Figure 1. Typical hydrologic cycle for eastern North Carolina
(from Evans et al., 1991). The Problem of Water Pollution in North Carolina
North Carolina is a state with abundant water resources. There are over 35,000 miles of
streams and rivers in North Carolina, as well as several of the largest estuaries in the
United States and 320 miles of coastal waters. The water resources in North Carolina most
affected by pollution are streams and rivers, followed by lakes and ponds. Only 40% of the
streams and rivers are fully supporting: this means that the streams and rivers meet their
designated uses such as swimming, fishing, and drinking (USEPA, 1995a). Approximately 75%
of the lakes and ponds and 95% of the estuaries are fully supporting.
Within the boundaries of the State of North Carolina there are 17 river basins: Broad, Cape Fear, Catawba, Chowan, French Broad, Hiwassee, Little Tennessee, Lumber, New, Neuse, Pasquotank, Roanoke, Savannah, Tar-Pamlico, Watauga, White Oak, and Yadkin. In general, the water quality of the river basins located in the mountains is high to very high, while the water quality of rivers that traverse the Piedmont and Coastal Plain is of lower quality. Stream and river water quality in some of the river basins is very high (Hiwassee, Little Tennessee, Savannah, and Watauga). However, water quality in the Cape Fear, Chowan, Lumber, Neuse, and Tar-Pamlico river basins is degraded by pollution.
The types of pollution vary: sediment, nutrients (nitrogen and phosphorus), bacteria
(fecal coliform), metals, organics (oil, grease, pesticides), and oxygen-reducing
materials. However, the pollutants of greatest concern are sediment and nutrients.
The sources of pollution are diverse, although the majority of the pollutants are
delivered from nonpoint sources (diffuse runoff) as opposed to point sources (e.g.,
wastewater treatment systems, factories). Of the nonpoint sources of pollution in the
United States, the U.S. Environmental Protection Agency (USEPA) (1995a) estimates that
agriculture contributes 53%, construction 10%, mining and other activities 13%,
miscellaneous sources 12%, and urban runoff 12% to the pollution load.
Pollutants of Concern and Their
Delivery
Sediment. Excessive sediment from
eroding cropland, overgrazed pasture, construction sites, and other activities impacts
water resources by reducing water resource storage; destroying fish and wildlife habitat;
and negatively affecting property values, recreational uses (boating, fishing, swimming),
commercial uses (drinking water supplies), and navigation (USEPA, 1989; Clark et al.,
1985).
Water erosion is the natural process of soil movement from higher areas to lower areas by the action of water flowing downhill. During a storm event, precipitation rates may be greater than infiltration rates, resulting in overland flow of water or runoff. This creates the potential for water erosion. Agricultural activities, such as soil cultivation and the destruction of vegetative cover, accelerate soil erosion (Hickman et al., 1994).
Water erosion is a combination of three processes: 1) detachment, 2) transport, and 3) deposition. Soil is detached by the energy of raindrop impact or the force of flowing water. Transport of soil occurs via flowing water and soil deposition occurs when water velocity slows and suspended soil particles settle (Hickman et al., 1994). Most soil deposition occurs on land, although some soil reaches water resources, where it negatively affects uses of the water resources.
Nutrients: Nitrogen and Phosphorus.Nutrients
(phosphorus or nitrogen) can enter water resources through and
and Phosphorus surface runoff either dissolved in the water or attached to soil particles.
Nitrogen and phosphorus can accelerate eutrophication of water resources resulting in
algal blooms, reduced transparency, undesirable shifts in algal and fish populations, and
even fish kills (Clark et al., 1985). Nonpoint source nitrogen and phosphorus originate
from agricultural activities, both row crop and animal operations, as well as urban
stormwater runoff. Phosphorus is delivered via overland flow into receiving water
resources, usually attached to soil particles. Organic forms of nitrogen, attached to
sediment or as part of organic matter, also enter surface waters through overland flow.
The majority of nonpoint source nitrogen that enters surface waters is transported through subsurface flows. Surface runoff water commonly contains low concentrations of nitrogen compared to ground water flows from fertilized fields (or lawns). Most nitrogen added to soils as commercial fertilizer or organic wastes is converted to nitrate-nitrogen, a mobile form of nitrogen that readily moves with soil water. As rainwater enters the soil and flows downward through the rooting zone, the nitrogen will be absorbed by growing plants or it will move into the shallow ground water. The movement of nitrogen into the ground water most often occurs during the winter when plants are not growing, but nitrate leaching can also occur in very wet periods during the spring or summer.
Once the nitrate-nitrogen moves below the water table and enters the
saturated zone, it will flow with the ground water. In upland areas, ground water tends to
move downward, driven by periodic rainfall events that recharge the ground water system.
