Floodplains-Blackwater Systems
The 2015 North Carolina Wildlife Action Plan defines 41 priority habitats for the state. More information about this habitat can be found in Section 4.3.3.
Contents
Habitat Priorities
Surveys
- Document Bald Eagle nesting sites. (Surveys Priority)
- Survey for poorly known or secretive semi-aquatic snakes—Rainbow Snake, Glossy Crayfish Snake, and Black Swamp Snake. (Surveys Priority)
- Determine the breeding and roosting status and distribution of Chimney Swifts in natural conditions along major floodplains with appropriate habitat conditions (e.g. older, hollow trees). (Surveys Priority)
- Design specific surveys to determine status and distribution of birds not adequately picked up by the Breeding Bird Survey in floodplain forests (e.g., the Cerulean Warbler, Swainson's Warbler, Kentucky Warbler, Worm-eating Warbler, Hooded Warbler, Prothonotary Warbler, etc.). (Surveys Priority)
- Survey for bat species that roost or forage in blackwater systems. (Surveys Priority)
Monitoring
- Continue nest monitoring for colonial waterbirds, especially Wood Storks.
- Continue long-term monitoring of active Bald Eagle territories, successful breeding pairs, and fledged eagles.
- Establish Monitoring Avian Productivity and Survivorship (MAPS) and migration banding stations, as well as specialized long-term monitoring for hard-to-sample species such as the Cerulean and Swainson's warbler (Graves 2001).
- Investigate the past, current, and potential future impact of nutria on both floral and faunal communities and individual species.
- Determine the conservation and restoration efforts needed for priority species in this habitat.
- Make an attempt to protect waterbird nesting colonies.
Research
- Research the genetic makeup of the coastal population of the Black-throated Green Warbler.
- Research the genetic relationships among floodplain salamanders.
Management Practices
- Explore techniques for restoration of tidal swamp forest and wetlands.
- Wherever possible, maintain or restore floodplain forest connectivity, as floodplain forests are important distribution and dispersal corridors for many species (Bailey et al. 2004). This would benefit floodplain forest species such as the Northern Parula, Yellow-Throated Warbler, Prothonotary Warbler, Wood Thrush, Swainson's Warbler, and Acadian Flycatcher, as well as amphibians, Timber Rattlesnakes, and forest bats.
- Ensure floodplain buffers of 300 to 600 feet in as many areas as possible. Where possible, forest patches should be connected along river systems to provide connectivity.
Conservation Programs and Partnerships
Description
Floodplains are defined as “areas of low lying land that are subject to inundation by lateral overflow water from rivers or lakes with which they are associated” (Junk and Welcomme 1990; Tockner and Stanford 2002). Other terms frequently used to refer to floodplains include alluvial forests, bottomlands, fluvial systems, riverine forests, or stream or riparian zones. Floodplains can be comprised of more than one community type since the timing, depth, and duration of flooding are considered the primary influence on plant species composition (Wharton et al. 1982; Kellison et al. 1998; Mitsch and Gosselink 2000; Burke et al.2003). The floodplain community will also be influenced by variations in soils and microenvironments that occur in the landscape adjacent to the aquatic community. In its natural state, floodplains have high biodiversity and productivity as well as providing recreational and aesthetic values (Tockner and Stanford 2002).
Blackwater floodplains include the vegetated communities on the floodplains of blackwater rivers. Blackwater rivers are low gradient rivers in small watersheds where hydroperiods are characterized by short duration floods that may be deep and widespread, followed by extensive periods of lower discharge (Burke et al. 2003). The flow often is not sustained, and extended droughts during the growing season can occur in these floodplains (Wharton et al. 1982; Burke et al. 2003).
Contrary to brownwater rivers, they carry little mineral sediments (e.g., clay and silt). Instead, the water chemistry in blackwater rivers is dominated by dissolved organic matter leached from decomposing vegetation and is generally low in pH and nutrients. The water is tea-colored but not cloudy. The soils of blackwater floodplains are usually sandy or mucky and are acidic and relatively infertile. Many floodplains, particularly the larger ones, have at least some development of depositional features such as natural levees, point bars, and ridge-and-swale systems, but these are not as large or prominent as on brownwater rivers. Many smaller blackwater floodplains are filled with muck and are flat and featureless.
Communities that occur in blackwater floodplains include: Coastal Plain levee forest and bottomland hardwoods on the larger floodplains, cypress-gum swamps in the wettest and forested parts of the floodplain, Coastal Plain small stream swamps, Coastal Plain semi-permanent impoundments (e.g., Beaver ponds, millponds), oxbow lakes along the large rivers in abandoned channel segments, and sand and mud bars along the rivers (Schafale and Weakley 1990).
Location of Habitat
Blackwater rivers originate in the Coastal Plain ecoregion and many are located in the lower portion of the river basins that drain to the Atlantic coast. Examples of blackwater streams and rivers include the South River, Black River, Waccamaw River, and the Northeast Cape Fear River. The Lumber River mainstem is the only North Carolina blackwater river designated as a National Wild and Scenic River.
Problems Affecting Habitats
The floodplain forest systems of the Coastal Plain in the southeast are now only small fragments and sections of the original millions of acres present before European settlement that have been lost or altered by development, drainage, agriculture, and logging (Weller and Stegman 1977).
