@article{johnson_burchell_evans_osmond_gilliam_2013, title={Riparian buffer located in an upland landscape position does not enhance nitrate-nitrogen removal}, volume={52}, ISSN={0925-8574}, url={http://dx.doi.org/10.1016/j.ecoleng.2012.11.006}, DOI={10.1016/j.ecoleng.2012.11.006}, abstractNote={Relatively narrow (<50 m) riparian buffers strategically reestablished in correct landscape positions have been shown to significantly reduce agricultural non-point source pollution to streams. Because of this, conservation programs have been established to encourage landowners to enroll lands near surface waters to improve water quality. Former cropland enrolled in a conservation program was evaluated to determine its effectiveness in reducing nitrate-nitrogen (NO3−-N) in shallow groundwater. This conservation buffer (CB) was up to 80 m wide and was planted with loblolly pine (Pinus taeda). It was situated upslope of an existing 30–60 m wide riparian hardwood forest buffer (EHB) located within the floodplain of an intermittent stream. Shallow groundwater NO3−-N, groundwater hydrology, total organic carbon, and soil redox potential were measured throughout both the CB and the EHB for 18 months. Groundwater NO3−-N concentrations, often 5–15 mg L−1 within the CB, were not significantly reduced from concentrations that entered from the agricultural field edge. However, a decrease in NO3−-N concentration was observed within the EHB (17–83%). The hydrology of the CB coupled with relatively low organic carbon contributed to a low denitrification potential and lack of NO3−-N reduction compared with the EHB. While the CB enrollment likely provided additional habitat benefits it did not appear to provide treatment of groundwater NO3−-N. It is our conclusion that landscape position is a more important defining variable for buffer site selection than buffer width if NO3−-N reduction is a primary goal.}, journal={Ecological Engineering}, publisher={Elsevier BV}, author={Johnson, Sara R. and Burchell, Michael R., II and Evans, Robert O. and Osmond, Deanna L. and Gilliam, J. Wendell}, year={2013}, month={Mar}, pages={252–261} }
 @article{skaggs_youssef_gilliam_evans_2010, title={Effect of controlled drainage on water and nitrogen balances in drained lands}, volume={53}, DOI={10.13031/2013.35810}, abstractNote={Field studies have shown that subsurface drainage systems can be managed to conserve water and reduce losses of nitrogen (N) to surface waters. The practice, called controlled drainage (CD) or drainage water management (DWM), is a viable alternative for reducing N loads from drained cropland, including millions of acres in the Midwest. This article reviews past studies on the effect of CD on drainage volumes and N losses for a wide range of soils and climatological conditions and uses simulations to examine mechanisms affecting the practice. Results published in the literature show that CD has reduced drainage volumes and N losses in drainage waters by 17% to over 80%, depending on soil properties, crops, drainage intensities, control strategies, and location. This study resulted in the following conclusions. CD reduces subsurface drainage and raises water tables, while increasing ET, seepage, and surface runoff. Seepage, which depends on soil properties and site conditions, is an important factor that often governs the effectiveness of CD. Experiments to determine the effect of CD on drainage volumes and N losses should be conducted on the field or watershed scale so that impacts of seepage are properly represented. Increases in ET in response to CD are important but are rarely greater than 10%. The effect of this increase in water use on drainage water loss is also less than 10% for most locations. CD reduces N losses in drainage water by about the same percentage as its effect on subsurface drainage volume in most cases. The effect of CD on N loss to surface waters depends on denitrification, both in the profile and in reduced zones along seepage paths. For soils that do not develop reduced zones, the effect of CD on N loss may be substantially less than its effect on drainage volume.}, number={6}, journal={Transactions of the ASABE}, author={Skaggs, R. W. and Youssef, M. A. and Gilliam, J. W. and Evans, R. O.}, year={2010}, pages={1843–1850} }
