@article{nelson_parsons_2006, title={Modification and validation of GLEAMS for prediction of phosphorus leaching in waste-amended soils}, volume={49}, DOI={10.13031/2013.22055}, abstractNote={Excess phosphorus applied to soils with low P adsorption capacities can enter surface water via leaching and subsurface transport, thereby negatively impacting water quality. Computer simulation models can be used to describe the effects of management practices on P leaching losses, provided the models are appropriately validated. The objectives of this research were to modify and validate P subroutines in the GLEAMS (Groundwater Loading Effects of Agricultural Management Systems) model to more accurately reflect P sorption and desorption, and then use the modified model to determine crop and waste management effects on long-term P leaching losses below the root zone of a grazed pasture with >20-year history of swine lagoon liquid application and considerable P buildup in the soil profile. GLEAMS was modified with the Langmuir equation to partition labile P between adsorbed and solution phases. The modification improved predictions of percolate P concentrations and soil P accumulation in acid sandy soils receiving waste-based P additions. The modification also increased model sensitivity to changes in crop and P management. The modified model predicted that P-based swine lagoon liquid applications would decrease P leaching by >20 kg ha-1 year-1 compared to N-based applications. Eliminating all P applications decreased the predicted P leaching losses by less than 1 kg ha-1 year-1 compared to P-based swine lagoon liquid application. Results show that P can continue leaching from P-saturated soils even in the absence of P additions.}, number={5}, journal={Transactions of the ASABE}, author={Nelson, N. O. and Parsons, J. E.}, year={2006}, pages={1395–1407} }
 @article{nelson_parsons_mikkelsen_2005, title={Field-scale evaluation of phosphorus leaching in acid sandy soils receiving swine waste}, volume={34}, ISSN={["1537-2537"]}, DOI={10.2134/jeq2004.0445}, abstractNote={Accurate descriptions of P leaching are important because excess P applied to soils can enter surface water via leaching and subsurface transport, thereby negatively impacting water quality. The objectives of this study were to monitor P leaching in soils with a long-term history of waste application, relate soil solution P concentrations to soil P status, and quantify P leaching losses. Soil solution was monitored for 20 mo with samplers installed at 45-, 90-, and 135-cm depths in two pits (1 x 3 x 1.5 m) in Autryville (loamy, siliceous, thermic Arenic Paleudults) and Blanton (loamy, siliceous, semiactive, thermic Grossarenic Paleudults) soils located in a grazed pasture in Sampson County, NC, which had received swine waste for >20 yr. Maximum soil solution P concentrations at 45 cm exceeded 18 mg L(-1) in both soils. Soil solution P concentrations at 90 cm in the Blanton soil were similar to that at 45 cm indicating low P sorption. Soil solution P concentrations at 90 cm in the Autryville soil averaged 0.05 mg L(-1) compared to 10 mg L(-1) at 45 cm. A split-line model related soil solution P concentration to the degree of phosphorus saturation (DPS), identifying a change point at 45% DPS. Phosphorus movement past 45 cm equaled or exceeded surplus P additions for both soils. Long-term waste applications resulted in DPS > 90%, high soil solution P concentrations, and substantial vertical P movement. Phosphorus leaching should be considered when assessing long-term risk of P loss from waste-amended soils.}, number={6}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={Nelson, NO and Parsons, JE and Mikkelsen, RL}, year={2005}, pages={2024–2035} }
 @article{munoz-carpena_parsons_2004, title={A  design procedure for vegetative filter strips using VFSMOD-W}, volume={47}, number={6}, journal={Transactions of the ASAE}, author={Munoz-Carpena, R. and Parsons, J. E.}, year={2004}, pages={1933–1941} }
 @article{groundwater nitrate depletion in a swine lagoon effluent-irrigated pasture and adjacent riparian zone_1999, volume={54}, number={4}, journal={Journal of Soil & Water Conservation}, year={1999}, pages={651–656} }
 @article{munoz-carpena_parsons_gilliam_1999, title={Modeling hydrology and sediment transport in vegetative filter strips}, volume={214}, ISSN={["0022-1694"]}, DOI={10.1016/S0022-1694(98)00272-8}, abstractNote={The performance of vegetative filter strips is governed by complex mechanisms. Models can help simulate the field conditions and predict the buffer effectiveness. A single event model for simulating the hydrology and sediment filtration in buffer strips is developed and field tested. Input parameters, sensitivity analysis, calibration and field testing of the model are presented. The model was developed by linking three submodels to describe the principal mechanisms found in natural buffers: a Petrov–Galerkin finite element kinematic wave overland flow submodel, a