@article{moursi_youssef_poole_castro-bolinaga_chescheir_richardson_2023, title={Drainage water recycling reduced nitrogen, phosphorus, and sediment losses from a drained agricultural field in eastern North Carolina, USA}, volume={279}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2023.108179}, abstractNote={An experimental study was conducted to evaluate the effect of drainage water recycling (DWR) on reducing nitrogen (N), phosphorus (P), and sediment losses from agricultural fields to downstream surface water bodies. The two-year study (May 2019-April 2021) was conducted at an agricultural field in eastern North Carolina, U.S.A. A reservoir existed at the site was used to store subsurface drainage and surface runoff water during wet periods and provide supplemental irrigation during dry periods of the crop growing season. On average, the reservoir retained 14% of received inflow, with a higher flow reduction in the dry year (2019–2020; 29%) than the wet year (2020–2021; 8%). The hydraulic retention time (HRT) for the reservoir was 33.8 days for the dry year and 12.4 days for the wet year. The reservoir significantly reduced the loadings of N by 47%, P by 30% and sediment by 87%. Nitrogen load reduction was primarily driven by nitrate assimilation, the dominant form of N in the reservoir. Phosphorus load reduction was attributed to Orthophosphate assimilation as the reservoir released more particulate P than received. Reductions in both water flow and species concentration contributed to nutrient load reductions. Results suggested the removal efficiency of the reservoir would be highest during the summer and early fall months when the reservoir has a smaller water volume (due to irrigation), longer HRT, and warmer temperature. This study clearly demonstrated the potential of DWR for significantly reducing N, P, and sediment losses from agricultural land to receiving surface water. Further research is needed to investigate the physical, chemical, and biological processes that occur in the storage reservoir and affect the fate and transport of nutrients and sediment. The understanding of these processes will enable optimizing the treatment efficiency of DWR, which maximizes the system’s benefits and reduces construction cost.}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Moursi, Hossam and Youssef, Mohamed A. and Poole, Chad A. and Castro-Bolinaga, Celso F. and Chescheir, George M. and Richardson, Robert J.}, year={2023}, month={Apr} }
 @article{moursi_youssef_chescheir_2022, title={Development and application of DRAINMOD model for simulating crop yield and water conservation benefits of drainage water recycling}, volume={266}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2022.107592}, abstractNote={Drainage water recycling (DWR) is an emerging practice that has the potential to increase crop yield and improve water quality. DWR involves capturing and storing subsurface drainage water and surface runoff in ponds or reservoirs, and using this water for supplemental irrigation during dry periods of the growing season. The main objective of this study was to enhance DRAINMOD model to simulate the hydrology and crop yield of DWR systems. The expanded model; named DRAINMOD-DWR, has a new module that conducts a water balance of the storage reservoir and simulates the interaction between the reservoir and the field, irrigated from and/or draining into the reservoir. The model predicts the long-term performance of DWR as affected by weather conditions, soil type, crop rotation, reservoir size, and irrigation and drainage management. Three performance metrics were defined based on model predictions to quantify irrigation, crop yield, and water capture benefits of DWR. To demonstrate the new features of the model, uncalibrated DRAINMOD-DWR was applied to a hypothetical DWR system with continuous corn using a 50-yr (1970–2019) weather record in Eastern North Carolina, U.S. Different reservoir sizes were simulated to demonstrate how the model can predict the effect of storage capacity on the system’s performance. The model predicted that a 3.0-m deep reservoir with a surface area of 4% of the field area would optimize corn yield for the simulated conditions. The model application clearly demonstrated the DRAINMOD-DWR model’s capability of optimizing the DWR system design to avoid under-sizing or over-sizing the storage reservoir, which reduces system’s performance and increases implementation cost. Research is needed to test DRAINMOD-DWR using field measured data, and to develop routines for simulating the fate and transport of nutrients and sediment in the storage reservoir, which would enable the model to predict the water quality benefits of DWR.}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Moursi, Hossam and Youssef, Mohamed A. and Chescheir, George M.}, year={2022}, month={May} }
 @article{liu_tian_youssef_birgand_chescheir_2022, title={Patterns of long-term variations of nitrate concentration - Stream discharge relationships for a drained agricultural watershed in Mid-western USA}, volume={614}, ISSN={["1879-2707"]}, DOI={10.1016/j.jhydrol.2022.128479}, abstractNote={Nitrate Concentration–discharge (C-Q) relationships have been used to infer nitrate sources, storage, reactions, and transport in watersheds, and to reveal key processes that control runoff chemistry. Yet, studies on long-term nitrate C-Q relationships are limited due to scarce high frequency (e.g., daily) concentration data. In this paper, using a long-term high-frequency dataset (1976–2019) comprising stream flow and nitrate concentrations, we quantitatively analyzed the long-term variations of event-scale hysteresis patterns (quantified by hysteresis index, HI, and flushing index, FI) to infer the leaching mechanisms of nitrate in an artificially drained agricultural watershed in Mid-western U.S. Our results revealed that most events exhibited anti-clockwise behaviors (HI < 0), regardless of whether nitrate was flushed or diluted during events. This means that water with high levels of nitrate-N reaches the stream network slower than water with lower nitrate concentrations. Long-term mean FI was close to zero but had strong seasonal patterns with dilution patterns observed during Winter and Summer, and flushing patterns during late Spring and Fall. The consistently negative HI values regardless of the FI value gave a strong indication of the preponderant role of the near-drain zone that usually exhibits accelerated leaching and less accumulation of nitrate in the soil profile in these drained agricultural watersheds. Both HI and FI depicted strong but opposite seasonality because of weather patterns and agricultural activities, particularly N fertilization. Overall, our findings suggest a little evidence of the role of deep groundwater and instead a strong evidence of the role of subsurface drainage as the primary pathway for nitrate transport in drained agricultural watersheds. Therefore, artificial drainage could dampen N legacy caused by the historically intensive N fertilization in drained agricultural landscapes.}, journal={JOURNAL OF HYDROLOGY}, author={Liu, Wenlong and Tian, Shiying and Youssef, Mohamed A. and Birgand, Francois P. and Chescheir, George M.}, year={2022}, month={Nov} }