As the ground water percolates downward, it frequently encounters discontinuous clay
lenses, which are found throughout the Coastal Plain. These lenses, or aquitards, transmit
water more slowly than the overlying sediments. Thus, once an aquitard is encountered, the
major portion of the nitrate-nitrogen laden water will move laterally, discharging into a
stream or ditch. However, some ground water will flow into a semi-confined aquifer beneath
the aquitard, either by transmission through the aquitard or by downward flow along the
discontinuous boundaries of the lens (Figure 1). Nitrate has not been found in aquifers
lying below these confining layers. Nitrate that is carried with the ground water
eventually discharges to a surface-water body. The amount of nitrate entering the surface
water can be reduced if the ground water flows through a riparian buffer or discharges
into a controlled drainage system (which will be discussed later). Nitrate in ground water
that passes through a riparian buffer may either be utilized by the riparian vegetation or
converted to a gas by the bacteria found in the organic matter deposited in the area.
Denitrification in riparian soils is an extremely important process for removing nitrate
from ground water flowing from fertilized fields.
Figure 1. Typical hydrologic cycle for eastern North Carolina
(from Evans et al., 1991).
High concentrations of nitrate in the ground water are problematic. A recent North Carolina study of 1719 drinking water wells found that 1.8% of the wells had nitrate-nitrogen levels at or above 10 mg L-1 or 10 ppm (Miner et al., 1996). The threshold for contaminated drinking water is 10 ppm nitrate-nitrogen. In infants, 10 ppm may cause Methemoglobinemia or Blue Baby Syndrome — a condition in which nitrite binds with hemoglobin, thus reducing the transport of oxygen to tissues. Asphyxia may occur. Approximately 20% of the wells sampled contained between 4 and 9 ppm nitrate-nitrogen (Miner et al., 1996). Nitrate-nitrogen concentrations were greater in wells in Coastal Plain counties, where 4.9% of the tested wells contained 10 ppm nitrate-nitrogen or higher.
The contamination trend by nitrate-nitrogen is consistent with national survey results. A recent USEPA national well water study found that 2.4% of rural private wells contained nitrate-nitrogen concentrations above 10 mg L-1 (USEPA, 1990).
Fecal Coliform. Fecal coliform contamination, caused by animal waste runoff, septic systems, and point discharges of water from wastewater treatment plants, frequently impacts water resources adversely. When health advisory levels for fecal coliform concentrations are exceeded, water resources are closed for body contact sport as well as harvesting of filter feeders (mussels, oysters). Currently, 18% of North Carolina’s shellfish beds are closed to harvesting due to fecal coliform contamination.
Most nonpoint sources of fecal coliform contamination are caused by overland flow. Runoff from areas of fecal deposition move into surface waters or sometimes even into drinking water wells if the wells are not constructed properly.
Pesticides. Some pesticides may
enter water resources through surface runoff, either dissolved in the water or attached to
soil particles. In addition, pesticides can be leached through the soil into the ground
water.
In North Carolina, Wade et al. (1997) found that 5 of 46 wells, or 12% of the drinking
water wells tested, were above Maximum Contaminant Levels for the pesticides tested. Three
of these pesticides are currently registered; two were formerly registered. Using ground
water data from eight states, Goodrich et al. (1991) found that 40% of the private rural
or farm wells sampled had pesticide detections. Pesticide contamination can affect biota
as well as contaminating drinking water supplies (Call et al., 1984).
Solutions: Best Management Practices
Point sources of pollution were regulated through federal legislation (The Clean Water
Act) in 1972. As a consequence, 60–80% of the pollution that now occurs in United
States waters comes from nonpoint sources (USEPA, 1995a). In order to reduce the impact of
nonpoint source pollution, changes in management must occur. Pollutants from nonpoint
sources can be controlled through the use of best management practices.
Best management practices (BMPs) are used to protect and conserve natural resources. Some BMPs are used to protect water resources, while other BMPs are implemented to protect wildlife habitat, both terrestrial and aquatic. Still other BMPs are utilized to protect land resources from degradation by wind, salt, and toxic levels of metals.
By controlling pollutants derived from agricultural or urban sources, BMPs can reduce or prevent impacts to the physical and biological integrity of surface and ground water and land resources.
Best management practices can be either structural (waste lagoons, terraces, sediment basins, or fencing) or managerial (rotational grazing, nutrient management, pesticide management, or conservation tillage). Both types of BMPs require good management to be effective in reducing agricultural nonpoint source pollution.
Best Management Practices:
How They Control
Transport of agricultural pollutants to surface and ground water can be controlled by
BMPs. Best management practices exert control by
Best Management Practices: Systems
The installation or use of one structural or management BMP is rarely sufficient to
control the pollutant of concern completely. Combinations of BMPs that control the same
pollutant are generally more effective than individual BMPs. These combinations, or
systems, of BMPs can be specifically tailored for particular agricultural and
environmental conditions, as well as for a particular pollutant (Osmond et al., 1995).
A BMP system is any combination of BMPs used together to comprehensively control a pollutant from the same source. When a pollutant originates from more than one source, a separate BMP system should be designed to reduce pollutant loss from each source. For example, if the problem is sediment from cropland, the BMP system to control field erosion would be different than if the sediment originated from cattle in the riparian buffer. To control sediment from livestock activities, fencing, revegetation of the riparian buffer, strategically located water troughs, and rotational grazing could be combined into a BMP system. The control of sediment from croplands could consist of many different techniques, including minimum tillage, strip cropping, field borders, and other practices.