 @article{smith_osmond_moorman_stucky_gilliam_2008, title={Effect of vegetation management on bird habitat in Riparian buffer zones}, volume={7}, ISSN={["1938-5412"]}, DOI={10.1656/1528-7092(2008)7[277:EOVMOB]2.0.CO;2}, abstractNote={Abstract Riparian buffers can be valuable refuge areas for wildlife in otherwise homogeneous agricultural landscapes. Government sponsored programs like the Cropland Reserve Program generally require the planting of specific vegetative species during buffer restoration, although the effectiveness of such an approach when compared to restoration by volunteer species is unknown. We studied the effect of differences in vegetation structure on avian habitat in riparian buffer zones. A 25 m (82 ft) wide planted woodland buffer, 30 m (98 ft) wide grass, shrub, and woodland three-zone buffer, and a 9 m (30 ft) wide shrub buffer were evaluated for habitat potential using breeding-bird counts and vegetation surveys. Bird density and species richness varied with the structure of the vegetative communities present at the three sites. Avian species richness and total detections were higher in the three-zone buffer than in both the shrub and planted buffer, likely a result of the diversity of vegetation at the site. These data suggest that restoration of riparian areas by allowing fallow vegetation to recolonize is at the very least equally beneficial to avian wildlife as is restoration by planting specific grass, shrub, and tree species. Buffer restoration by natural revegetation using this method could be recommended as an alternative to implementation by planting riparian species due to its simplicity and cost effectiveness.}, number={2}, journal={SOUTHEASTERN NATURALIST}, author={Smith, Timothy A. and Osmond, Deanna L. and Moorman, Christopher E. and Stucky, Jon M. and Gilliam, J. Wendell}, year={2008}, pages={277–288} }
 @inproceedings{appelboom_chescheir_skaggs_gilliam_amatya_2008, title={Nitrogen balance for a plantation forest drainage canal on the North Carolina coastal plain}, volume={51}, DOI={10.13031/2013.25239}, abstractNote={Human alteration of the nitrogen cycle has led to increased riverine nitrogen loads, contributing to the eutrophication of lakes, streams, estuaries, and near-coastal oceans. These riverine nitrogen loads are usually less than the total nitrogen inputs to the system, indicating nitrogen removal during transport through the drainage network. A two-year monitoring study quantified the ammonium, nitrate, and organic-N inputs, outputs, and inferred in-stream processes responsible for nitrogen transformations and removal in a 1900 m reach of a drainage canal located in a managed pine plantation. Total nitrogen inputs to the canal section were 527.8 kg in 2001 and 1422.7 kg in 2002. Total nitrogen discharge at the outlet was 502 kg in 2001 and 1458 kg in 2002. The mass balance of nitrogen inputs and outputs indicated a loss of 25.8 kg (5.1%) of total nitrogen from the system in 2001, and a gain of 35.3 kg (2.4%) of total nitrogen to the system in 2002. Variability in the input and output estimates was high, especially for groundwater exchange. Different hydrologic and nitrogen inputs and outputs were identified and quantified, but measurement variability obscured any potential nitrogen removal from the system.}, number={4}, booktitle={Transactions of the ASABE}, author={Appelboom, T. W. and Chescheir, G. M. and Skaggs, R. W. and Gilliam, J. W. and Amatya, D. M.}, year={2008}, pages={1215–1233} }
 @article{birgand_skaggs_chescheir_gilliam_2007, title={Nitrogen Removal in Streams of Agricultural Catchments—A Literature Review}, volume={37}, ISSN={1064-3389 1547-6537}, url={http://dx.doi.org/10.1080/10643380600966426}, DOI={10.1080/10643380600966426}, abstractNote={Excess nutrient loads have been recognized to be the major cause of serious water quality problems recently encountered in many estuaries and coastal waters of the world. Agriculture has been recognized in many regions of the world to be the largest single source of nitrogen emissions to the aquatic environments, and best management practices have been proposed to reduce nutrient losses at the field edge. As a result, there is growing awareness that nutrient management must be handled at the watershed scale. However, the key to nutrient management at the watershed scale is the understanding and quantification of the fate of nutrients both at the field scale and after they enter the aquatic environment. There has been widespread evidence since the late 1970s that nitrogen can be removed from water during its downstream transport in watersheds or basins. Although this information is becoming crucial, no overview has been proposed, so far, to qualitatively as well as quantitatively summarize available information in the