Aquatic Ecosystems

Tue, 11/08/2011 - 09:49 -- cadoughe

The health of aquatic ecosystems in the region can be adversely impacted by habitat destruction due to development, point and nonpoint source pollution, hydrologic alteration, and poorly managed agriculture and forest lands. Though water quality has improved in the past few decades, habitat degradation continues to threaten the overall health of these unique aquatic ecosystems. Other threats include impoundments on major rivers and tributaries that block fish migration patterns and cause habitat fragmentation.

Fortunately, increasing attention is being focused on analyzing aquatic systems, identifying the causes of endangerment, and applying conservation strategies. From national groups such as The World Wildlife Fund and the Nature Conservancy to more locally-based organizations like North Carolina Wildlife Resources Commission, there is research being conducted with the goal of preserving these valuable aquatic ecosystems. The following evaluations of the river basins in Western North Carolina are a brief summary of the threats identified in the North Carolina Wildlife Resources Commission Action Plan for Aquatic Habitat Conservation.

Health of River Basins

River basin health

Hiwassee River Basin

The Hiwassee basin is relatively stable with good water quality. It is impacted from non-point sources, primarily erosion, which increase as streams flow into the more developed valleys and merge into larger water areas. Erosion and sedimentation are primarily from ground disturbance from development activities (residential, commercial, transportation and utility) and agriculture (erosion from poorly managed pastures and row crops). Timber harvest with insufficient erosion controls may be another contributor of sediment to the basin, along with other non-point source pollutants such as runoff from built-up areas and roadways. Point-source discharges are not a current major pollutant of the Hiwassee basin.

Hydropower development has altered and degraded many habitats for most indigenous aquatic species. Un-impounded areas are affected by decreasing water temperature, altered hydrologic processes, and low levels of oxygen due to releases from the Chatuge and Nottely dams.

Invasive species are also potential threats to the native aquatic species living in the basin. The Blueback herring appears to have an impact on game species in the area, as well as the Asian clam and striped bass.

Little Tennessee River Basin

Major problems affecting species and habitats within the Little Tennessee basin include impoundment, and excessive erosion and stream sedimentation from development and agriculture. Of the entire 144 mile Little Tennessee River, there are only 47 miles in Georgia and North Carolina which remain un-impounded. Portions of the basin are currently at good quality levels, but it does have some impaired waterways including the Cullasaja River, Mill Creek, upper Little Tennessee River, Beech Flats Prong, and West Buffalo Creek arm of Santeetlah Reservoir.

Invasive, non-native species like the yellowfin shiner, which is expanding downstream from Franklin, are a potential problem to the basin. The Asian clam is established in both the Little Tennessee and Tuckasegee rivers, Chinese snails have been found in Cowee Creek, and the rusty crayfish is established in at least one area downstream from Fontana Reservoir. The native Spotfin chub was recently found to be infested with a tapeworm from Asia. Exotic pathogens and parasites pose serious threats to the rare species inhabiting the Little Tennessee basin.

Savannah River Basin

National forest and state park lands occupy the majority of the Savannah River basin, but development is increasing on private lands. Land clearing, removal of riparian vegetation, and rural roads are all potential non-point source problems. Numerous small impoundments fragment headwater regions. The basin’s major tributaries in North Carolina are also upstream from larger impoundments in Georgia and South Carolina. More monitoring is needed to address to what extent invasive species have become established in the Savannah River basin.

French Broad River Basin

The most widespread problem facing the French Broad River basin is habitat degradation from non-point source pollution. Large development, urbanization, and agriculture are also evident non-point sources of pollution and sedimentation. Highway development and construction pose significant threats to many areas of the French Broad basin, along with poorly managed steep slope development contributing runoff and sedimentation. Nutrient enrichment is a more serious issue in this basin than in any other basin in the region. Increasing in severity are threats from hydrologic modifications from activities such as impervious surfaces, flood plain filling, and stream channel alterations.

Not as widespread as non-point sources of pollution, point sources are still a significant problem causing habitat degradation in the basin. Impoundments pose a smaller threat to this basin than to other basins in western North Carolina, but are still cause for concern in some portions of the basin. Specifically within the French Broad River sub-basin, point source pollution, including both current and lingering effects from past pollution, contributes significantly towards habitat degradation and the extirpation of priority species.

The Pigeon River sub-basin has a long history of point source pollution. Toxic wastes were discharged directly to the Pigeon River for much of the 20th century, eliminating many priority aquatic species. Treatment began in the early 1990’s to improve water quality, and the recovery of many native species has been favorable, though the river continues to be heavily monitored.