An individual BMP can only control a pollutant at its source, during transport, or at the water’s edge. Systems of BMPs are generally more effective in controlling the pollutant since they can be used at two or more points in the pollutant delivery system. For example, in the Neuse River Basin, the current objective is to reduce the loss of nitrogen from cropland by 30%. A system of BMPs can be designed to reduce nitrogen at the source and during transport, as well as to remediate the nitrogen at the water’s edge. Nutrient management should be used to minimize nitrogen additions to surface and ground water (source reduction) but maintain yields. On average, only 40–60% of nitrogen fertilizer is used by crops. The remainder of the nitrogen becomes part of the soil organic matter, moves into the ground water, denitrifies (becomes gaseous nitrogen), or runs off with surface water. Field borders can be used to slow runoff from the field, thus decreasing transport of nitrogen by increasing movement of the nitrogen and water into the soil and increasing the absorption of the nitrogen by the field border crop. Nitrogen that is not controlled by nutrient management and field borders can be intercepted and remediated by riparian buffers along the water resource. Nitrate-nitrogen associated with ground water can be either denitrified by soil bacteria or absorbed by the riparian vegetation. Organic nitrogen, attached to soil particles flowing overland, can be trapped by the riparian vegetation. Used in conjunction as a system, these BMPs will reduce nitrogen loads into the Neuse River.
There is no single “ideal” BMP system to control a particular pollutant in all situations. Rather, the BMP system should be designed based on the
However, even properly designed systems of BMPs constitute only part of an effective land treatment strategy. In order for a land treatment strategy to be really effective, properly designed BMP systems must be placed in the correct locations in the watershed (critical areas) and the extent of land treatment must be sufficient to achieve water quality improvements (Line and Spooner, 1995). Generally, 75% of the critical area must be treated with the appropriate BMP systems. If the problem derives from livestock, generally 100% of the critical area within the watershed must be treated with BMP systems (Meals, 1993).
Purpose of the Manual
In 1988, the Environmental Management Commission (EMC) of North Carolina classified the
entire Neuse River Basin as Nutrient Sensitive Waters (NSW). That action, which allows
state government to control nutrient pollution that enters the river, was taken in
response to deteriorating water quality of the freshwater sections between Kinston and New
Bern. With this new nutrient management strategy, the EMC dealt with the control of
phosphorus and nitrogen in the Neuse River. The phosphorus detergent ban and controls on
point sources were successful — phosphorus loading to the Neuse decreased. However,
the problems persisted, especially below New Bern. In the summer and fall of 1995, fish
from New Bern to Minnesott Beach died by the millions due to low oxygen concentrations and
algal blooms. The Neuse is a nitrogen-limited system: excess nitrogen causes algal blooms
which in turn reduce oxygen levels below concentrations that support fish populations.
Scientists believe that in order to improve the health of the Neuse River, nitrogen loads need to be reduced by 30%. Reductions of nitrogen must occur from both point and nonpoint sources. The Division of Water Quality (DWQ) estimates that, at New Bern, agriculture contributes 54% of the nitrogen load; point sources, 24%; atmospheric, 3%; urban runoff, 6%; and forestry, 13%. Since the contribution of nitrogen from agricultural activities is significant, BMPs to reduce nitrogen contributions have been proposed.
It is expected that farmers in the Neuse River Basin will use a combination of BMPs to
reduce nitrogen loading of the Neuse. Animal operators have been mandated to implement the
.0200 rules by 1998, rules that prescribe the containment of animal waste and the disposal
of the waste at agronomic rates. For both livestock operators and row crop farmers, a
system of BMPs has been proposed that will consist of a combination of practices: nutrient
management, controlled drainage, riparian buffers, and stream practices. The system of
BMPs will always consist of nutrient management with one or more additional BMPs. For
example, farmers will be expected to use nutrient management and controlled drainage in
areas appropriate for controlled drainage. In other locations, producers may combine
riparian buffers and nutrient management, while at still other locations, controlled
drainage, in-stream constructed wetlands, and nutrient management will constitute the
appropriate BMP system.
In an attempt to customize the most effective system of BMPs to site-specific conditions,
a working group of the leading riparian buffer and controlled drainage specialists toured
riparian buffer and controlled drainage sites in the Piedmont and Coastal Plain of North
Carolina. As a result of their work, generalized site-specific systems of BMPs have been
proposed for particular regions. It must be remembered that the proposed site-specific
recommendations are the result of best professional judgment and as new data are acquired,
the proposals may change.
The purpose of this manual is to provide best professional guidance on the selection and placement of BMP systems that will reduce nitrogen loading from agriculture to the Neuse and other river basins in the Piedmont and Coastal Plain regions of North Carolina. Top of Page / Table of Contents / Next Section