literature. For this reason, we propose a review on the biogeochemical processes involved in nitrogen removal in streams, the rates of removal reported, and the factors influencing those rates. Nitrogen removal rates in agricultural streams should be expected to vary between 350 and 1250 mg N m−2 day−1. Mass transfer coefficients (coefficient evaluating intrinsic ability of a stream to remove nitrogen) values in agricultural streams may vary between 0.07 and 0.25 m day−1, although these values correspond to values obtained from reach scale studies. Reviewing values obtained from different measurement scales has revealed that results from incubations or experiments performed in the laboratory clearly underestimate mass transfer coefficients compared to those reported at the reach scale, from severalfold to more than one order of magnitude. Nitrogen removal rates and efficiency in streams are the highest in the summer, and this is critical for receiving ecosystems, which are most sensitive to external inputs at this period of the year. Removal efficiency is the lowest in winter in temperate climates due to high flow and loading combined with lowest removal rates. In-stream processes, on an annual basis, may remove at the watershed scale as much as 10 to 70% of the total N load to the drainage network.}, number={5}, journal={Critical Reviews in Environmental Science and Technology}, publisher={Informa UK Limited}, author={Birgand, Françoisx and Skaggs, R. Wayne and Chescheir, George M. and Gilliam, J. Wendell}, year={2007}, month={Jun}, pages={381–487} }
 @article{youssef_skaggs_chescheir_gilliam_2006, title={Field evaluation of a model for predicting nitrogen losses from drained lands}, volume={35}, ISSN={["1537-2537"]}, DOI={10.2134/jeq2005.0249}, abstractNote={ABSTRACT}, number={6}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={Youssef, Mohamed A. and Skaggs, R. Wayne and Chescheir, George M. and Gilliam, J. Wendell}, year={2006}, pages={2026–2042} }
 @article{smith_osmond_gilliam_2006, title={Riparian buffer width and nitrate removat in a tagoon-effluent irrigated agricutturat area}, volume={61}, number={5}, journal={Journal of Soil & Water Conservation}, author={Smith, T. A. and Osmond, D. L. and Gilliam, J. W.}, year={2006}, pages={273–281} }
 @article{skaggs_youssef_chescheir_gilliam_2005, title={Effect of drainage intensity on nitrogen losses from drained lands}, volume={48}, DOI={10.13031/2013.20103}, abstractNote={Agricultural drainage is a primary source of excessive nitrogen (N) in surface waters, leading to significant water 
quality problems in streams and estuaries in many locations around the world. Although there have been only a few field 
studies of the effect of drain depth and spacing on N loss to surface waters, the data that exist indicate that N loss increases 
as subsurface drains are placed closer together. Some simulation model studies agree with these trends, others do not. 
Published field data from Indiana and North Carolina were plotted as a function of drainage intensity (DI), which was defined 
as the steady-state drainage rate when the water table at a point midway between the drains is coincident with the surface. 
Trends for NO3-N loss as a function of DI were similar for soils in the two states in spite of large differences in weather and 
soil conditions. These data indicated that the magnitude of NO3-N loss in drainage waters is strongly dependent on DI. 
Simulations were conducted to examine effects of drain depth, spacing, and soil properties on processes that affect NO3-N 
loss from drained soils. The use of DI explained or normalized the effect of these variables on some of the processes but not 
others. Results showed that, in addition to its effect on DI, drain depth appears to have a significant impact on NO3-N losses.}, number={6}, journal={Transactions of the ASAE}, author={Skaggs, R. W. and Youssef, M. A. and Chescheir, G. M. and Gilliam, J. W.}, year={2005}, pages={2169–2177} }
 @article{burchell_skaggs_chescheir_gilliam_arnold_2005, title={Shallow subsurface drains to reduce nitrate losses from drained agricultural lands}, volume={48}, DOI={10.13031/2013.18518}, abstractNote={Nitrate losses from subsurface drainage systems remain an important environmental concern. Data were collected 
from two drainage systems near Plymouth, North Carolina, to evaluate the effect of subsurface drain depth on nitrate-nitrogen 
(NO3 
--N) losses. Drains in plot 1 were 1.5 m deep and 25 m apart, and drains in plot 2 were 0.75 m deep and 12.5 m apart. 