 @article{youssef_liu_chescheir_skaggs_negm_2021, title={DRAINMOD modeling framework for simulating controlled drainage effect on lateral seepage from artificially drained fields}, volume={254}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2021.106944}, abstractNote={We demonstrated a DRAINMOD modeling framework to predict controlled drainage (CD) effect on the fate of water in artificially drained agricultural fields, which is key for determining the water quality benefits of the practice. To demonstrate this modeling framework, DRAINMOD simulated the hydrology of a subsurface drained grass field in Eastern North Carolina, U.S. under both free drainage (FD) and CD. Three scenarios were simulated for each water management: no lateral seepage (LS) and LS with constant and dynamic hydraulic head (Hr). For each scenario, predicted water table depth (WTD) and subsurface drainage were compared to observed values using Mean Absolute Error, Nash-Sutcliffe Efficiency, and Normalized Percent Error. Predicted water balance components for different scenarios were also investigated. Results clearly showed that LS was a significant component of the water balance for CD. Model predictions showed that 96% of the reduction in subsurface drainage due to CD could be attributed to LS (33.5 cm yr−1). The large values of LS predicted by the model were attributed to the presence of a permeable sandy layer in the soil profile, the shallow management depth of the drain outlet, and the small size of the experimental field plots. Agreement between predicted and observed WTD and subsurface drainage ranged from acceptable to excellent for FD with and without considering LS. In contrast, DRAINMOD simulations for CD yielded acceptable predictions only for the scenario considering LS with dynamic Hr. This study demonstrated the power of process-based simulation models, such as DRAINMOD, for interpreting and explaining data of experimental studies and underscored the importance of using a proper model calibration strategy for yielding reliable predictions. This study highlights the need for well-coordinated experimental and modeling research to further investigate how seepage affect CD performance for reducing drainage flow and nitrogen losses from artificially drained agricultural fields.}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Youssef, Mohamed A. and Liu, Yu and Chescheir, George M. and Skaggs, R. Wayne and Negm, Lamyaa M.}, year={2021}, month={Aug} }
 @article{askar_youssef_vadas_hesterberg_amoozegar_chescheir_skaggs_2021, title={DRAINMOD-P: A MODEL FOR SIMULATING PHOSPHORUS DYNAMICS AND TRANSPORT IN DRAINED AGRICULTURAL LANDS: I. MODEL DEVELOPMENT}, volume={64}, ISSN={["2151-0040"]}, DOI={10.13031/trans.14509}, abstractNote={Highlights}, number={6}, journal={TRANSACTIONS OF THE ASABE}, author={Askar, Manal H. and Youssef, Mohamed A. and Vadas, Peter A. and Hesterberg, Dean L. and Amoozegar, Aziz and Chescheir, George M. and Skaggs, R. Wayne}, year={2021}, pages={1835–1847} }
 @article{askar_youssef_hesterberg_king_amoozegar_skaggs_chescheir_ghane_2021, title={DRAINMOD-P: A MODEL FOR SIMULATING PHOSPHORUS DYNAMICS AND TRANSPORT IN DRAINED AGRICULTURAL LANDS: II. MODEL TESTING}, volume={64}, ISSN={["2151-0040"]}, DOI={10.13031/trans.14510}, abstractNote={Highlights}, number={6}, journal={TRANSACTIONS OF THE ASABE}, author={Askar, Manal H. and Youssef, Mohamed A. and Hesterberg, Dean L. and King, Kevin W. and Amoozegar, Aziz and Skaggs, R. Wayne and Chescheir, George M. and Ghane, Ehsan}, year={2021}, pages={1849–1866} }
 @article{amatya_tian_marion_caldwell_laseter_youssef_grace_chescheir_panda_ouyang_et al._2021, title={Estimates of Precipitation IDF Curves and Design Discharges for Road-Crossing Drainage Structures: Case Study in Four Small Forested Watersheds in the Southeastern US}, volume={26}, ISSN={["1943-5584"]}, DOI={10.1061/(ASCE)HE.1943-5584.0002052}, abstractNote={AbstractWe compared precipitation intensity-duration-frequency (PIDF) curves developed for four small forested watersheds to spatially interpolated estimates from the National Oceanic and Atmospher...}, number={4}, journal={JOURNAL OF HYDROLOGIC ENGINEERING}, author={Amatya, D. M. and Tian, S. and Marion, D. A. and Caldwell, P. and Laseter, S. and Youssef, M. A. and Grace, J. M. and Chescheir, G. M. and Panda, S. and Ouyang, Y. and et al.}, year={2021}, month={Apr} }
 @article{askar_youssef_chescheir_negm_king_hesterberg_amoozegar_skaggs_2020, title={DRAINMOD Simulation of macropore flow at subsurface drained agricultural fields: Model modification and field testing}, volume={242}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2020.106401}, abstractNote={Macropores are critical pathways through which water and pollutants can bypass the soil matrix and be rapidly transported to subsurface drains and freshwater bodies. We modified the DRAINMOD model to simulate macropore flow using a simple approach as part of developing the DRAINMOD-P model to simulate phosphorus dynamics in artificially drained agricultural lands. The Hagen-Poiseuille's law was used to estimate the flow capacity of macropores. When ponding depths on the soil surface are greater than Kirkham's depth, water is assumed to flow through macropores directly to tile drains without interaction with the soil matrix. In the modified model, macropore size is adjusted based on wet or dry conditions while connectivity is altered by tillage. The model was tested using a 4-year data set from a subsurface drained field in northwest Ohio. The soils at the field are classified as very poorly drained and are prone to desiccation cracking. The modified model predicted the daily and monthly subsurface drainage with average Nash-Sutcliffe efficiency (NSE) values of 0.48 and 0.59, respectively. The cumulative drainage over the 4-year simulation period was under-predicted by 8%. The new macropore component was able to capture about 75% of 60 peak drainage flow events. However, surface runoff was over-predicted for the entire study period. Annual water budgets using measured data (precipitation, subsurface drainage, and surface runoff) and model predictions (evapotranspiration, vertical seepage, and change in storage) were not balanced with an average annual imbalance of 6.4 cm. The lack of closure in the water balance suggests that errors may have occurred in field measurements, particularly, surface runoff. Overall, incorporating macropore flow into DRAINMOD improved predictions of daily drainage peaks and enabled the model to predict subsurface drainage flux contributed by macropore flow, which is critical for expanding DRAINMOD to simulate phosphorus transport in subsurface drained agricultural land.}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Askar, Manal H. and Youssef, Mohamed A. and Chescheir, George M. and Negm, Lamyaa M. and King, Kevin W. and Hesterberg, Dean L. and Amoozegar, Aziz and Skaggs, R. Wayne}, year={2020}, month={Dec} }
 @article{skaggs_amatya_chescheir_2020, title={Effects of Drainage for Silviculture on Wetland Hydrology}, volume={40}, ISSN={["1943-6246"]}, DOI={10.1007/s13157-019-01202-6}, number={1}, journal={WETLANDS}, author={Skaggs, R. Wayne and Amatya, Devendra M. and Chescheir, George M.}, year={2020}, month={Feb}, pages={47–64} }
 @article{amatya_chescheir_williams_skaggs_tian_2020, title={Long-Term Water Table Dynamics of Forested Wetlands: Drivers and their Effects on Wetland Hydrology in The Southeastern Atlantic Coastal Plain}, volume={40}, ISSN={["1943-6246"]}, DOI={10.1007/s13157-019-01153-y}, number={1}, journal={WETLANDS}, author={Amatya, D. M. and Chescheir, M. and Williams, M. and Skaggs, W. and Tian, S.}, year={2020}, month={Feb}, pages={65–79} }