Climate Variability
Milder winters will result in potentially longer growing seasons and earlier bloom times for plants and earlier breeding periods for reptiles and amphibians. Most species in this habitat type have a southeastern distribution and are fairly well adapted to higher temperatures. Increased temperatures will likely result in decreased winter kills of nonnative species and will likely allow these species native to areas further south to survive and reproduce. Insect infestations may increase and negatively affect forest health. Drought conditions will allow invasion of upland species (e.g., Red Maples and beech). Some more southern species may migrate into these communities. Conversion of lower river areas to tidal marsh will allow the Common Reed to invade. Increased temperatures and decreased winter kills will allow southern species to move farther north (e.g., the Asian Dayflower, Japanese Climbing Fern, Chinese Tallow Tree).
Storms
Increased hurricane intensity will increase blow down, especially near the coast. Bottomland hardwoods are more likely to be affected by windthrow than other floodplain communities. Increased canopy gaps may result from increased storm wind damage and from flood scouring. Flooding could benefit canebrakes and their associated species, but both the magnitude and direction of the effects are uncertain. Species composition could change following storm damage, resulting in loss of mast-producing species. Increased severity of flooding may destabilize channels, alter sediment load and deposition, and increase erosion. Increased frequency may have beneficial effects but increased duration may kill species not adapted to long periods of inundation. More large floods might mean increased river area with increased instability of bars. This would come at the expense of forests along the river banks, which are often the least altered forests in the floodplains. If flood frequency increases, it might also cause the boundaries between bottomland hardwoods and cypress-gum swamp to shift. Effects on species composition are unknown but changes to the overall community structure are likely, especially in lower reaches that may eventually convert to marsh.
Sea Level Rise
Saltwater intrusion associated with sea level rise is expected to have significant adverse effects on lower reaches of blackwater floodplains where it is likely to affect long-term survivability of canopy species. Saltwater intrusion will affect long-term survivability of canopy species in the lower floodplain reaches. Wetlands close to the Cape Fear River near [w:Wilmington] and the lower portion of the Scuppernong River near Columbia have already been impacted. No expansion of this community type is possible upstream and expansion into the Piedmont is not possible for this ecosystem. Consequently, the net effect from climate change will be an overall loss of acreage. Because there is not substantial potential for the floodplain systems to expand inland, there will be a net loss in area.
Climate Change Compared to Other Threats
Comparing climate change to other ecosystem threats can help define shortand long-term conservation actions and recommendations. While climate change is not the most severe threat, a combination of synergistic effects with other existing conditions could stress these systems to the point where several species are unable to persist.
Changes in flood regimes and rising sea level are the most important climate effects. Most Coastal Plain wetland communities, including blackwater systems, may be moderately vulnerable to climate change, depending on importance of precipitation and riverine flooding for hydrologic inputs. Direct loss of wetlands due to sea level rise is expected to be the greatest threat in coastal landscapes (DeWan et al. 2010). However, these systems will remain common.
Impacts to Wildlife
Loss of old growth characteristics (canopy gaps, vine tangles, hollow trees, dead and downed woody material) and fragmentation of stands is a major concern. A lack of standing dead or older trees has impacted the availability of quality bat and Chimney Swift roosting and breeding sites and nesting productivity for species such as Wood Duck and Hooded Merganser. Removing woody debris from streams after storms has influenced in-stream habitat structure and food webs. Lack of downed woody debris has impacted a variety of amphibians and reptiles.
Fragmentation of floodplain forest stands has contributed to the loss of intact large riparian corridors and the width of many riparian corridors has been greatly reduced. Breeding area-sensitive bottomland-hardwood birds have likely been impacted by the loss of intact woodland systems. Large patches of floodplain habitat are lacking in much of the Coastal Plain. High-grading logging practices have changed plant species diversity and stand vegetative structure. Logging has reduced colonial waterbird and Bald Eagle nesting areas.
Alteration of hydrology due to dam creation and the draining of wetlands are one of the primary problems affecting species in this habitat type. The impacts of development adjacent to rivers and streams includes potential problems associated with direct input of contaminants and sediment, alteration of hydrologic patterns and processes, temperature regimes, and loss of critical habitat adjacent to aquatic habitat that may be of equal importance to species that only spend a portion of their lives in the water, like some amphibians. Drainage of wetlands has exacerbated the problems in and adjacent to floodplain forest habitats. This habitat loss impacts all floodplain species, including furbearers, breeding amphibians, overwintering birds, and migrant species that use these areas as stopover sites. Water quality is also an issue in certain major river drainages that negatively affects many invertebrates, fish, amphibians, and reptiles.
This ecosystem contains some extremely rare disjunct and near endemic plant species. Their rarity makes them vulnerable to changes in habitat. Random events in specific locations can have major impacts on the expected viability of whole species. Two cane-feeding moths are endemic (or nearly so) to the North Carolina Coastal Plain. Habitat for these species is divided between blackwater and brownwater floodplains, as well as peatlands. All of these species, plus the larger guild of cane-feeding insects, is likely to benefit from increased canopy gaps and other disturbances associated with climate change.
Diversity of “native” species may potentially increase due to movement of more southerly species northward into this habitat type (e.g., Wood Stork, Swallow-tailed Kite, water elms, water locusts). The Wood Stork has expanded its breeding range in the state and is now nesting at several blackwater stream/river sites. More substantial changes may occur in floodplains north of North Carolina, beyond the current range of widespread southern floodplain species.