modified Green–Ampt infiltration submodel and the University of Kentucky sediment filtration model for grass areas. The new formulation effectively handles complex sets of inputs similar to those found in natural events. Major outputs of the model are water outflow and sediment trapping on the strip. The strength of the model is a good description of the hydrology within the filter area, which is essential for achieving good sediment outflow predictions or trapping efficiency. The sensitivity analysis indicates that the most sensitive parameters for the hydrology component are initial soil water content and vertical saturated hydraulic conductivity, and sediment characteristics (particle size, fall velocity and sediment density) and grass spacing for the sediment component. A set of 27 natural runoff events (rainfall amounts from 0.003 to 0.03 m) from a North Carolina Piedmont site was used to test the hydrology component, and a subset of nine events for the sediment component. Good predictions are obtained with the model if shallow uniform sheet flow (no channelization) occurs within the filter.}, number={1-4}, journal={JOURNAL OF HYDROLOGY}, author={Munoz-Carpena, R and Parsons, JE and Gilliam, JW}, year={1999}, month={Jan}, pages={111–129} }
 @inproceedings{gilliam_parsons_mikkelsen_1999, title={Nitrogen dynamics and buffer zones}, number={1999}, booktitle={Buffer zones: Their processes and potential in water protection: The proceedings of the International Conference on Buffer Zones}, author={Gilliam, J. W. and Parsons, J. E. and Mikkelsen, R. L.}, year={1999}, pages={54–61} }
 @article{przepiora_hesterberg_parsons_gilliam_cassel_faircloth_1998, title={Field evaluation of calcium sulfate as a chemical flocculant for sedimentation basins}, volume={27}, ISSN={["0047-2425"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0032076630&partnerID=MN8TOARS}, DOI={10.2134/jeq1998.00472425002700030026x}, abstractNote={Sedimentation basins are built at construction sites to reduce the load of suspended solids in runoff water discharged into surface waters. However, these basins are not effective in reducing turbidity caused by fine suspended particles such as clay and silt. The objective of this field study was to evaluate the efficiency of moulding plaster (CaSO 4 . 0.5 H 2 O) as a chemical flocculant for reducing the turbidity of water discharged from sedimentation basins equipped with a floating skimmer device. Following each of 14 rainfall events, sedimentation basins at two urban construction sites were either treated with moulding plaster or left untreated, and the turbidity and chemical properties of the impounded water and discharge water were monitored as the basins drained during a 50- to 70-h time period. Each sedimentation basin was equipped with a floating skimmer device that discharged water at a controlled rate from 5-cm below the surface of the impounded water. The turbidity of discharge water from untreated basins ranged from 100 to 1650 NTU (nephelometric turbidity units), while a surface-applied moulding plaster treatment of 450 to 520 mg L -1 decreased the turbidity to <50 NTU. The time required for the discharge water from treated basins to reach either 100 NTU (2-20 h) or 50 NTU (5-52 h) was inversely proportional to the concentration of dissolved moulding plaster. Chemical flocculation using moulding plaster reduced the turbidity of discharge water to <50 NTU while producing dissolved SO 4 concentrations of <250 mg L -1 .}, number={3}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={Przepiora, A and Hesterberg, D and Parsons, JE and Gilliam, JW and Cassel, DK and Faircloth, W}, year={1998}, pages={669–678} }
 @inproceedings{parsons_gilliam_mikkelsen_1998, title={Stream water level control to enhance riparian buffer effectiveness removing nitrate-nitrogen}, booktitle={Drainage in the 21st century: Food production and the environment: Proceedings of the seventh International Drainage Symposium}, publisher={St. Joseph, Michigan: American Society of Agricultural Engineers}, author={Parsons, J. E. and Gilliam, J. W. and Mikkelsen, R. L.}, year={1998}, pages={551–558} }
 @article{breve_skaggs_parsons_gilliam_1998, title={Using the DRAINMOD-N model to study effects of drainage system design and management on crop productivity, profitability and NO3-N losses in drainage water}, volume={35}, ISSN={["1873-2283"]}, DOI={10.1016/S0378-3774(97)00035-8}, abstractNote={The environmental impacts of agricultural drainage have become a critical issue. There is a need to design and manage drainage and related water table control systems to satisfy both crop production and water quality objectives. The model DRAINMOD-N was used to study long-term effects of drainage system design and management on crop production, profitability, and nitrogen losses in two poorly drained soils typical of eastern North Carolina (NC), USA. Simulations were conducted for a 20-yr period (1971–1990) of continuous corn production at