 @article{liu_youssef_birgand_chescheir_tian_maxwell_2020, title={Processes and mechanisms controlling nitrate dynamics in an artificially drained field: Insights from high-frequency water quality measurements}, volume={232}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2020.106032}, abstractNote={Intensive agricultural activities, especially in artificially drained agricultural landscapes, generate a considerable amount of nutrient export, which has been identified as a primary cause of water quality impairment. Several management practices have been developed and installed in agricultural watersheds to reduce nutrient export, e.g. nitrate-nitrogen (NO3-N). Although published research reported considerable water quality benefits of these practices, there exist many unanswered questions regarding the inherent processes and mechanisms that control nitrate fate and transport from drained agricultural landscape. To advance our understanding of processes and mechanisms, we deployed two high-frequency sampling systems in a drained agricultural field to investigate the relationship between agricultural drainage and nitrate concentrations (C-Q relationship). Results indicated that the high-frequency measuring system was able to capture the rapidly changing C-Q relationships at the experimental site, e.g. hysteresis patterns. The 22 identified storm events exhibited anti-clockwise behavior with high variability of flushing/dilution effects. In addition, high drainage flows contributed far more nitrate loading compared with lower flows. For instance, the top 10 % of drainage flow exported more than 50 % of the nitrate lost via subsurface drainage during the monitoring period. Additionally, we observed that animal waste application was the most influential practice to change the C-Q relationship by increasing the size of soil nitrogen pools. The insights obtained from the high-frequency water quality measurements could help provide practical suggestions regarding the design and management of conservation practices, such as controlled drainage, bioreactors, and saturated buffers, to improve their nitrogen removal efficiencies. This subsequently leads to better nutrient management in drained agricultural lands.}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Liu, Wenlong and Youssef, Mohamed A. and Birgand, Francois P. and Chescheir, George M. and Tian, Shiying and Maxwell, Bryan M.}, year={2020}, month={Apr} }
 @article{muwamba_amatya_chescheir_nettles_appelboom_tollner_ssegane_youssef_birgand_callahan_2020, title={Response of Drainage Water Quality to Fertilizer Applications on a Switchgrass Intercropped Coastal Pine Forest}, volume={12}, ISSN={["2073-4441"]}, DOI={10.3390/w12051265}, abstractNote={The objectives of this study were (1) to test the hypothesis that fertilizer applications do not increase nutrient fluxes on a switchgrass/pine forest (IC) when compared to a mature pine forest (MP) and (2) to evaluate post-fertilization (post-fert, 2014–2016) fluxes of nitrogen (N) and phosphorus (P) on IC and compare them to those observed during switchgrass growth prior to fertilization (pre-fert, 2012–2014) and site preparation for switchgrass establishment (site prep, 2009–2012). Nitrogen and P were applied to IC, a paired pure switchgrass site (SG), and MP, each about 25 ha in size, in June 2014, and again in June 2015 for the IC and SG sites only. Nitrogen and P concentrations were measured biweekly and rainfall and drainage outflow were measured continuously. During post-fert, the mean N concentrations and total loads were lower (p < 0.05) in IC than in SG and MP. The mean NO3-N concentration and loads in IC were lower during post-fert than during site prep. The post-fert phosphate concentrations in IC were lower than they were during pre-fert and site prep. Frequent N and P applications in IC did not significantly (α = 0.05) increase N and P fluxes, likely due to plant uptake and sorption on the acidic site.}, number={5}, journal={WATER}, author={Muwamba, Augustine and Amatya, Devendra M. and Chescheir, George M. and Nettles, Jamie E. and Appelboom, Timothy and Tollner, Ernest W. and Ssegane, Hebert and Youssef, Mohamed A. and Birgand, Francois and Callahan, Timothy}, year={2020}, month={May} }
 @article{muwamba_amatya_ssegane_chescheir_appelboom_nettles_tollner_youssef_walega_birgand_2020, title={Response of Nutrients and Sediment to Hydrologic Variables in Switchgrass Intercropped Pine Forest Ecosystems on Poorly Drained Soil}, volume={231}, ISSN={["1573-2932"]}, DOI={10.1007/s11270-020-04808-3}, number={9}, journal={WATER AIR AND SOIL POLLUTION}, author={Muwamba, Augustine and Amatya, Devendra M. and Ssegane, Herbert and Chescheir, George M. and Appelboom, Timothy and Nettles, Jamie E. and Tollner, Ernest W. and Youssef, Mohamed A. and Walega, Andrzej and Birgand, Francois}, year={2020}, month={Aug} }
 @article{negm_youssef_chescheir_skaggs_2019, title={DRAINMOD-based tools for quantifying reductions in annual drainage flow and nitrate losses resulting from drainage water management on croplands in eastern North Carolina (vol 166, pg 86, 2016)}, volume={226}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2019.105811}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Negm, L. M. and Youssef, M. A. and Chescheir, G. M. and Skaggs, R. W.}, year={2019}, month={Dec} }
 @article{maxwell_birgand_schipper_christianson_tian_helmers_williams_chescheir_youssef_2019, title={Drying–Rewetting Cycles Affect Nitrate Removal Rates in Woodchip Bioreactors}, volume={48}, ISSN={0047-2425}, url={http://dx.doi.org/10.2134/jeq2018.05.0199}, DOI={10.2134/jeq2018.05.0199}, abstractNote={Woodchip bioreactors are widely used to control nitrogen export from agriculture using denitrification. There is abundant evidence that drying–rewetting (DRW) cycles can promote enhanced metabolic rates in soils. A 287‐d experiment investigated the effects of weekly DRW cycles on nitrate (NO3) removal in woodchip columns in the laboratory receiving constant flow of nitrated water. Columns were exposed to continuous saturation (SAT) or to weekly, 8‐h drying‐rewetting (8 h of aerobiosis followed by saturation) cycles (DRW). Nitrate concentrations were measured at the column outlets every 2 h using novel multiplexed sampling methods coupled to spectrophotometric analysis. Drying–rewetting columns showed greater export of total and dissolved organic carbon and increased NO3 removal rates. Nitrate removal rates in DRW columns increased by up to 80%, relative to SAT columns, although DRW removal rates decreased quickly within 3 d after rewetting. Increased NO3 removal in DRW columns continued even after 39 DRW cycles, with ∼33% higher total NO3 mass removed over each weekly DRW cycle. Data collected in this experiment provide strong evidence that DRW cycles can dramatically improve NO3 removal in woodchip bioreactors, with carbon availability being a likely driver of improved efficiency. These results have implications for hydraulic management of woodchip bioreactors and other denitrification practices.}, number={1}, journal={Journal of Environment Quality}, publisher={American Society of Agronomy}, author={Maxwell, Bryan M. and Birgand, François and Schipper, Louis A. and Christianson, Laura E. and Tian, Shiying and Helmers, Matthew J. and Williams, David J. and Chescheir, George M. and Youssef, Mohamed A.}, year={2019}, pages={93} }
