dredged material placement has been used very effectively in some areas to create marsh or upland bird nesting areas within the estuaries. Competition with coastal towns that use dredged sand for nourishment projects along developed beachfronts and constraints to navigation channel dredging projects limits access to dredged material for bird nesting islands.
Land Use. Development has impacted much of this habitat type and armoring shorelines to prevent erosion is a growing problem. Predation by nonnative predators and disturbance by people and their pets of nesting birds and the lack of fire to maintain the vegetation structure in marsh sites is also of concern. Beach stabilization projects (e.g., inlet channel relocation and efforts to restrict channel movement) reduce availability of microhabitats such as mud and algal flats around inlets. Ditching can drain estuarine wetlands, disrupt normal hydrologic cycles, contribute to water quality problems by conducting point source discharges into nearby surface waters, and be a conduit for saltwater intrusion.
Water Quality
Water quality impacts from pesticide use (related to mosquito control), secondary impacts from development, and water flow impacts caused by ditching and canals have greatly affected this habitat. Failing septic systems, sewage treatment and marina cleanout effluents, stormwater runoff, industrial organic waste discharge, and agricultural fertilizers or animal wastes contribute excessive nutrients that can result in eutrophication and algal blooms. Mats of algae block sunlight from penetrating the water and will impact sea grasses. Low dissolved oxygen (DO) levels can result from algal die-off and decay and excessive algae growth can result in brown or red tides and harmful blooms, such as Pfiesteria piscicida, that have been associated with fish kills (EPA 2012b).
Climate Change
Climate change impacts, primarily sea level rise, will lead to shifts in plant composition and more open water habitats. An increase in the number of storm events and storm severity will result in more flooding and erosion of vegetation. The presence of drainage ditches will facilitate saltwater intrusion into more inland natural communities and rapid decomposition of peat soils by sulfate-reducing bacteria (Hackney and Yelverton 1990). Other problems will include subsidence and increased inundation of freshwater communities and release of previously sequestered carbon as carbon dioxide and methane (Hackney and Yelverton 1990).</p
Climate Change Compared to Other Threats
Climate change, particularly rising sea level and the potential erosion of barrier islands, is the greatest threat to estuarine wetland communities.
Impacts to Wildlife
Many bird species associated with these community types have experienced significant declines according to inventory and survey data. Several priority bird species, such as the Seaside Sparrow, Northern Harrier, American Bittern, and Black Rail, are ground nesters in estuarine marsh habitats. If marsh habitat does not migrate inland at comparable rates to habitat losses, these birds may be displaced permanently due to fragmentation and competition pressures. Waterbird species that are colonial nesters are vulnerable to loss of habitat because they have relatively few nesting locations. Beach-nesting birds, sea turtles, and terrapins are more likely to have their nests washed over as sea level rises.
Black Ducks also nest in brackish marshes. This species will lose nesting habitat as inundation drowns currently occupied marshes. Climate change will have a significant effect on brackish waterfowl impoundments, which provide high-quality habitats to breeding and wintering waterfowl and other shore and wading birds. Many of these areas will be lost to sea level rise.
Losses, drastic alteration, or disturbance of estuarine communities (especially marsh habitats) could have serious consequences for nutrient cycling and for reproduction of marine and estuarine organisms (Schafale and Weakley 1990). Some reptile species, including sea turtles, terrapins, and American Alligators, exhibit temperature-dependent sex determination. With predicted increases in overall temperatures associated with climate change, it is possible that offspring sex ratios of these species may be affected (Hawkes et al. 2009).
Several rare, disjunct, or endemic species—Carolina Watersnake, Aaron’s Skipper, and several moths—are associated with brackish marsh habitats in the sounds of the northern Coastal Plain. The drastic changes in salinity and wave action that are likely to occur if the Outer Banks are breached may drastically affect these species, possibly leading to their extirpation or extinction. If they survive the initial effects of the barrier island breach, however, they may be able to spread to new areas of brackish marsh that will form farther inland on the mainland side of the sounds.
Nutria are a nonnative and invasive mammal in freshwater and coastal marshes and wetlands, inland freshwater streams and rivers, and surface water impoundments. As warming trends increase, the range of Nutria is likely to expand and populations currently limited by intolerance to cold winters will quickly expand. There is some anecdotal evidence Nutria will take over and expand smaller next burrows of native wildlife such as Muskrats, thereby displacing native species. 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 (Carr 2010).