Both plots received swine wastewater applications. Overall, the shallow drainage system had 42% less outflow than the 
deeper drainage system. Lower NO3 
--N concentrations were observed in the shallow groundwater beneath the shallow 
drainage plots as a result of higher water tables and likely increased denitrification. However, NO3 
--N concentrations in the 
drainage water from the shallow drains were not reduced. On average, NO3 
--N export from the shallow subsurface drains 
was 8 kg ha-1 in 2001 and 27 kg ha-1 in 2002. Nitrate export from the deeper drains was 6 kg ha-1 in 2001 and 37 kg ha-1 
in 2002. Decreased export observed in 2002 from the shallow subsurface drainage system was significant at the 10% level, 
but not for the entire 21-month period. Longer-term field studies, which incorporate variable climatological events, are 
needed to conclude whether shallower drain depth will reduce NO3 
--N export from subsurface drainage systems.}, number={3}, journal={Transactions of the ASAE}, author={Burchell, Michael and Skaggs, R. W. and Chescheir, G. M. and Gilliam, J. W. and Arnold, L. A.}, year={2005}, pages={1079–1089} }
 @article{youssef_skaggs_chescheir_gilliam_2005, title={The  nitrogen simulation model, DRAINMOD-N II}, volume={48}, DOI={10.13031/2013.18335}, abstractNote={DRAINMOD-N II is a field-scale, process-based model that was developed to simulate nitrogen dynamics and 
turnover in the soil-water-plant system under different management practices and soil and environmental conditions. It is 
an enhanced version of the nitrogen (N) simulation model, DRAINMOD-N, that simulates a more complete N cycle, adds a 
carbon (C) cycle, and operates at different levels of complexity. Processes considered in the model include atmospheric 
deposition, application of mineral N fertilizers including urea and anhydrous ammonia (NH3), soil amendment with organic 
N (ON) sources including plant residues and animal waste, plant uptake, organic C (OC) decomposition and associated N 
mineralization/immobilization, nitrification, denitrification, NH3 volatilization, and N losses via subsurface drainage and 
surface runoff. Nitrogen pools considered in the model are nitrate-nitrogen (NO3-N), ammoniacal nitrogen (NHx-N) and ON. 
DRAINMOD-N II includes a submodel that simulates C dynamics in the soil-plant system using a C cycle similar to that of 
the CENTURY model. A simplified approach is used to simulate temporal changes in soil pH; consequently, the model 
determines the composition of the NHx-N pool and, if necessary, changes its operation mode. DRAINMOD-N II simulates 
N reactive transport using a finite difference solution to a multiphase form of the one-dimensional advection- 
dispersion-reaction equation. Model output includes daily concentrations of NO3-N and NHx-N in soil solution and drain 
flow, daily OC content of the top 20 cm soil layer, and cumulative rates of simulated N processes.}, number={2}, journal={Transactions of the ASAE}, author={Youssef, M. A. and Skaggs, R. W. and Chescheir, G. M. and Gilliam, J. W.}, year={2005}, pages={611–626} }
 @article{amatya_chescheir_fernandez_skaggs_gilliam_2004, title={DRAINWAT-based methods for estimating nitrogen transport in poorly drained watersheds}, volume={47}, DOI={10.13031/2013.16100}, abstractNote={Methods are needed to quantify effects of land use and management practices on nutrient and sediment loads at 
the watershed scale. Two methods were used to apply a DRAINMOD-based watershed-scale model (DRAINWAT) to estimate 
total nitrogen (N) transport from a poorly drained, forested watershed. In both methods, in-stream retention or losses of N 
were calculated with a lumped-parameter model, which assumes that N concentration decreases exponentially with residence 
(or travel) time in the canals. In the first method, daily field outflows predicted by DRAINWAT were multiplied by average 
N concentrations to calculate daily loads at the field edge. Travel time from the field edge to the watershed outlet was computed 
for each field for each day based on daily velocities predicted by DRAINWAT for each section of the canal-stream network. 
