Open Grounds Farm

Located in Carteret County, NC. Open Grounds Farm is a 44,000 acre row crop operation which plants 13,000 acres of corn, 13,000 acres of soybean, and 4,000 acres of winter wheat, each year. A portion of the farm runoff drains into the South River, a tributary of the Neuse River estuary. The South River is approximately 13 km long and 2 meters deep, and exhibits estuarine circulation with an average salinity level of 12 ppt. The upper portion of the South River is bordered by irregularly flooded marsh (Juncus roemerianus).

Constructed Wetland

A wetland system was constructed to restore natural headwater hydrology and biological conditions with the goal of improving the water quality of runoff from the site. The wetland was designed to maximize nutrient and pathogen removal through plant uptake, sediment trapping, and enhancing microbial processes. The design includes 16 wetland cells alternating with adjacent ponds. The wetland cells were either planted with a monoculture of Spartina alterniflora, Cladium jamaicense, or Juncus roemarianus , or were left unplanted as controls. The perimeter of each wetland was planted with two rows of Spartina cynosuroides.

Water samples are collected on a bi-weekly basis at inflow points, outflow points, and within the constructed ponds. Temperature, DO, pH, and specific conductivity are also measured at each sampling location. Automated sampling is conducted on a flow-proportioned basis at inflow and outlet channels during runoff events. Water sample are analyzed for dissolved inorganic nutrients including nitrate, ammonia, phosphate, particulate organic carbon, hydrogen, nitrogen, and fecal coliforms. Seasonal plant nitrogen uptake is assessed through elemental analysis of carbon, nitrogen, and hydrogen (CHN) of representative plant tissue and measures of vegetation biomass in each wetland cell throughout the growing season. Sediments are sampled bi-weekly for CHN (nitrogen storage) and chlorophyll a content.

A membrane inlet mass spectrometer (MIMS) is used to measure denitrification in select wetland cells. Denitrification rates are compared between wetland cells planted with Juncus roemarianus and controls. Denitrification sampling focuses on factors that may influence denitrification, including benthic algal biomass, nutrient concentrations, organic carbon content, oxygen gradients, and vegetation species and biomass. Denitrification is quantified monthly and intensively during runoff events.

Contacts include Hans Paerl, Michael Piehler, Suzanne Thompson, and Amy Poe (UNC-CH Institute of Marine Sciences) for project management and N removal and design; G. Onorato (Open Grounds Farm) for buffer construction/design, Steve Broome (NCSU) for buffer planting/design, and Bill Kirby-Smith (Duke University Marine Lab) for sediment/pathogen removal.

Other research

Bill Kirby-Smith is also near the end of the first year of a three year project at Open Grounds Farm supported by the EPA 319 program through the NC DENR. They are sampling weekly at 14 stations in the upper south River (part impacted by the farm) repeating work done in the late 1970's and again in 1993-93. They are looking for differences in water quality that might be associated with the implementation of a number of BMP's. They are measuring salinity, temperature, turbidity, secchi, dissolved oxygen, nitrate+nitrite, amnmonia, phosphate, total suspended solids and chlorophyll A.