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The Ecology of the Cape Fear River System By Dr.
Michael A. Mallin GEOGRAPHY OF THE CAPE FEAR SYSTEM |
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The Cape Fear Estuary drains the largest watershed in North Carolina, containing 27% of the State's population. The Cape Fear River itself (about 320 km or 200 miles in length) is formed in the Piedmont by the confluence of the Haw and Deep Rivers in Chatham County (Fig. 1). Two major tributaries join the Cape Fear just upstream of the City of Wilmington, the Black River and the Northeast Cape Fear River (Fig. 2). These two tributaries lie primarily in the Coastal Plain and are considered blackwater systems; the Black River drainage represents about 17% of the Cape Fear system drainage area and the Northeast Cape Fear about 18%. Because of the open connection with the Atlantic Ocean, tidal effects are felt 105 km (65 miles) upstream along the Cape Fear proper to Lock and Dam #1, and about 80 km (50 miles) upstream along the Northeast Cape Fear (Fig. 1). The watershed and estuarine system lie entirely within the borders of North Carolina. The Cape Fear differs from most other major estuaries in North Carolina in that it is open to the sea, has a significant tidal effect, and drains broad areas of coastal plain, making it largely a blackwater system. The Cape Fear is typical of the kind of systems found in the southeast U.S. stretching from lower North Carolina, through South Carolina and Georgia, and into North Florida. Most of the other large estuaries in North Carolina are bordered by barrier islands, have more restricted flow, and are less affected by tides. LAND USE IN THE LOWER CAPE FEAR BASIN Table 1. Natural land cover data for the Cape Fear River and Estuary. ____________________________________________________________ Total drainage area 23,310 km2 (9,000 mi2) Wetland area Tidal swamp 12,140 ha (30,000 acres) Salt marsh 4,870 ha (12,030 acres) Tidal freshwater marsh 1,200 ha ( 2,970 acres) Volume of tidal waters 3.44 x 108 m3 (9.1 x 1010 g) Surface area of tidal waters 98.5 km2 (38 mi2) ____________________________________________________________ Much of the land adjacent to the tidal basin consists of swamp forests. Leaching of dissolved organic material from the swamp vegetation produces the darkly-stained "blackwater" in the riverine areas. Because of the large forested areas, silviculture (timber harvesting and processing) is an important industry in the watershed. Timber harvest must be done with care, because when forested land is disturbed it creates a potential for pollutants to run off the land following rainstorms. This is especially true of clearcutting, which is removal of all trees in a given area. Additionally, some forestry operations spray herbicides on large areas of the landscape, which may present a problem to waters draining those areas. The largest human use of land in the watershed is devoted to crop agriculture, which represents about 24% of the land coverage. Again, agricultural operations must be performed with care to prevent unwanted materials to drain into nearby waterways. Agricultural operations utilize large amounts of fertilizers, which should be kept from groundwater and surface waters. The largest industry in the Black and Northeast Cape Fear River watersheds is industrialized livestock production. This is an industry in which hundreds to thousands of hogs, turkeys, or chickens are raised together in long buildings, which are termed concentrated animal feeding operations (CAFOs). These animals are fed by vast amounts of feed brought in by trainload from the Midwest. The urine and feces they generated is washed through slats in the floor to a system of pipes that carries the waste outside into a large pond called a waste lagoon. Periodically the CAFO operator pumps out some of the waste and sprays it on nearby fields (called sprayfields), which absorb some of the wastes. Approximately 5,000,000 of North Carolina's hogs are located in the Cape Fear basin. The Cape Fear watershed is the most heavily industrialized basin in North Carolina, with numerous industries utilizing the Cape Fear in the upper watershed and eleven major industrial dischargers in the tidal basin itself. There are 280 municipal and industrial wastewater discharges in the watershed which have permits to operate. Hence, there is considerable municipal, industrial, and agricultural water usage in the basin, much of which eventually enters the river as wastewater plant effluent or surface runoff. We will discuss the potential pollution impacts of human land use on the waters of the Cape Fear system below. FLORA