More research is needed to fully assess affects of invasive species in the French Broad River basin. The native long-ear sunfish has been displaced entirely by the non-native redbreast sunfish and a few other invasive species have been established in segments of the basin, but exact influences on game versus non-game communities are not known.

Broad River Basin

The predominant impact on water quality in the Broad River basin is habitat degradation from sedimentation originating from construction, row crop agriculture, timber harvest, mining, stream bank erosion, and runoff from unpaved rural roads. Stream bank vegetation is either significantly or entirely lacking throughout the basin, leaving the waters more susceptible to runoff. Water quality is declining due to channel alterations in both rural and urban areas of the basin, combined with the escalating amount of impervious surfaces which lead to drainage problems.

Waste water treatment plants and industrial discharges are the primary point source polluters. Aquatic communities are impacted from impoundments at Lake Lure, Kings Mountain and Lake Adger. With a steadily increasing human population, demand is growing for water supply from surface waters. Water withdrawals, impoundments, and interbasin water transfers will have a serious effect on species in these aquatic areas.

Catawba River Basin

The most severe threat facing the Catawba River basin is impoundment. Almost the entire basin is either impounded or regulated by hydropower projects. The release of colder water causes wildlife degradation as many native species are unable to adapt to the abrupt changes in water temperature. Migration routes are limited if not completely impassable due to dams. Other causes of degradation in the basin include sedimentation from ground disturbance from development and agriculture, loss of streamside vegetation, water withdrawals, point source pollutants (waste water treatment plants and permitted industrial dischargers), and nutrient loading.

The numerous non-native species inhabiting the basin includes Asian clams, grass carp, blue, channel, and flathead catfishes, smallmouth bass, muskellunge, white bass, yellow bass, rainbow and brown trout. Blueback herring, alewife and white perch are also known from several impoundments. There is non-native flora species present in the Catawba River basin as well, particularly in the reservoirs, but the specific effects on the native communities require further research.

Watauga River Basin

At present, water quality conditions of the Watauga River basin are very favorable, but there are lingering affects from past pollution occurrences. Sedimentation and erosion from non-point sources is a primary threat affecting the basin. The drastic lack of streamside vegetation, and overly narrow riparian corridors have caused excessive erosion and habitat loss due to sediment deposition and the over-widening of water channels. Residential and agricultural development is on the rise, which also raises the threat of habitat loss through increasing erosion. Christmas tree farming in the basin may also add pesticide and herbicide pollution to streams.

New River Basin

Although it exhibits overall good water quality, the New River basin is affected by localized problems and habitat degradation in many of the streams inhabited by priority aquatic species. Development and land clearing, poorly managed livestock grazing, unpaved rural roads, and loss of streamside vegetation all contribute to ecosystem degradation. New home construction, primarily on steep slopes, is increasing steadily. Sedimentation impacts are very serious, particularly in larger tributaries and in the main stem of the New River. There are also increases in water withdrawals as a result of larger populations moving into the area, a problem primarily in the upper South Fork New sub-basin.

Degradation in water quality is a result of acid mine drainage, urban runoff, and discharges from waste water treatment plants. Like the Watauga River basin, herbicides and pesticides used in Christmas tree production also impact the New River basin, but to what degree is still uncertain. Threats also emerge from the numerous non-native aquatic species which are established throughout the basin.

Yadkin River Basin

There is limited information and inadequate surveys on aquatic species distribution in the upper region of the Yadkin. Invasive species have undoubtedly become established in the basin, and are likely having a negative impact on native populations, though the exact effects are unknown. Dams and impoundments to the east of the region pose a serious threat to the Yadkin River basin.

Atmospheric Deposition

Acid-neutralizing capacity

The atmospheric deposition of acidic compounds (sulfates and nitrates) and ammonia, originating predominantly from the combustion of fossil fuels and livestock production, can impact water quality. The acidifying compounds are deposited on soils and can be transported into the soil water in the watershed before traveling down slope into the stream or ground water. All watersheds in the region have been impacted by acidic deposition; however, some streams have a significantly higher ability to buffer or neutralize acidic compounds than others. Stream buffering capacity is determined by surrounding soil types and underlying bedrock. For example, stream beds which develop from carbonate rocks (those high in calcium, magnesium, potassium, and sodium) have a high capacity to mitigate acid inputs, and are not currently vulnerable to the effects of increased acidity.