 @article{liu_youssef_chescheir_appelboom_poole_arellano_skaggs_2019, title={Effect of controlled drainage on nitrogen fate and transport for a subsurface drained grass field receiving liquid swine lagoon effluent}, volume={217}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2019.02.018}, abstractNote={Application of livestock manure has become a principal nutrient source in groundwater and surface water. The goal of this research was to investigate the effect of controlled drainage (CD) on nitrogen (N) fate and transport for a subsurface drained grass field receiving liquid swine lagoon effluent (SLE). A four-year field experiment was conducted on a naturally poorly drained pasture in eastern North Carolina. The 1.25 ha experimental field was artificially drained by subsurface drains installed at 1.0 m depth and 12.5 m spacing. Two treatments, replicated twice were implemented: conventional drainage (FD) and CD. The CD management protocol was more intensive compared to previous studies. The drain outlets of CD plot were set at 36 cm below soil surface all year round except several days before irrigation application when water table depth was shallower than 65 cm below surface. Controlled drainage significantly reduced drainage flow and TN loading via subsurface drain lines by an average of 397 mm yr−1 (93%) and 34.5 kg N ha−1 yr−1 (94%), respectively. DRAINMOD hydrologic simulations indicated that 96% of the reduction in predicted drain flow was attributed to increased lateral seepage. The nitrogen that did not drain from the field in response to CD was lost via enhanced denitrification (67%) and lateral seepage to adjacent fields (33%). This study clearly demonstrated how CD management affects the N fate and transport through seepage and denitrification process.}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Liu, Yu and Youssef, Mohamed A. and Chescheir, George M. and Appelboom, Timothy W. and Poole, Chad A. and Arellano, Consuelo and Skaggs, R. Wayne}, year={2019}, month={May}, pages={440–451} }
 @article{panda_amatya_muwamba_chescheir_2019, title={Estimation of evapotranspiration and its parameters for pine, switchgrass, and intercropping with remotely-sensed images based geospatial modeling}, volume={121}, ISSN={["1873-6726"]}, DOI={10.1016/j.envsoft.2019.07.012}, abstractNote={Intercropping switchgrass (Panicum virgatum) with pine can increase bioenergy feedstock production without land opportunity costs but can potentially alter water budgets. Measuring evapotranspiration (ET) and its parameters (stomatal conductance (gs), leaf area index (LAI), canopy temperature (Tc), and soil moisture (SM)) across cropping systems is costly and time-consuming. However, interpretation of remotely-sensed data can facilitate the effective assessment of relative ET demands among competing forest landuses. This study develops and tests geospatial models informed by a normalized difference vegetation index (NDVI), soil adjusted vegetation index (SAVI), vegetation vigor index (VVI), and other spectral information to estimate ET and its parameters, which are measured on experimental watersheds with young pines and natural understory (YP), switchgrass only (SG), and young pine intercropped with switchgrass (IC). The treatment watersheds were replicated on three sites located across the Southeastern U.S. in Carteret, NC; Calhoun, MS; and Greene, AL. Despite the growth inconsistency for the SG only treatment, remote modeling estimation of ET parameters yielded an acceptable R2 > 0.70, and the ET model yielded R2 of 0.50 and a standard error of prediction of 0.94. However, ET and ET parameter model estimation for the IC performed somewhat less satisfactorily, with an R2 of 0.47, 0.59, 0.56, 0.81, and 0.57 for ET, LAI, gs, Tc, and SM, respectively, potentially due to inconsistencies in Landsat image pixel size and landuse homogeneity. Moreover, ET parameter models for the YP site performed rather poorly, with R2 = 0.28, 0.63, and 0.76 for LAI, gs, and Tc, respectively. Additionally, image analysis automation was created with Python scripting and geospatial models. The findings from this study suggest that inclusion of more spatial variability, sound data mining, ultra-high resolution imagery and advanced image processing approaches to account for potential modeling uncertainties can enhance the predictive capability of models to remotely estimate environmental parameters including ET. Radial Basis Function Network (RBFN) based models provided promising results for estimating ET and ET parameters using remotely-sensed digital information when they are prepared with advanced data mining, but it is likely that laypersons may find these models difficult to use. However, forest managers with access to neural network software can use our devised RBFN training models for estimating those forest hydrologic parameters with better accuracy.}, journal={ENVIRONMENTAL MODELLING & SOFTWARE}, author={Panda, Sudhanshu Sekhar and Amatya, Devendra Man and Muwamba, Augustine and Chescheir, George}, year={2019}, month={Nov} }
 @article{cacho_youssef_shi_chescheir_skaggs_tian_leggett_sucre_nettles_arellano_2019, title={Impacts on soil nitrogen availability of converting managed pine plantation into switchgrass monoculture for bioenergy}, volume={654}, ISSN={["1879-1026"]}, DOI={10.1016/j.scitotenv.2018.11.133}, abstractNote={Biofuels derived from lignocellulosic materials is one of the options in addressing issues on climate change and energy independence. One of the most promising bioenergy crops is switchgrass (Panicum virgatum L.), particularly in North America. Future advancement in large-scale conversion of lignocellulosic feedstocks and relatively more competitive price for biomass and other economic advantages could lead to landowners opting to venture on switchgrass monoculture (SWITCH) in lieu of loblolly pine monoculture (PINE). Therefore, we investigated the conversion of previously managed loblolly pine stand into SWITCH in eastern North Carolina, U.S.A. on soil N availability. Treatments included PINE, SWTICH, and mature loblolly pine stand (REF). Each treatment was replicated three times on 0.8 ha plots drained by open ditches dug 1.0–1.2 m deep and spaced at 100 m. Rates of net N mineralization (Nm) and nitrification (Nn) at the top 20 cm were measured using sequential in-situ techniques in 2011 and 2012 (the 3rd and 4th years of establishment, respectively) along with a one-time laboratory incubation. On average, PINE, SWITCH, and REF can have field net Nm rates up to 0.40, 0.34 and 0.44 mg N·kg soil−1·d−1, respectively, and net Nn rates up to 0.14, 0.08 and 0.10 mg N·kg soil−1·d−1, respectively. Annually, net Nm rates ranged from 136.98 to 167.21, 62.00 to 142.61, and 63.57 to 127.95 kg N·ha−1, and net Nn rates were 56.31–62.98, 16.45–30.45, 31.99–32.94 kg N·ha−1 in PINE, SWITCH, and REF, respectively. Treatment effect was not significant on field Nm rate (p = 0.091). However, SWITCH significantly reduced nitrate-N production (p < 0.01). Overall, results indicated that establishment of SWITCH on poorly drained lands previously under PINE is less likely to significantly impact total soil N availability and potentially has minimum N leaching losses since soil mineral N under this system will be dominated by ammonium-N.}, journal={SCIENCE OF THE TOTAL ENVIRONMENT}, author={Cacho, Julian F. and Youssef, Mohamed A. and Shi, Wei and Chescheir, George M. and Skaggs, R. Wayne and Tian, Shiying and Leggett, Zakiya H. and Sucre, Eric B. and Nettles, Jami E. and Arellano, Consuelo}, year={2019}, month={Mar}, pages={1326–1336} }
 @article{maxwell_birgand_schipper_christianson_tian_helmers_williams_chescheir_youssef_2019, title={Increased Duration of Drying–Rewetting Cycles Increases Nitrate Removal in Woodchip Bioreactors}, volume={4}, ISSN={2471-9625}, url={http://dx.doi.org/10.2134/ael2019.07.0028}, DOI={10.2134/ael2019.07.0028}, abstractNote={Core Ideas
Nitrate removal in woodchips increased linearly with drying–rewetting duration.