The second lumped-parameter method was similar but used predicted annual outflow to obtain annual load at the field 
edge. The load was transported to the watershed outlet, and the in-stream N loss was determined by using a constant average 
velocity (obtained by long-term DRAINWAT simulations), independent of season, for the entire canal-stream network. The 
methods were applied on a 2,950 ha coastal forested watershed near Plymouth, North Carolina, to evaluate daily, monthly, 
and annual export of nitrogen for a five-year (1996-2000) period. Except for some late spring and hurricane events, predicted 
daily flows were in good agreement with measured results for all five years (Nash-Sutcliffe coefficient, E = 0.71 to 0.85). 
Estimates of monthly total N load were in much better agreement (E = 0.76) with measured data than were the daily estimates 
(E = 0.19). Annual nitrogen load was predicted within 17% of the measured value, on average, and there was no difference 
(. = 0.05) between measured and estimated monthly and annual loads. The estimates of annual N loads using travel time with 
a daily velocity yielded better results than with the constant average velocity. The estimated delivery ratio (load at the 
outlet/load at the field edge) for total N was shown to vary widely among individual fields depending on their location in the 
watershed and distance from the outlet. Both of the methods investigated can potentially be used with GIS in predicting 
impacts of land management practices on total N loads from poorly drained watersheds.}, number={3}, journal={Transactions of the ASAE}, author={Amatya, D. M. and Chescheir, G. M. and Fernandez, G. P. and Skaggs, R. W. and Gilliam, J. W.}, year={2004}, pages={677–687} }
 @article{amatya_skaggs_gilliam_hughes_2003, title={Effects of orifice-weir outlet on hydrology and water quality of a drained forested watershed}, volume={27}, number={2}, journal={Southern Journal of Applied Forestry}, author={Amatya, D. M. and Skaggs, R. W. and Gilliam, J. W. and Hughes, J. H.}, year={2003}, pages={130–142} }
 @book{chescheir_lebo_amatya_hughes_gilliam_skaggs_herrmann_2003, title={Hydrology and water quality of forested lands in eastern North Carolina}, publisher={Raleigh, N.C. : N.C. Agricultural Research Service, N.C. State University}, author={Chescheir, G. M. and Lebo, M. E. and Amatya, D. M. and Hughes, J. and Gilliam, J. W. and Skaggs, R. W. and Herrmann, R. B.}, year={2003} }
 @article{dukes_evans_gilliam_kunickis_2003, title={Interactive effects of controlled drainage and riparian buffers on shallow groundwater qaulity}, volume={129}, DOI={10.1061/(ASCE)0733-9437(2003)129:2(82)}, abstractNote={As a result of recent surface water quality problems in North Carolina, riparian buffers and controlled drainage are being used to reduce the loss of nonpoint source nitrogen from agricultural fields. The effect of controlled drainage and riparian buffers as best management practices to reduce the loss of agricultural nonpoint source nitrogen from the middle coastal plain has not been well documented. The middle coastal plain is characterized by intensive agriculture on sandy soils with deeply incised or channelized streams. A 2-year study was conducted to determine the effectiveness of controlled drainage, riparian buffers, and a combination of both in the middle coastal plain of North Carolina. It was hypothesized that raising the water table near the ditch would enhance nitrate-nitrogen reduction through denitrification. On the sandy soils studied, controlled drainage did not effectively raise the water table near the ditch to a greater degree than observed on the free drainage treatment. Due to random treatment location, the free drainage treatment was installed along a ditch with a shallower impermeable layer compared to the impermeable layer on the controlled drainage treatments (2 m versus 3- to 4-m deep). This resulted in a perched or higher water table on the free drainage treatment. Over 17 storm events, the riparian buffer (free drainage) treatment had an average groundwater table depth of 0.92 m compared to 0.96 and 1.45 m for the combination (riparian buffer and controlled drainage) and controlled drainage treatments, respectively. Nitrate concentration decrease between the field wells and ditch edge wells averaged 29% (buffer only), 63% (buffer and controlled drainage), and 73% (controlled drainage only). Although apparently more nitrate was removed from the groundwater on the controlled drainage treatments, the controlled drainage treatment water table near the ditch was not raised closer to the ground surface compared to the free drainage treatment. Nitrate removal effectiveness was attributed to local soil and landscape properties, such as denitrification in deeper reduced zones of the soil profile.