INTRODUCTION

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 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
 

 
  • minimizing availability of pollutants; 
  •  retarding the transport and/or delivery of the pollutant, either by reducing water transported and thus the amount of the pollutant transported, or through deposition of the pollutant; or 
  • remediating or intercepting the pollutant before or after it is delivered to the water resource through chemical or biological transformation. 
Sediment
  • Sediment loss can be reduced by utilizing BMPs that minimize soil particle detachment. Practices that maintain crop residues or vegetative cover and improve soil properties, such as soil structure, organic matter and soil roughness, should be used. Conservation tillage practices are examples of BMPs that can reduce sediment loss.
  • Transport of sediment can be minimized by increasing crop residue or vegetative cover, reducing slope length and steepness, and slowing the movement of water. Terraces, field borders, grassed waterways, and contour cropping are BMPs used to slow the transport of sediment. 
  • Best management practices that intercept sediment and cause deposition reduce sediment delivery to water resources. Sediment basins, vegetative filter strips, and forested riparian buffers are examples of BMPs that intercept sediment by slowing the water velocity so that the sediment can settle out. 
Nutrients
  • Nutrient management is used to reduce nutrients transported to surface and ground water. Nutrient management includes matching nutrient application rates with crop needs, placing fertilizer correctly to optimize uptake, and timing fertilizer applications to meet the plants’ nutrient uptake capacity. For nutrients that are transported while attached to soil particles (phosphorus and some nitrogen species), BMPs that reduce sediment loss will also reduce nutrient loss.
  •  Best management practices that reduce the transport of nutrients include field borders, filter strips, and critical area plantings, including practices that slow runoff, such as contour farming and terraces and, in areas that are irrigated, irrigation management. 
  • Nutrients can be intercepted or transformed by using BMPs such as cover crops, riparian buffers, controlled drainage, or created in-stream wetlands. Cover crops may absorb residual nitrogen from deep in the soil profile, thus reducing leaching losses. Nitrate may be removed in riparian buffers through both denitrification and uptake, whereas organic nitrogen and phosphorus, attached to sediment, may be retarded by sediment deposition. 
Pesticides
  • Pesticides can be reduced by using crop management and integrated pest management techniques of applying pesticides only when needed: the proper type applied, at the correct rate and time. 
  • Transport of pesticides can be slowed by using the same type of BMPs that are employed to slow the transport of nutrients and sediment. 
  • Pesticides that are absorbed to soil particles can be intercepted using riparian buffers and sediment-intercepting BMPs such as sediment basins.

 
 

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