Nitrate removal increased up to 172% in the longest drying–rewetting duration.
Nitrate removal rates increased proportionally with dissolved organic C leaching.
}, number={1}, journal={Agricultural & Environmental Letters}, publisher={American Society of Agronomy}, author={Maxwell, Bryan M. and Birgand, François and Schipper, Louis A. and Christianson, Laura E. and Tian, Shiying and Helmers, Matthew J. and Williams, David J. and Chescheir, George M. and Youssef, Mohamed A.}, year={2019} }
 @article{poole_skaggs_youssef_chescheir_crozier_2018, title={EFFECT OF DRAINAGE WATER MANAGEMENT ON NITRATE NITROGEN LOSS TO TILE DRAINS IN NORTH CAROLINA}, volume={61}, ISSN={["2151-0040"]}, DOI={10.13031/trans.12296}, abstractNote={Abstract.}, number={1}, journal={TRANSACTIONS OF THE ASABE}, author={Poole, C. A. and Skaggs, R. W. and Youssef, M. A. and Chescheir, G. M. and Crozier, C. R.}, year={2018}, pages={233–244} }
 @article{tian_fischer_chescheir_youssef_cacho_king_2018, title={Microtopography-induced transient waterlogging affects switchgrass (Alamo) growth in the lower coastal plain of North Carolina, USA}, volume={10}, ISSN={["1757-1707"]}, DOI={10.1111/gcbb.12510}, abstractNote={Abstract}, number={8}, journal={GLOBAL CHANGE BIOLOGY BIOENERGY}, author={Tian, Shiying and Fischer, Milan and Chescheir, George M. and Youssef, Mohamed A. and Cacho, Julian F. and King, John S.}, year={2018}, month={Aug}, pages={577–591} }
 @article{ssegane_amatya_muwamba_chescheir_appelboom_tollner_nettles_youssef_birgand_skaggs_et al._2017, title={Calibration of paired watersheds: Utility of moving sums in presence of externalities}, volume={31}, ISSN={0885-6087}, url={http://dx.doi.org/10.1002/hyp.11248}, DOI={10.1002/hyp.11248}, abstractNote={Abstract}, number={20}, journal={Hydrological Processes}, publisher={Wiley}, author={Ssegane, H. and Amatya, D. M. and Muwamba, A. and Chescheir, G. M. and Appelboom, T. and Tollner, E. W. and Nettles, J. E. and Youssef, M. A. and Birgand, François and Skaggs, R. W. and et al.}, year={2017}, month={Sep}, pages={3458–3471} }
 @article{messer_burchell_birgand_broome_chescheir_2017, title={Nitrate removal potential of restored wetlands loaded with agricultural drainage water: A mesocosm scale experimental approach}, volume={106}, ISSN={0925-8574}, url={http://dx.doi.org/10.1016/j.ecoleng.2017.06.022}, DOI={10.1016/j.ecoleng.2017.06.022}, abstractNote={Wetland restoration is often conducted in Eastern U.S. coastal plain watersheds alongside agricultural lands that frequently export significant amounts of nitrogen in drainage water. Restoration plans that incorporate the addition of agricultural drainage water can simultaneously increase the success of achieving a target hydroperiod and reduce discharge of nitrogen to nearby surface water. The potential nitrogen removal effectiveness of two wetland restoration sites with such a restoration plan was evaluated in a two-year mesocosm study. Six large wetland mesocosms (3.5 m long × 0.9 m wide × 0.75 m deep) along with unplanted controls were used in this experiment. Three replicates of two soils that differed in organic matter and pH were planted with soft-stem bulrush (Schoenoplectus tabernaemontani) and allowed to develop in the two growing seasons prior to the study. Simulated drainage water was loaded into the mesocosms over eighteen batch studies across seasons with target nitrate-N levels between 2.5 to 10 mg L−1. Grab samples were collected from the water column and analyzed for nitrate-N, dissolved organic carbon, and chloride, along with other environmental parameters such as pH, water temperature, and soil redox. Seasonally, nitrogen and carbon within the wetland plants and soil were also measured. Multivariate statistical analyses were utilized to determine differences in nitrate-N reductions between treatments. Variables included carbon availability, temperature, antecedent moisture condition, nitrogen loading, and water pH. Contrary to the hypothesis that higher nitrate-N removal rates would be observed in the wetlands with higher organic matter, overall removal rates were higher in the wetland mesocosms containing Deloss soils (WET-Min) (maximum of 726 mg m−2 d−1) than those containing Scuppernong soil (WET-Org) (maximum of 496 mg m−2 d−1) and were dependent on daily NO3-N concentrations and season. Significant differences in NO3-N removal were found between seasons and soil types (α = 0.05), which helped to provide insight to the expected magnitude of nitrogen removal within these systems throughout the year, and potential mechanisms (i.e. denitrification vs. plant uptake) that will govern these removals.}, journal={Ecological Engineering}, publisher={Elsevier BV}, author={Messer, Tiffany L. and Burchell, Michael R., II and Birgand, François and Broome, Stephen W. and Chescheir, George}, year={2017}, month={Sep}, pages={541–554} }
 @article{tian_cacho_youssef_chescheir_fischer_nettles_king_2017, title={Switchgrass growth and pine-switchgrass interactions in established intercropping systems}, volume={9}, ISSN={["1757-1707"]}, DOI={10.1111/gcbb.12381}, abstractNote={Abstract}, number={5}, journal={GLOBAL CHANGE BIOLOGY BIOENERGY}, author={Tian, Shiying and Cacho, Julian F. and Youssef, Mohamed A. and Chescheir, George M. and Fischer, Milan and Nettles, Jami E. and King, John S.}, year={2017}, month={May}, pages={845–857} }
 @article{muwamba_amatya_chescheir_nettles_appelboom_ssegane_tollner_youssef_birgand_skaggs_et al._2017, title={Water Quality Effects of Switchgrass Intercropping on Pine Forest in Coastal North Carolina}, volume={60}, ISSN={2151-0040}, url={http://dx.doi.org/10.13031/trans.12181}, DOI={10.13031/trans.12181}, abstractNote={Abstract.}, number={5}, journal={Transactions of the ASABE}, publisher={American Society of Agricultural and Biological Engineers (ASABE)}, author={Muwamba, Augustine and Amatya, Devendra M. and Chescheir, George M. and Nettles, Jami E. and Appelboom, Timothy and Ssegane, Herbert and Tollner, Ernest E and Youssef, Mohamed A. and Birgand, Francois and Skaggs, R. Wayne and et al.}, year={2017}, pages={1607–1620} }