AND FAUNA - THE Living Resources The lower Cape Fear basin is extremely rich and diverse in both habitats and wildlife. The region at the mouth of the estuary contains abundant salt marsh and lowland swamp forest (Table 1), and sandy beaches (Bald Head Island is known as a major nesting area for sea turtles). The adjoining regions are drained by tidal creeks passing through a variety of land formations before reaching the estuary. Other natural regions surrounding the estuary also contain longleaf pine savannahs, old-growth forests, Carolina Bays, and lime sinks. The fresh-to-oligohaline tidal areas are notable in that they contain the only significant amount of tidal freshwater marsh in North Carolina. There are 27 species on the North Carolina Protected Plant list that are thought to occur in the river basin. This diverse natural habitat is home to a rich assemblage of wildlife. Approximately 42 mammal, 197 bird, and 57 reptile and amphibian species occur in this area of North Carolina. The lower Cape Fear is part of the Atlantic Coast flyway for migratory waterfowl. Numerous bird species utilize the tidal creeks, dredge spoil islands, sandy beaches, salt and freshwater marshes, swamps, and nearby uplands forests either as homes or migratory stops. Several fur-bearing mammals are likewise dependent on the river and estuarine environment for survival. At least 22 threatened and endangered species are thought to utilize the varied habitats of the lower Cape Fear system. These include the red-cockaded woodpecker, the Southeast bald eagle, the shortnose sturgeon, the Eastern cougar, the American alligator, sea turtles, and even the occasional manatee. The estuary and freshwater tidal basin is very rich in terms of tidal creeks, salt and freshwater marshes. Numerous studies have documented the function of these areas as primary nursery areas for larval and juvenile fish. These areas are important both ecologically for fish in general and economically, because many commercial ly-fished species utilize these nursery areas. Good water quality is essential in these primary nursery areas to maintain fisheries productivity. The Cape Fear River and Estuary serves as a migratory route for several anadromous fish populations. These include sturgeon (including the endangered shortnose sturgeon), striped bass, American shad, and herring, all of which were historically fished commercially. Habitat degradation and migratory route impediments have caused either closing or reductions of these once-important fisheries. POLLUTION PROBLEMS AND SOURCES IN THE CAPE FEAR There are two types of water pollution: point source and non-point source. Point sources are those that come out of a pipe. Most major point sources are regulated by state and Federal agencies. They are permitted to discharge a given amount of polluting substances into streams at rates that the agencies think will not by unduly harmful to the environment. These sources are relatively easy to sample. Non-point sources are materials washed into water bodies by rainfall runoff. They are much harder to sample and control. What are the major pollution problems in the Cape Fear River system? Low dissolved oxygen is a widespread problem, particularly in summer. Low dissolved oxygen stresses fish and other aquatic organisms, and can lead to kills if levels fall too far. One of the factors causing low dissolved oxygen is biochemical oxygen demand (BOD). BOD-causing materials include human sewage, animal manure, wood pulp, and debris from forest clearcutting and everyday forest functioning. The large amounts of swamp drainage that enters the rivers tends to produce water that is naturally low in dissolved oxygen; thus, the river and estuary become particularly sensitive to any further man-made BOD inputs. Another widespread problem is contamination of streams and rivers by bacteria, viruses, and protozoans, collectively called microbes. Some of these microbes are pathogenic (cause disease), so scientists to determine the safety of the water must estimate their abundances. Typically scientists measure fecal coliform bacteria to determine water safety. Sources of fecal coliform bacteria are improperly treated human sewage, runoff from hog and poultry farms, pet manure, and wild animal manure. Turbidity is any kind of material, organic or inorganic, that clouds the water. A major type of turbidity is dirt, especially clay