}, number={2}, journal={Journal of Irrigation and Drainage Engineering}, author={Dukes, M. D. and Evans, R. O. and Gilliam, J. W. and Kunickis, S. H.}, year={2003}, pages={82–92} }
 @article{dukes_evans_gilliam_kunickis_2002, title={Effect of riparian buffer width and vegetation type on shallow groundwater quality in the Middle Coastal Plain of North Carolina}, volume={45}, DOI={10.13031/2013.8528}, abstractNote={The effect of riparian buffer width and vegetation type on shallow groundwater quality has not been evaluated 
in the Middle Coastal Plain of North Carolina. Four riparian buffer vegetation types and no–buffer (no–till corn and rye 
rotation or pasture) were established at 8 and 15 m widths as follows: cool season grass (fescue), deep–rooted grass (switch 
grass), forest (pine and mixed hardwood), and native vegetation. Nested groundwater monitoring wells were installed at the 
field/buffer edge and the stream edge in the middle of each riparian buffer plot at three depths. Most deep, mid–depth, and 
shallow wells were 3.0 m, 1.8 m, and 0.6 m deep from the ground surface to the top of the 0.6 m perforated section, respectively. 
Wells were sampled for 23 months beginning July 1998. Although the ditch well nitrate–nitrogen concentrations at the middle 
well depth were significantly lower in the 15 m wide plots compared to the 8 m plots over half the monitoring period, extreme 
flooding as a result of a hurricane in the middle of the study confounded the results. The effect of vegetation was not significant 
at any time, including the no–buffer cropped and fertilized plots. The effect of vegetation was minimized because at the early 
stage in the buffer vegetation establishment, vegetative cover and root mass were not fully developed, the hurricane–induced 
flooding forced the re–establishment of several vegetation types (forest and fescue), and there was likely some mixing of 
groundwater flowing toward the vegetation plots. Establishment of buffers along streams where groundwater flowed away 
from the stream did not result in lower groundwater nitrate levels.}, number={2}, journal={Transactions of the ASAE}, author={Dukes, M. D. and Evans, R. O. and Gilliam, J. W. and Kunickis, S. H.}, year={2002}, pages={327–336} }
 @article{leytem_mikkelsen_gilliam_2002, title={Sorption of organic phosphorus compounds in Atlantic coastal plain soils}, volume={167}, DOI={10.1097/01.ss0000034854.98442.39}, number={10}, journal={Soil Science}, author={Leytem, A. B. and Mikkelsen, R. L. and Gilliam, J. W.}, year={2002}, pages={652–658} }
 @article{mitsch_day_gilliam_groffman_hey_randall_wang_2001, title={Reducing nitrogen loading to the Gulf of Mexico from the Mississippi River Basin: Strategies to counter a persistent ecological problem}, volume={51}, ISSN={["1525-3244"]}, DOI={10.1641/0006-3568(2001)051[0373:RNLTTG]2.0.CO;2}, abstractNote={S and rivers themselves are not always much affected by nutrient loading. However, in most cases these nutrient-enriched waterways flow to the sea, with eutrophication of coastal waters the unfortunate result. This problem now occurs regularly throughout the world, in locations such as the Gulf of Mexico (Rabalais et al. 1999), the Baltic Sea (Larson et al. 1985), the Adriatic Sea (Faganeli et al. 1985), and the Black Sea (Tolmazin 1985). But we have moved beyond being concerned about nutrients only in the regions where they are discharged to being concerned about their movement through large watersheds (thousands and even millions of square kilometers in extent) and over long distances (hundreds to thousands of kilometers), and their