 @article{negm_youssef_chescheir_skaggs_2016, title={DRAINMOD-based tools for quantifying reductions in annual drainage flow and nitrate losses resulting from drainage water management on croplands in eastern North Carolina}, volume={166}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2015.12.014}, abstractNote={Nitrogen (N) leachate of drained agriculture has continued to be pervasive in the U.S. water resources. Nitrogen credit exchange program is a trading market to facilitate pollutant reductions and protect the environment. A simple tool suitable for eastern North Carolina (NC) was developed to quantify drainage flow and N mass reductions resulting from drainage water management (DWM); an efficient and common conservation practice for drained agricultural lands. The tool comprises a set of regression equations estimating the performance of DWM as a function of local site conditions. DRAINMOD and DRAINMOD-NII models simulations were conducted for a wide range of soil types, weather conditions, and management practices for different locations in eastern NC. Simulation results were used with SAS 9.3 software to develop a set of multi-linear regression equations to estimate DWM-caused reductions in annual drainage flow and corresponding nitrate-N (NO3-N) losses for continuous corn (CC) and corn–wheat–soybean (CWS) cropping systems. The regression model estimations of annual drainage flow were highly correlated with DRAINMOD simulated values with an adjusted coefficient of multiple determination (R2adj) equal to 0.91 or higher for different management scenarios. Similarly, the regression model estimations of annual nitrate losses achieved an R2adj of 0.88 or higher for all management scenarios. The developed regression models were further compared on a year-by-year basis to the calibrated DRAINMOD and DRAINMOD-NII models for local conditions of an experimental site in eastern NC over 25 years. Estimated annual drainage flow and NO3-N losses were in good agreement with corresponding values simulated by DRAINMOD-based models for CC and CWS under free and controlled drainage modes. In terms of DWM-induced annual reductions in drainage flow and N losses, noticeable differences occurred in several years between predictions of DRAINMOD-NII and the regression models. A comparison based on the 5-year moving average of DWM-induced reductions smoothed out the extreme year-to-year variations and indicated very similar reduction trends provided by both methods. The results presented in this case study indicated that the simple regression method provides an adequate alternative to the processes based DRAINMOD suite of models for estimating annual reductions in drainage rates and N mass losses resulting from implementation of DWM. Similar tools can be developed for other regions in the US and abroad that initiate nitrogen trading markets involving DWM.}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Negm, L. M. and Youssef, M. A. and Chescheir, G. M. and Skaggs, R. W.}, year={2016}, month={Mar}, pages={86–100} }
 @article{skaggs_tian_chescheir_amatya_youssef_2016, title={Forest drainage}, DOI={10.1079/9781780646602.0124}, abstractNote={This chapter reviews the impacts of drainage on forest production and the hydrology of forested lands. It is established that drainage is used to improve access and yields on a small percentage of the world's forested lands. However, it has had a big impact on the millions of hectares on which it is applied. Drainage has increased timber yields on poorly drained peatlands and mineral soils in northern Europe, Canada and the southern USA.}, journal={Forest Hydrology: Processes, Management and Assessment}, author={Skaggs, R. W. and Tian, S. and Chescheir, G. M. and Amatya, D. M. and Youssef, M. A.}, year={2016}, pages={124–140} }
 @article{muwamba_amatya_ssegane_chescheir_appelboom_tollner_nettles_youssef_birgand_skaggs_et al._2015, title={Effects of Site Preparation for Pine Forest/Switchgrass Intercropping on Water Quality}, volume={44}, ISSN={0047-2425}, url={http://dx.doi.org/10.2134/jeq2014.11.0505}, DOI={10.2134/jeq2014.11.0505}, abstractNote={A study was initiated to investigate the sustainability effects of intercropping switchgrass ( L.) in a loblolly pine ( L.) plantation. This forest-based biofuel system could possibly provide biomass from the perennial energy grass while maintaining the economics and environmental benefits of a forest managed for sawtimber. Operations necessary for successful switchgrass establishment and growth, such as site preparation, planting, fertilizing, mowing and baling, may affect hydrology and nutrient runoff. The objectives of this study were (i) to characterize the temporal effects of management on nutrient concentrations and loadings and (ii) to use pretreatment data to predict those treatment effects. The study watersheds (∼25 ha each) in the North Carolina Atlantic Coastal Plain were a pine/switchgrass intercropped site (D1), a midrotation thinned pine site with natural understory (D2), and a switchgrass-only site (D3). Rainfall, drainage, water table elevation, nitrogen (total Kjedahl N, NH-N, and NO-N), and phosphate were monitored for the 2007-2008 pretreatment and the 2009-2012 treatment periods. From 2010 to 2011 in site D1, the average NO-N concentration effects decreased from 0.18 to -0.09 mg L, and loads effects decreased from 0.86 to 0.49 kg ha. During the same period in site D3, the average NO-N concentration effects increased from 0.03 to 0.09 mg L, and loads effects increased from -0.26 to 1.24 kg ha. This study shows the importance of considering water quality effects associated with intensive management operations required for switchgrass establishment or other novel forest-based biofuel systems.}, number={4}, journal={Journal of Environment Quality}, publisher={American Society of Agronomy}, author={Muwamba, A. and Amatya, D. M. and Ssegane, H. and Chescheir, G.M. and Appelboom, T. and Tollner, E.W. and Nettles, J. E. and Youssef, M. A. and Birgand, F. and Skaggs, R. W. and et al.}, year={2015}, pages={1263} }
 @article{cacho_youssef_chescheir_skaggs_leggett_sucre_nettles_arellano_2015, title={Impacts of switchgrass-loblolly pine intercropping on soil physical properties of a drained forest}, volume={58}, DOI={10.13031/trans.58.11238}, abstractNote={Intercropping switchgrass ( L.) with managed loblolly pine ( L.) has been proposed as an alternative source of bioenergy feedstock that does not require conversion of agricultural cropland. Different management practices may alter soil physical properties (SPP), which could influence productivity, hydrologic and biogeochemical processes. Therefore, we investigated the effect of switchgrass-loblolly pine intercropping on the SPP of a poorly drained forest soil in eastern North Carolina using three management regimes: young loblolly pine stand (PINE), switchgrass-pine intercropping (PSWITCH), and a 38-year-old loblolly pine stand (REF). Measurements of SPP were conducted before and after the third annual harvesting operation using intact soil cores taken from three points within each of three replicated plots and at three depths: 0-15 cm, 15-30 cm, and 30-45 cm. Pre- and post-harvest values of SPP in PSWITCH were not significantly different. Compared to PINE, changes in bulk density and in both total porosity and saturated hydraulic conductivity in PSWITCH were significant only in the top 30 and 15 cm of soil, respectively. Volume drained and drainable porosity in PSWITCH decreased significantly at water table depths ≤45 cm. Cumulative effects of V-shearing for switchgrass seedbed preparation and the first and second harvest operations may have caused structural changes to the surface soil layer in PSWITCH that subsequently resulted in the measured differences in SPP between PSWITCH and PINE. We suggest that soil disturbance should be minimized during field operations to lessen the adverse effects on SPP, and models used to quantify impacts of management practices and land use change on the hydrology and biogeochemistry of managed forests should consider SPP changes caused by management regimes.}, number={6}, journal={Transactions of the ASABE}, author={Cacho, J. F. and Youssef, M. A. and Chescheir, G. M. and Skaggs, R. W. and Leggett, Zakiya H and Sucre, E. B. and Nettles, J. E. and Arellano, C.}, year={2015}, pages={1573–1583} }