that runs off the land during and after a rainstorm. This occurs where there has been land-disturbing activity, such as timber cutting, agriculture, road building, or most types of new construction. Increased turbidity can reduce visibility for sight-feeding fish, and reduce numbers or diversity of benthic prey items. Turbidity can also adsorb various other pollutants such as fecal coliforms and nutrients and carry then large distances downstream. The best way to prevent turbidity in the water is to provide a 30 to 100 ft vegetated buffer zone along streams and runoff ditches. Another useful practice is to direct non-point source runoff into wet detention ponds. These are small lakes created to trap pollutants before they enter the water. Nutrients that pollute the water consist mainly of nitrogen and phosphorus. Nutrient come from both point and non-point sources, including sewage treatment plants, CAFOs, crop fields, lawns and gardens, and pet manure. These nutrients will fertilize the algae in lakes and streams, and can cause algal blooms and stimulate toxic dinoflagellates such as Pfiesteria. An important source of pollution in the Cape Fear basin is accidents, runoff, and illegal pumping of materials from CAFOs. In 1995 several major hog and poultry lagoon breaches and leaks occurred, releasing large quantities of nutrients, BOD, fecal bacteria and turbidity into nearby waterways. These incidents have occurred periodically since then in the Cape Fear and other river basins. Fish kills and algal blooms have occurred as a result of these situations. The Cape Fear has also experienced microbial and nutrient pollution from poorly functioning sewage treatment plants. Regarding forestry, there have been clearcuts with too small a buffer zone left along the streambank, that have polluted the water with BOD, nutrients, and fecal bacteria. And over all, some poorly planned urban and suburban development activities have led to runoff pollution of nutrients, turbidity, and fecal bacteria. Thus there are many types of pollution that impact the waters of the Cape Fear River system. SAMPLING
THE CAPE FEAR Water quality in the Cape Fear River system is currently being sampled more intensely than ever before. The sampling effort is being carried out by the Lower Cape Fear River Program (LCFRP), which is overseen and advised by a coalition of local municipalities, streamside industries, environmental groups, and regulatory agencies. Its website is: http://www.uncwil.edu/cmsr/aquaticecology/lcfrp/. The water sampling and data analysis is performed by the University of North Carolina at Wilmington's Aquatic Ecology laboratory, located at the Center for Marine Science: http://www.uncwil.edu/cmsr/aquaticecology/laboratory/. We sample ten river and estuary stations by boat, and another 25 stations are streams sampled from the shore. The water quality effort samples water temperature, salinity, turbidity, dissolved oxygen, pH, light, suspended solids, nutrients, chlorophyll, fecal coliform bacteria, and metals. Another part of the sampling effort is centered on the benthos, which are organisms living on or near the stream bottom. This effort is carried out by the UNCW Benthic Ecology Laboratory: http://www.uncwil.edu/cmsr/benthic/. The final element of the sampling program is a fisheries sampling effort, also carried out by researchers from the UNCW Center for Marine Science. HOW
WEATHER AFFECTS THE WATER AND ITS QUALITY Rainfall is an important factor controlling the ecology and pollution of the Cape Fear River system. Rainfall controls river flow. In summer, it is somewhat less of a factor because the green vegetation takes up rainwater and transpires it back into the atmosphere. However, in winter there is little evaporation and transpiration, so rainfall runs directly into streams and rivers, greatly increasing river flow. In both cases, however, rainfall upstream carries non-point source pollution into tributary streams of the Cape Fear, and river flow carries these pollutants downstream. Research by the LCFRP has demonstrated that sharp increases in nitrogen and phosphorus in the Cape Fear Estuary are preceded by rainfall in the Piedmont by about two weeks. In tributary watersheds of the Cape Fear, LCFRP research has shown that rain causes sharp increases in turbidity and fecal coliform bacteria in nearby streams within one day. However, the same research also showed that watersheds that had large wetlands coverage did not see those sharp increases. In these cases the wetlands absorbed the rainfall runoff and associated pollutants before they could enter the streams. HURRICANES