Plymouth, NC. The design scenarios evaluated consisted of three drain depths (0.75, 1.0, and 1.25 m), ten drain spacings (10, 15, 20, 25, 30, 40, 50, 60, 80, and 100 m), and two surface conditions (0.5 and 2.5 cm depressional storage). The management treatments included conventional drainage, controlled drainage during the summer season and controlled drainage during both the summer and winter seasons. Maximum profits for both soils were predicted for a 1.25 m drain depth and poor surface drainage (2.5 cm depressional storage). The optimum spacings were 40 and 20 m for the Portsmouth and Tomotley soils, respectively. These systems however would not be optimum from the water quality perspective. If the water quality objective is of equal importance to the productivity objective, the drainage systems need to be designed and managed to reduce NO3–N losses while still providing an acceptable profit from the crop. Simulated results showed NO3–N losses can be substantially reduced by decreasing drain depth, improving surface drainage, and using controlled drainage. Within this context, NO3–N losses can be reduced by providing only the minimum subsurface drainage intensity required for production, by designing drainage systems to fit soil properties, and by using controlled drainage during periods when maximum drainage is not needed for production. The simulation results have demonstrated the applicability of DRAINMOD-N for quantifying effects of drainage design and management combinations on profits from agricultural crops and on losses of NO3–N to the environment for specific crop, soil and climatic conditions. Thus, the model can be used to guide design and management decisions for satisfying both productivity and environmental objectives and assessing the costs and benefits of alternative choices to each set of objectives.}, number={3}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Breve, MA and Skaggs, RW and Parsons, JE and Gilliam, JW}, year={1998}, month={Jan}, pages={227–243} }
 @article{przepiora_hesterberg_parsons_gilliam_cassel_faircloth_1997, title={Calcium sulfate as a flocculant to reduce sedimentation basin water turbidity}, volume={26}, ISSN={["0047-2425"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0031278959&partnerID=MN8TOARS}, DOI={10.2134/jeq1997.00472425002600060021x}, abstractNote={A high-suspended solids load in surface waters is one of the biggest water quality problems in the Piedmont region of the southeastern USA. Sedimentation basins at construction sites are designed to reduce suspended solids in discharged water, but they are not effective in reducing turbidity. A survey of sedimentation basin water at two urban construction sites showed that turbidity levels during a 9- to 12-mo period were always greater than the 50-NTU (nephelometric turbidity units) standard adopted in North Carolina for surface waters. Furthermore, water chemistry varied over time, with pH ranging from 5.8 to 8.9 and electrical conductivity (EC) ranging from 3.0 to 23.0 mS m -1 . Laboratory experiments demonstrated that temporal variations in the water chemistry were likely caused by contact with concrete and crushed stone. Laboratory flocculation experiments were completed to evaluate the efficiency of calcium sulfate compounds (hemihydrate, agricultural gypsum, and phosphogypsum) as chemical flocculants for reducing the turbidity of sedimentation basin water from two field sites and for different pH conditions. Moulding plaster (hemihydrate) was a more efficient flocculant than agricultural gypsum and has fewer environmental restrictions on its use than phosphogypsum. Moulding plaster application rates of 350 to 700 mg L -1 were needed to reduce the turbidity of unstirred sedimentation basin water to 50 NTU within 3 h after addition of the flocculant. To achieve a given turbidity level, less flocculant was required for longer flocculation and settling times, or when sedimentation basin water had a lower pH.}, number={6}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={Przepiora, A and Hesterberg, D and Parsons, JE and Gilliam, JW and Cassel, DK and Faircloth, W}, year={1997}, pages={1605–1611} }
 @article{breve_skaggs_parsons_gilliam_1997, title={DRAINMOD-N, a nitrogen model for artificially drained soils}, volume={40}, DOI={10.13031/2013.21359}, abstractNote={DRAINMOD-N, a quasi two-dimensional model that simulates the movement and fate of nitrogen in shallow 
water table soils with artificial drainage, is described. Results of sensitivity analyses are presented and model predictions 
are compared with results from VS2DNT, a more complex, two-dimensional model. The nitrogen transport component is 
based on an explicit solution to the advective-dispersive-reactive (ADR) equation. Nitrate-nitrogen is the main N pool 
considered. Functional relationships are used to quantify rainfall deposition, fertilizer dissolution, net mineralization, 
denitrification, plant uptake, and surface runoff and subsurface drainage losses. 