effects on large areas of coastal water. In this article we describe a suite of practices that, if effected collectively, could help reduce nitrogen loadings to the Gulf of Mexico. These practices, in turn, could help limit hypoxia (the presence of low levels of dissolved oxygen in bottom waters, generally less than 2 mg per L) on the continental shelf of the northern Gulf of Mexico, a seasonally severe problem that has persisted there for the past decade. Between 1993 and 1999 the hypoxia zone ranged in extent from 13,000 to 20,000 km2 (Rabalais et al. 1996, 1998, 1999, Rabalais and Turner 2001). The hypoxia is most widespread, persistent, and severe in June, July, and August, although its extent and timing can vary, in part because of the amplitude and timing of flow and subsequent nutrient loading from the Mississippi River Basin. The waters that discharge to the Gulf of Mexico originate in the watersheds of the Mississippi, Ohio, and Missouri Rivers (collectively described here as the Mississippi River Basin). With a total watershed of 3 million km2, this basin encompasses about 40% of the territory of the lower 48 states (Figure 1) and accounts for 90% of the freshwater inflow to}, number={5}, journal={BIOSCIENCE}, author={Mitsch, WJ and Day, JW and Gilliam, JW and Groffman, PM and Hey, DL and Randall, GW and Wang, NM}, year={2001}, month={May}, pages={373–388} }
 @article{karr_showers_gilliam_andres_2001, title={Tracing nitrate transport and environmental impact from intensive swine farming using delta nitrogen-15}, volume={30}, ISSN={["1537-2537"]}, DOI={10.2134/jeq2001.3041163x}, abstractNote={ABSTRACT}, number={4}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={Karr, JD and Showers, WJ and Gilliam, JW and Andres, AS}, year={2001}, pages={1163–1175} }
 @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} }
 @inproceedings{birgand_chescheir_skaggs_gilliam_1999, title={Quantification and effects of in-stream processes in the ditches and canals of the Lower Coastal Plain of North Carolina}, number={1999}, booktitle={Proceedings of the Mini-Conference, Advances in Water Quality Modeling}, publisher={St. Joseph, MI: ASAE}, author={Birgand, F. and Chescheir, G. M. and Skaggs, R. W. and Gilliam, J. W.}, year={1999}, pages={45–50} }
 @article{verchot_franklin_gilliam_1998, title={Effects of agricultural runoff dispersion on nitrate reduction in forested filter zone soils}, volume={62}, ISSN={["0361-5995"]}, DOI={10.2136/sssaj1998.03615995006200060033x}, abstractNote={Abstract}, number={6}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Verchot, LV and Franklin, EC and Gilliam, JW}, year={1998}, pages={1719–1724} }
 @article{amatya_gilliam_skaggs_lebo_campbell_1998, title={Effects of controlled drainage on forest water quality}, volume={27}, ISSN={["0047-2425"]}, DOI={10.2134/jeq1998.00472425002700040029x}, abstractNote={Abstract}, number={4}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={Amatya, DM and Gilliam, JW and Skaggs, RW and Lebo, ME and Campbell, RG}, year={1998}, pages={923–935} }
 @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={Abstract}, 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={Abstract}, 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{verchot_franklin_gilliam_1997, title={Nitrogen cycling in piedmont vegetated filter zones .1. Surface soil processes}, volume={26}, ISSN={["0047-2425"]}, DOI={10.2134/jeq1997.00472425002600020002x}, abstractNote={Abstract}, number={2}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={Verchot, LV and Franklin, EC and Gilliam, JW}, year={1997}, pages={327–336} }
 @article{verchot_franklin_gilliam_1997, title={Nitrogen cycling in piedmont vegetated filter zones .2. Subsurface nitrate removal}, volume={26}, ISSN={["0047-2425"]}, DOI={10.2134/jeq1997.00472425002600020003x}, abstractNote={Abstract}, number={2}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={Verchot, LV and Franklin, EC and Gilliam, JW}, year={1997}, pages={337–347} }