- THE BIG WEATHER IMPACT Hurricanes have struck the Cape Fear area repeatedly since 1995. Atmospheric scientists tell us that we are in a cycle that will continue to generate high numbers of hurricanes and tropical storms for the next few decades. We have learned some scientific lessons from previous hurricanes that directly concern the environment. Hurricanes have major impacts on water quality. When a hurricane hits, usually one of the first things to happen is the electric power shutting down. When this happens, sewage treatment plants and pumping stations cannot do their job. Untreated or partially treated human sewage is then rerouted directly into the rivers or tributary streams. This occurred during hurricanes Fran, Bonnie, and Floyd. Inside of cities, sewer lines will overflow because of the huge amounts of rainfall. This load of human sewage carries with it bacteria and other harmful microbes, BOD, and nutrients. Another major problem concerns hog farms on river floodplains. The heavy rains cause some waste lagoons to breach, others to overflow, and some become entirely inundated by floodwaters. This adds vast quantities of bacteria, BOD, and nutrients to the rivers. In some cases CAFO operators pumped waste from lagoons directly onto rain-saturated fields so the lagoon itself would not overflow. However, data collected by the LCFRP showed that this pumping had the same effect as direct overflows of waste - it lead to high BOD and bacterial counts in the river where it passed through areas of intense waste pumping. Additionally, thousands of hogs turkeys, and chickens were drowned in CAFOs flooded after hurricane Floyd. The high BOD load to the system from human, hog, and poultry waste led to large decreases in river dissolved oxygen, causing massive fish kills. Finally, there were pollution problems caused by septic systems that were flooded. These were associated with houses that were located on river floodplains. Thus, it is clear that development of river floodplains for human housing or industrial livestock production has a high potential for pollution when major storms hit. We cannot stop hurricanes from coming. However, we can do a better job of protecting water quality from their effects. One critical factor is to have independent backup generators for all sewage treatment plants, so that when the main power fails the plants can continue operations. Since Hurricane Fran many plants have acquired such backup systems; however, others still lack them. Another obvious way to improve water quality is to keep CAFOs off of river floodplains, thus removing an important source of pollution from a high-risk area. WHAT DOES THE FUTURE HOLD? Changes in water quality, such as increased turbidity due to runoff, or worsening dissolved oxygen from increased organic loading into the system, threaten the system's living resources. Lowered dissolved oxygen will pose further barriers to anadromous fish species that utilize the Cape Fear river as a migratory route to upstream spawning grounds. Increases in microbial pollution from hog farms and increased development close shellfishing beds for sport and commercial fishermen. Less fish and shellfish for sport and commercial fishermen affects the economic base of the region, in which fishing and tourism has played a major role. Scientific
Reference Materials Website for the Lower Cape Fear River Program -contains annual reports and data: http://www.uncwil.edu/cmsr/aquaticecology/lcfrp/ Bricker, S.B., C.G. Clement, D.E. Pirhalla, S.P. Orlando and D.R.G.
Farrow. 1999. National
Estuarine Eutrophication Assessment: Effects of Nutrient Enrichment
in the Nation’s Estuaries. NOAA, National Ocean Service, Special
Projects Office and the National Centers for Coastal Ocean Science. Silver
Spring, MD, 71 pp. Cahoon, L.B., J.A. Mickucki and M.A. Mallin. 1999. Nutrient imports to the Cape Fear and Neuse River basins to support animal production. Environmental Science and Technology 33:410-415. Dame, R., M. Alber, D. Allen, A. Chalmers, R. Gardner, C. Gilman, B. Kjerfve, A. Lewitus, M. Mallin, C. Montague, J. Pinckney and N. Smith. 2000. Estuaries of the south Atlantic coast of North America: Their geographical signatures. Estuaries 23:793-819. Ensign, S.E. and M.A. Mallin. 2001. Stream water quality following timber harvest in a Coastal Plain swamp forest. Water Research 35:3381-3390. Mallin, M.A., L.B. Cahoon, D.C. Parsons and S.H. Ensign. 