A sensitivity analysis showed DRAINMOD-N predictions are most sensitive to the standard rate coefficients for 
denitrification and mineralization and nitrogen content in rainfall. Simulated daily water table depths were within 
0.121 m, cumulative subsurface drainage rates were within 0.016 m, and cumulative surface runoff rates were within 
0.003 m, of those predicted by VS2DNT for a 250-day period. DRAINMOD-N predictions for NO3-N losses in subsurface 
drainage water only differed from VS2DNT predictions by less than 2.6 kg ha–1. DRAINMOD-N predictions for 
denitrification were within 8%, for plant uptake were within 15%, and for net mineralization were within 26%, of those 
simulated by VS2DNT.}, number={4}, journal={Transactions of the ASAE}, author={Breve, M. A. and Skaggs, R. W. and Parsons, J. E. and Gilliam, J. W.}, year={1997}, pages={1067–1075} }
 @article{breve_skaggs_gilliam_parsons_mohammad_chescheir_evans_1997, title={Field testing of DRAINMOD-N}, volume={40}, DOI={10.13031/2013.21360}, abstractNote={This study was conducted to evaluate the performance of DRAINMOD-N, a nitrogen fate and transport model 
for artificially drained soils, based on a comparison between predicted and observed hydrologic and nitrogen variables 
for an experimental site in eastern North Carolina. The site consisted of six plots drained by subsurface drain tubes 
1.25 m deep and 23 m apart. Each plot was instrumented to measure water table depth, subsurface drainage, surface 
runoff and subirrigation rates. There were two replications of three water management treatments: conventional 
drainage, controlled drainage and subirrigation. Crops were winter wheat followed by soybean. Results showed the 
model did a good job in describing the hydrology of the site. On average the predicted daily water table depths were 
within 0.13 m of observed during the 14-month study period. Differences between predicted and observed cumulative 
subsurface drainage and surface runoff volumes were less than 0.10 and 0.09 m, respectively, for all treatments. 
Predictions for the movement and fate of nitrogen were also in good agreement with measured results. Simulated nitratenitrogen 
(NO3-N) losses in subsurface drainage water were within 1.5 kg/ha of the observed values for the 14-month 
period. Differences between simulated and observed total NO3-N losses (subsurface drainage plus surface runoff) were 
within 3.0 kg/ha. 
Results of this study indicated DRAINMOD-N could be used to simulate nitrogen losses in poorly drained soils with 
artificial drainage. The model, however, needs to be tested for longer periods of time and under different climatic 
conditions and soil types, before it can be recommended for general use.}, number={4}, journal={Transactions of the ASAE}, author={Breve, M. A. and Skaggs, R. W. and Gilliam, J. W. and Parsons, J E. and Mohammad, A. T. and Chescheir, G. M. and Evans, R. O.}, year={1997}, pages={1077–1085} }
 @article{parsons_gilliam_mikkelsen_1997, title={Modeling offsite water quality impacts of land applications of swine waste effluent}, number={972147}, journal={Paper (American Society of Agricultural Engineers)}, author={Parsons, J. E. and Gilliam, J. W. and Mikkelsen, R. L.}, year={1997}, pages={13} }
 @article{parsons_skaggs_doty_1990, title={SIMULATION OF CONTROLLED DRAINAGE IN OPEN-DITCH DRAINAGE SYSTEMS}, volume={18}, ISSN={["0378-3774"]}, DOI={10.1016/0378-3774(90)90013-O}, abstractNote={Subsurface water management was analyzed for a typical open-ditch drainage system in eastern North Carolina. The water management model, watrcom, was used to simulate conventional drainage, controlled drainage, and subirrigation for the 1982–1986 growing seasons. The effects of water management on drainage outflow, relative corn yields, and irrigation water requirements were analyzed. The effect of inflow from upstream uncontrolled drainage areas was also considered. During the dry years controlled drainage increased relative yields over conventional drainage; however, predicted yields were less than those obtained with subirrigation because of drought stresses. In 1984, rainfall exceeded pet and yields predicted for controlled drainage were similar to those obtained with subirrigation. Controlled drainage also decreased drainage outflows. Both average yields and yields midway between the drainage ditches were analyzed for all water management treatments. The relationship between yield and distance from the drain was dependent on hydraulic conductivity. Predicted yields for conventional drainage were higher at the midpoint than those near the ditch due primarily to drought. However, yields near the ditches tended to be higher than those at the midpoint for controlled drainage and subirrigation.}, number={4}, journal={AGRICULTURAL WATER MANAGEMENT}, author={PARSONS, JE and SKAGGS, RW and DOTY, CW}, year={1990}, month={Nov}, pages={301–316} }