 @article{lowrance_altier_newbold_schnabel_groffman_denver_correll_gilliam_robinson_brinsfield_et al._1997, title={Water quality functions of Riparian forest buffers in Chesapeake Bay watersheds}, volume={21}, ISSN={["1432-1009"]}, DOI={10.1007/s002679900060}, abstractNote={/ Maryland, Virginia, and Pennsylvania, USA, have agreed to reduce nutrient loadings to Chesapeake Bay by 40% by the year 2000. This requires control of nonpoint sources of nutrients, much of which comes from agriculture. Riparian forest buffer systems (RFBS) provide effective control of nonpoint source (NPS) pollution in some types of agricultural watersheds. Control of NPS pollution is dependent on the type of pollutant and the hydrologic connection between pollution sources, the RFBS, and the stream. Water quality improvements are most likely in areas of where most of the excess precipitation moves across, in, or near the root zone of the RFBS. In areas such as the Inner Coastal Plain and Piedmont watersheds with thin soils, RFBS should retain 50%-90% of the total loading of nitrate in shallow groundwater, sediment in surface runoff, and total N in both surface runoff and groundwater. Retention of phosphorus is generally much less. In regions with deeper soils and/or greater regional groundwater recharge (such as parts of the Piedmont and the Valley and Ridge), RFBS water quality improvements are probably much less. The expected levels of pollutant control by RFBS are identified for each of nine physiographic provinces of the Chesapeake Bay Watershed. Issues related to of establishment, sustainability, and management are also discussed.KEY WORDS: Riparian forest buffers; Chesapeake Bay; Nonpoint source pollution; Nitrogen; Phosphorus; Sediment}, number={5}, journal={ENVIRONMENTAL MANAGEMENT}, author={Lowrance, R and Altier, LS and Newbold, JD and Schnabel, RR and Groffman, PM and Denver, JM and Correll, DL and Gilliam, JW and Robinson, JL and Brinsfield, RB and et al.}, year={1997}, pages={687–712} }
 @article{gilliam_1994, title={RIPARIAN WETLANDS AND WATER-QUALITY}, volume={23}, ISSN={["0047-2425"]}, DOI={10.2134/jeq1994.00472425002300050007x}, abstractNote={Because of wet soils adjacent to the streams, riparian buffers are frequently present between farming and urban activities on the uplands and small streams. These riparian areas have been shown to be very valuable for the removal of nonpoint-source pollution from drainage water. Several researchers have measured >90% reductions in sediment and nitrate concentrations in water flowing through the riparian areas. The riparian buffers are less effective for P removal but may retain 50% of the surface-water P entering them. I consider riparian buffers to be the most important factor influencing nonpoint-source pollutants entering surface water in many areas of the USA and the most important wetlands for surface water quality protection.}, number={5}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={GILLIAM, JW}, year={1994}, pages={896–900} }
 @article{gilliam_schipper_beets_mcconchie_1992, title={Riparian buffers in New Zealand forestry}, volume={37}, number={2}, journal={New Zealand Forestry}, author={Gilliam, J. W. and Schipper, L. A. and Beets, P. N. and McConchie, M.}, year={1992}, pages={21} }
 @article{gilliam_cassel_daniels_stone_1985, title={Interrelationships among soil erosion, landscape position and soil productivity in the North Carolina Piedmont}, ISBN={9780916150693}, journal={Erosion and soil productivity}, publisher={St. Joseph, Mich.: American Society of Agricultural Engineers}, author={Gilliam, J. W. and Cassel, D. K. and Daniels, R. B. and Stone, J. R.}, year={1985}, pages={75} }
 @article{jacobs_gilliam_1985, title={RIPARIAN LOSSES OF NITRATE FROM AGRICULTURAL DRAINAGE WATERS}, volume={14}, ISSN={["0047-2425"]}, DOI={10.2134/jeq1985.00472425001400040004x}, abstractNote={Abstract}, number={4}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={JACOBS, TC and GILLIAM, JW}, year={1985}, pages={472–478} }
 @inbook{gilliam_skaggs_1981, title={Drainage and agricultural development: Effects on drainage waters}, ISBN={0879334185}, booktitle={Pocosin wetlands: an integrated analysis of coastal plain freshwater bogs in North Carolina}, publisher={Stroudsburg, Pennsylvania: Hutchinson Ross Publishing Company}, author={Gilliam, J. W. and Skaggs, R. W.}, editor={C. J. Richardson, L. Matthews and Anderson, S. A.Editors}, year={1981}, pages={198} }