North Carolina Management System Evaluation Area

Kenansville site
Jun 1997

The North Carolina project is part of a national program entitled, "Agricultural Systems for Environmental Quality (ASEQ). It builds upon a 5-year USDA Water Quality Demonstration Project on the Herrings Marsh Run watershed near Kenansille in Duplin Co., North Carolina. The project area is typical of crop and livestock production with rapid growth occurring in the swine, poultry, cotton, and truck crop industries. The project involves Federal, State, and local agencies, farmers, private industries, commodity groups, and the general public.

Objectives and Results

Evaluate riparian strips and wetlands for nutrient reduction.


• Spray field: A historically overloaded swine wastewater spray field is being remediated by land expansion, improved wastewater application techniques, and rehabilitation of an adjacent wooded riparian zone. Ground- water monitoring wells (24) in the swine waste spray field and adjoining riparian zone have documented a decrease of the average nitrate-N concentration after the spray field was expanded. However, concentrations remain greater than 60 ppm. The soil of the spray field removed phosphorus (P) from the wastewater very effectively; low (less than 0.04 ppm) ortho-phosphate-p concentrations were found in both the ground and stream waters.

• Modeling: The GLEAMS model simulated the rise in nitrate-N concentration before the remediation activities, and the decrease in nitrate-N concentrations after their initiation. However, it simulated a slow recovery to safe drinking water levels.

• Rehabilitated wooded riparian zone: Five tree species were planted from the edge of the spray field to the stream bank (in sequence: green ash, red maple, sycamore, water oak, and bald cypress) to minimize the impact of surface and ground water outflows from the spray field. Nitrate-N concentrations decrease through the riparian zone, and stream concentrations at this site ranged from 12 to 14 ppm.

• Constructed in-stream wetland: A one-half acre in-stream wetland with a water level control structure is now operational below the restored wooded riparian zone. Measurements have been initiated for inflow and outflow volume, wetland depth, and N and P concentrations. Annual vegetation surveys are being conducted for composition, biomass, and nutrient accumulation. Annual sediment and sediment pore water sampling has begun.

• Enhanced in-stream wetland: Downstream, a second 1.3 acre wetland was constructed in an old pond with a breached dam. The wetland resulted in a decrease of outflow nitrate-N to less than 1 ppm during warmer months, while inflow nitrate-N has remained at 5 to 7 ppm. Chloride:nitrate ratios show that the reduction of nitrogen and phosphorous in the wetland is due to assimilation and transformation processes, not dilution.

Site-specific crop management as a best management practice.

• Yield mapping: Commercial equipment makes possible the customized applications of seed, fertilizer, and pesticide to specific parts of a field. This is particularly important in the SE Coastal Plain with its highly variable soils. Adoption of site-specific farming (SSF) technology is being encouraged by use of demonstration projects with farmer cooperators and commercial yield monitors. Delineating areas of high and low crop yield should increase adoption of SSF for optimizing field inputs, ultimately saving money and improving water quality.

Enhance efficiency of constructed wetlands to remove N and P from swine wastewater.

• Constructed wetlands: Disposal of wastewater generated by confined swine production can cause odor and water pollution problems. When farmland is limited, constructed wetlands can allow for safe disposal of lagoon effluents. Nitrogen removal efficiencies up to 70 percent were obtained using constructed wetlands planted to rush/bulrush or cattail/bur-reed plant mixtures with nitrogen application rates up to 15 pounds per acre daily. In a microcosm study, wetland plants grew vigorously with ammonia-N concentrations up to 240 ppm. However, conversion of ammonia to nitrate (nitrification) appears to be the limiting factor for N removal.

• Nitrification: Three technologies are being evaluated for their potential to enhance nitrification of lagoon wastewater. An overland flow treatment removed 59 percent of N applied at a 50 pounds per acre per day rate. A media filter treatment transformed up to 32 percent of the inflow total N into nitrate when wastewater was recycled four times. Immobilization of nitrifying microorganisms in polymer pellets resulted in faster nitrification rates and smaller reactors. The rate of nitrification with polyvinyl alcohol pellets is about 360 ppm of ammonia-nitrogen per day.

• Solid removal: Solids separation has the potential to reduce N treatment required. Polyacrylamide (PAM) is very effective for separating nutrients before the waste enters typical lagoon treatment. Low rates (25-100 ppm) can remove 80 percent of suspended solids, organic N, and organic P from flushing effluents. PAM treatment provides new alternatives for waste disposal. The solids can be composted, processed for refeeding, or transported to nutrient deficient cropland.

Technology transfer

• Decision support system: WATERSHEDSS is a decision support system that was developed through an EPA grant. Its purpose is to help managers determine appropriate systems and their placement on the landscape for particular water quality problems. Data collected on the effectiveness of the riparian and wetland systems will be included in a BMP database that is part of WATERSHEDSS.

• Workshops: Educational workshops led by NCSU extension personnel are presenting state-of-the-art information and facilitating technology transfer. The first was a Site-specific Farming Field Day in June 1996 at Goldsboro, NC. Future workshops include 1) Landscape features, 2) Constructed wetlands, and 3) Site-specific farming.

CONTACTS:
ARS - Patrick Hunt, 803-669-5203
NCSU - Frank Humenik, 919-515-6767
NRCS - George Stem, 919-873-2103