 @article{tian_cacho_youssef_chescheir_nettles_2015, title={Switchgrass growth and morphological changes under established pine-grass agroforestry systems in the lower coastal plain of North Carolina, United States}, volume={83}, ISSN={["1873-2909"]}, DOI={10.1016/j.biombioe.2015.10.002}, abstractNote={Switchgrass (Panicum virgatum L.) intercropped with Loblolly pine (Pinus taeda L.) has been proposed as a potential biomass feedstock for biofuel production in the southeastern United States. This study investigated effects of treatments (intercropping vs. grass only) on biomass increment processes and morphological properties of switchgrass at two experimental plots (Lenoir1) located in the coastal plain of North Carolina. We also evaluated effects of trimming lower tree branches of pine trees on switchgrass growth at another watershed-scale site (Carteret7) in the same region. Results showed that biomass yield of intercropped switchgrass was reduced by adjacent trees and negatively affected by relative position of grass to trees at the 6th year after planting at Lenoir1. Relative grass-to-tree position was also found to be a significant (p < 0.001) factor affecting grass growth at Carteret7 site with tree age of 5 years old, which is irrespective to the trimming practice. Trimming lower tree branches did not significantly (p = 0.57) improve biomass yield of switchgrass at Carteret7. We also observed intercropped switchgrass typically had higher specific leaf area and grew taller compared to grass-only plots. Stem-to-leaf ratios of switchgrass were significantly (p = 0.02) affected by trees at Lenoir1, but not by trimming lower branches in Carteret7 and relative position of grass to trees at both study sites. Findings from this study are important for evaluating the viability of producing biofuel feedstocks using this proposed intercropping system in the southeastern United States.}, journal={BIOMASS & BIOENERGY}, author={Tian, Shiying and Cacho, Julian F. and Youssef, Mohamed A. and Chescheir, George M. and Nettles, Jami E.}, year={2015}, month={Dec}, pages={233–244} }
 @article{tian_youssef_sun_chescheir_noormets_amatya_skaggs_king_mcnulty_gavazzi_et al._2015, title={Testing DRAINMOD-FOREST for predicting evapotranspiration in a mid-rotation pine plantation}, volume={355}, ISSN={["1872-7042"]}, DOI={10.1016/j.foreco.2015.03.028}, abstractNote={Evapotranspiration (ET) is a key component of the hydrologic cycle in terrestrial ecosystems and accurate description of ET processes is essential for developing reliable ecohydrological models. This study investigated the accuracy of ET prediction by the DRAINMOD-FOREST after its calibration/validation for predicting commonly measured hydrological variables. The model was tested by conducting an eight year simulation of drainage and shallow groundwater dynamics in a managed mid-rotation loblolly pine (Pinus taeda L.) plantation located in the coastal plain of North Carolina, USA. Modeled daily ET rates were compared to those measured in the field using the eddy covariance technique. In addition, the wavelet transform and coherence analysis were used to compare ET predictions and measurements on the time–frequency domain. Results showed that DRAINMOD-FOREST accurately predicted annual and monthly ET after a successful calibration and validation using measured drainage rates and water table depth. The model under predicted ET on an annual basis by 2%, while the Nash–Sutcliffe coefficient of model predictions on a monthly basis was 0.78. Results from wavelet transform and coherence analysis demonstrated that the model reasonably captured the high power spectra of ET at an annual scale with significantly high model-data coherency. These results suggested that the calibrated DRAINMOD-FOREST collectively captured key factors and mechanisms controlling ET dynamics in the drained pine plantation. However, the global power spectrum revealed that the model over predicted the power spectrum of ET at an annual scale, suggesting the model may have under predicted canopy conductance during non-growing seasons. In addition, this study also suggested that DRAINMOD-FOREST did not properly capture the seasonal dynamics of ET under extreme drought conditions with deeper water table depths. These results suggested further refinement to parameters, particularly vegetation related, and structures of DRAINMOD-FOREST to achieve better agreement between ET predictions and measurements in the time–frequency domain.}, journal={FOREST ECOLOGY AND MANAGEMENT}, author={Tian, Shiying and Youssef, Mohamed A. and Sun, Ge and Chescheir, George M. and Noormets, Asko and Amatya, Devendra M. and Skaggs, R. Wayne and King, John S. and McNulty, Steve and Gavazzi, Michael and et al.}, year={2015}, month={Nov}, pages={37–47} }
 @article{petru_chescheir_ahn_2014, title={Assessment of water budgets and the hydrologic performance of a created mitigation wetland-A modeling approach}, volume={71}, ISSN={["1872-6992"]}, DOI={10.1016/j.ecoleng.2014.08.001}, abstractNote={The study used a water balance model (DRAINMOD) to compute water budgets of a mitigation wetland created in the Piedmont region of Virginia. The calibration of the model was conducted with automated well data collected during the 17 month monitoring period along with precipitation, temperature, soil physical properties (soil water characteristic curve and saturated hydraulic conductivity) and estimated site characteristics (surface roughness and surface storage). The model was tested for two areas, one nondisturbed and the other disturbed, by construction practices commonly adopted for a mitigation wetland created in the region. A third model was created to represent the disturbed boundary conditions (wetland design), but substituted soil data observed at the nondisturbed study area. DRAINMOD successfully predicted the hydrologic regimes of both nondisturbed and disturbed areas. The model of the nondisturbed area could not accurately predict hydrology of the disturbed area. More importantly, the model of the disturbed area with the soils data from the nondisturbed area could not accurately predict the hydrology of the disturbed area. The models were used to evaluate a set of performance