Some aquatic organisms, such as aquatic insects, are highly sensitive to changes in stream water chemistry; while native brook trout, in particular, are somewhat tolerant of acidic conditions. The relationship between brook trout health and survival has been studied in streams with differing buffering capacities. Streams with adequate buffering capacity will have healthy trout populations if other habitat factors are favorable for their survival. However, negative impacts on native trout populations increase as stream water becomes more acidic and toxic metals such as aluminum appear.

Between 2000 and 2005, the USDA Forest Service found that, of streams sampled, 47 percent had adequate buffering capacity to mitigate future acidic deposition. However, about 53 percent of sampled streams were classified as potentially, episodically, or chronically sensitive to acidification. These vulnerable headwater streams were found predominantly at elevations greater than 3500 feet on soils with low buffering capacity.

By the year 2100, while sulfate deposition from the atmosphere is predicted to decrease significantly, stream sulfate concentrations are predicted to decrease only in streams currently classified episodically or chronically acidic. Sulfate concentration in potentially sensitive streams is predicted to remain constant or increase slightly during the same time period. The lack of responsiveness of stream sulfate concentrations is attributed to soil retention of a portion of sulfate depositions. It may take centuries for stream sulfate concentrations to decrease significantly even though the total sulfate deposition has decreased and is predicted to decrease in the future. A significant decrease in stream water sulfate concentration will not occur until historical sulfates bound to the soils are removed through natural processes.

Species at Risk

WNC federally-listed species at risk

The dense network of rivers and mountain streams in Western North Carolina support highly diverse aquatic ecosystems including many species of fish, mussels, snails, crayfish, amphibians, and reptiles.

The increasing threat to aquatic communities in the region is primarily due to habitat degradation and destruction, point and nonpoint source pollution, dams and impoundments, and the introduction of non-native species.

Fish commonly found in the region include native brook and non-native brown and rainbow trout, bass, crappie, many species of perch, catfish, minnows, darters, and suckers.

Native brook trout, which once thrived in cold mountain streams across the region, have been severely impacted and are now found in less than 80% of their historic range. The majority of populations are currently found in the Nantahala and Pisgah National Forests and the Great Smoky Mountains National Park. Sensitive to changes in stream chemistry, stream temperature, competition from other trout species, and land use change, native brook trout continue to need protection and restoration.

Freshwater mussels, found in the shallows of streams and rivers, require cool, clean, well-oxygenated water with riffles, runs, and shallow flowing pools with stable, silt-free, rocky stream beds. Stream bed stability is critical to mussel survival and they are seldom found in areas with accumulations of silt or shifting sand. Freshwater mussels, especially in their early life stages, are extremely sensitive to chemicals found in wastewater such as chlorine, ammonia, heavy metals, or high concentrations of nutrients. The destruction of river habitats by dams, channelization, erosion, and pollution has left several species of mussels on the brink of extinction.

Crayfish are freshwater crustaceans found in streams, rivers, swamps, ponds, and other aquatic habitats with flowing water and cover. The small range of many crayfish species is a primary factor in their vulnerability to habitat loss and competition. Threats to crayfish include pollution, impoundment, and competition with non-native species.

The southern Appalachian region is the world’s center for salamander diversity. According to the Southern Appalachian Biodiversity Institute, nearly 10% of global salamander diversity and 10% of freshwater mussel diversity occur here. Salamanders are inhabitants of springs, seepages, and streams. They live in bottomland as well as high elevation forests throughout the region. Species diversity is high because many species are at the southern limit of their distribution and gradients in elevation, aspect, slope, and rainfall contribute to a range of available niches and habitats.

Snails play a dominant role in the ecology of the region’s freshwaters by providing food for many other animals and by grazing on vast amounts of algae and debris. They are critical to normal ecological processes in rivers and as indicators of water quality. Freshwater snails are in decline, especially those that inhabit streams and rivers. Dam construction and other channel modifications, siltation, and industrial and agricultural pollution have degraded the river habitats on which most species depend.

The continued loss and decline of freshwater snails, mussels, fish, crayfish, amphibians, and reptiles demonstrates that despite significant water-quality improvements made in the last 28 years since the passage of the Clean Water Act, species loss is still a critical concern in the region.

The U.S. Fish and Wildlife Service currently lists 11 fish, 7 mussels, 2 crayfish, 4 salamanders and 5 snails as federally threatened, endangered, or species of concern in river basins across the region. Many of these are found in the Hiwassee, Little Tennessee and French Broad basins. Additionally, the state of North Carolina has identified at least 50 additional aquatic species of priority concern in the nine river basins in Western North Carolina.