2001. Effect of nitrogen and phosphorus loading on plankton in Coastal Plain blackwater streams. Journal of Freshwater Ecology 16:455-466. Mallin, M.A., J.M. Burkholder, L.B. Cahoon and M.H. Posey. 2000. The North and South Carolina coasts. Marine Pollution Bulletin 41:56-75. Mallin, M.A. 2000. Impacts of industrial-scale swine and poultry production on rivers and estuaries. American Scientist 88:26-37. Mallin, M.A., L.B. Cahoon, M.R. McIver, D.C. Parsons and G.C. Shank. 1999. Alternation of factors limiting phytoplankton production in the Cape Fear Estuary. Estuaries 22:985-996. Mallin, M.A., M.H. Posey, G.C. Shank, M.R. McIver, S.H. Ensign and T.D. Alphin. 1999. Hurricane effects on water quality and benthos in the Cape Fear Watershed: Natural and anthropogenic impacts. Ecological Applications 9:350-362. National Oceanic & Atmospheric Administration (NOAA). 1996. NOAA’s Estuarine Eutrophication Survey, Volume 1: South Atlantic Region. NOAA, Office of Ocean Resources Conservation Assessment, Silver Spring, MD, 50 pp. North Carolina Department of Natural Resources and Community Development (NCDNRCD). 1983. Status of Water Resources, Cape Fear River Basin Study 1981-1983. Raleigh, N.C. North Carolina Division of Water Quality (NCDWQ). 2000. Cape Fear River Basinwide Water Quality Plan. NC Department of Environment and Natural Resources, Water Quality Section, 1617 Mail Service Center, Raleigh, NC 27699-1617. Definitions estuary – This is the region where freshwater and salt water from the ocean mix. It is generally defined as the salinity region from full strength marine water (about 35 parts per thousand, or ppt) down to about 0.5 ppt at the upper end of the estuary.
Piedmont - This is a geographical region characterized by gently rolling hills and clay soils. It runs from the NC mountains to the “fall line”, that marks the break between the Piedmont and coastal Plain. The fall line is roughly 90 miles from the coast.
Coastal Plain – this is the region between the Piedmont and ocean, a broad, sandy, gently sloping plain originally containing swampy forests and blackwater streams. Now this region is home to intense agricultural activities and high urbanization near the coast.
blackwater - Blackwater is a term used for streams and lakes that lie on the Coastal Plain that are stained a dark, tea-like color. The stain comes from organic acids that leach from swamp vegetation, and is harmless to humans and animals.
primary nursery areas - These are fresh or brackish shallow water habitats that contain aquatic plants. Larval and juvenile stages of many species of fish find food and protection from predators in these habitats, and spend part of their life cycle in them.
permitted – The State of North Carolina is allowed to issue discharge permits to point sources through the National Pollutant Discharge Elimination System (NPDES), which is overseen by the United States Environmental Protection agency.
dissolved oxygen – The dissolved oxygen standard for protection of aquatic life in North Carolina waters is 5 ppm (parts per million), also called mg/L (milligrams per liter). In swamp water the standard is reduced to 4 ppm. Generally waters with 2 ppm or less of dissolved oxygen will kill fish or drive them away.
biochemical oxygen demand – BOD is a measure of the organic material in the water that is fed on by aquatic bacteria. During normal respiration bacteria take up dissolved oxygen as part of their metabolism. When there is a spill of sewage or hog waste this greatly increases the BOD of the water, which causes rapid increases in bacteria, which then use up the dissolved oxygen in the water.
fecal coliform bacteria – These bacteria reside in the intestines of warm-blooded animals, and are used to estimate the potential danger from disease causing microbes. Regulations state that safe shellfishing waters have less than 14 per 100 ml of water, and waters for human contact have less than 200 per 100 ml of water.
turbidity - Turbidity is measured in Nephelometric Turbidity Units (NTUs). The State of North Carolina has a freshwater standard of 50 NTUs and a brackish water standard of 25 NTU to protect water quality.
Dinoflagellates - Dinoflagellates are microscopic organisms that can survive in a number of different ways. Most can photosynthesize like other algae; some can eat microscopic organisms, others can absorb particulate or dissolved materials, and some can use all or some of these techniques to survive. Several dinoflagellates can to toxic to humans and other organisms.
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