criteria across a 60-year (1952 to 2011) simulation period. Ponding for longer than 60 consecutive days during the growing season occurred at the disturbed study area in 39 out of 60 years and these conditions lasted the entire growing season (219 days) in multiple years. Prolonged inundation of the surface for longer than 100 consecutive days took place in at least 15 of the years simulated compared to two years in the nondisturbed model. The modified disturbed model (using nondisturbed soil data) satisfied jurisdictional hydrology more frequently compared to the disturbed model (33 years versus 22 years, respectively) and prolonged inundation was limited to 8 years during the simulation period with the longest single event lasting 168 consecutive days. The differences were attributed to the reduced drainable porosity and vertical saturated hydraulic conductivity in the disturbed wetland area which translated to a demand for surface storage in order to achieve accurate model calibration and jurisdictional wetland hydrology. The study shows that disturbance to key soil properties will require surface storage to achieve jurisdictional hydrology, and that construction practices can result in longer durations of ponding during the growing season, thus potentially altering the habitat type for the wetland from what was originally designed (e.g., from a forested wetland to open water or emergent habitats).}, journal={ECOLOGICAL ENGINEERING}, author={Petru, Bradley J. and Chescheir, George M. and Ahn, Changwoo}, year={2014}, month={Oct}, pages={667–676} }
 @article{negm_youssef_skaggs_chescheir_kladivko_2014, title={DRAINMOD-DSSAT Simulation of the Hydrology, Nitrogen Dynamics, and Plant Growth of a Drained Corn Field in Indiana}, volume={140}, ISSN={["1943-4774"]}, DOI={10.1061/(asce)ir.1943-4774.0000738}, abstractNote={AbstractDRAINMOD-DSSAT is an integrated model recently developed to simulate the hydrology, water quality, and crop growth for artificially drained croplands. DRAINMOD-DSSAT is an advanced research tool that contributes to increasing productivity, reducing cost, and enhancing sustainability of crop production on high water table soils with artificial drainage. In this study, the performance of the model was evaluated using a six-year data set (1985–1990) collected from a subsurface drained agricultural research site in Indiana in the United States. Subsurface drains were installed at three different spacings (5, 10, and 20 m). During the simulation period, all treatments were planted to corn receiving high preplant N-fertilization rates. Rainfall patterns varied significantly among the years. DRAINMOD-DSSAT predictions of monthly and annual drainage flow, and nitrate losses, were in good agreement with measured values. Similarly, variations in corn yield patterns were well captured by the model across dif...}, number={8}, journal={JOURNAL OF IRRIGATION AND DRAINAGE ENGINEERING}, author={Negm, Lamyaa M. and Youssef, Mohamed A. and Skaggs, Richard W. and Chescheir, George M. and Kladivko, Eileen J.}, year={2014}, month={Aug} }
 @article{petru_ahn_chescheir_2013, title={Alteration of soil hydraulic properties during the construction of mitigation wetlands in the Virginia Piedmont}, volume={51}, ISSN={["1872-6992"]}, DOI={10.1016/j.ecoleng.2012.12.073}, abstractNote={Wetland hydrology is a critical component to the success of mitigation projects. The alteration of soil hydraulic properties during the construction may influence the hydrology of the wetland, thus affecting the mitigation success. We studied disturbed (i.e. by construction) and nondisturbed areas of two wetland mitigation banks (Blackjack, BJ and Peters Farm, PF), both located in the piedmont region of Virginia, for a variety of soil hydraulic and physicochemical properties. The surface soil horizon at BJ showed an increase in clay content from 18.6 to 40%, decrease in bulk density (Db) from 1.56 to 1.45 g/cm3, decrease the drained volume (Dv) of water in the soil profile from 0.67 to 0.36 cm, decrease in available water content (AWC) from 22.7 to 15.8%, and a reduction in the ratio of AWC to TPS from 66 to 40%. Soil at PF showed an increase in clay content in the surface horizon from 20 to 30%, increase TPS from 37.2 to 40.0%, increase Db from 1.52 to 1.67 g/cm3, increase the Dv in the soil profile from 3.5 to 6.6 cm, increase in AWC from 37.2 to 40.2%, and a decrease in the ratio of AWC to TPS from 58 to 44% in the surface horizon. The outcome showed that the impacts of common construction practices for mitigation wetlands affected drainable and plant available subsurface water storage, more so in fine grained soils. Key soil hydraulic properties should be considered in the disturbed or ameliorated state before water budgets are constructed to model wetland hydrology. Further studies are needed to investigate how the plant available and drainable water contents can be affected by construction practices in various soil textures, and how these properties might change in the long term.}, journal={ECOLOGICAL ENGINEERING}, author={Petru, Bradley J. and Ahn, Changwoo and Chescheir, George}, year={2013}, month={Feb}, pages={140–150} }
 @article{poole_skaggs_cheschier_youssef_crozier_2013, title={Effects of drainage water management on crop yields in North Carolina}, volume={68}, ISSN={["1941-3300"]}, DOI={10.2489/jswc.68.6.429}, abstractNote={Research studies on a wide range of soils, crops, locations, and climates have shown that drainage water management (DWM), or controlled drainage (CD), can be used to substantially reduce the loss of nitrogen (N), and in some cases, phosphorus (P) from drained agricultural lands to surface waters. The adoption and widespread application of DWM depends on a variety of factors including its impact on crop yields. This paper presents results from a long term field study on the effect of DWM or CD on crop yields in a three-crop, two-year corn/wheat–soybean rotation. Yields were measured on replicated field scale plots under CD and conventional or free drainage (FD) treatments for a total of 18 crops on two experimental sites during the period from 1990 to 2011. Data were collected on 7 corn (Zea mays L.) crops, 5 wheat (Triticum aestivum L.) crops, and 6 soybean (Glycine max L.) crops. Controlled drainage had no significant effect on yields of winter wheat, which in North Carolina is grown in the wettest, coolest part of the year. Controlled drainage increased corn yields compared to FD in all seven years. The average yield increase for corn was 11%. Controlled drainage also increased soybean yield in all years with an average increase of 10% compared to FD. Such yield responses will promote the application of DWM, which will result in both economic and environmental benefits.}, number={6}, journal={JOURNAL OF SOIL AND WATER CONSERVATION}, author={Poole, C. A. and Skaggs, R. W. and Cheschier, G. M. and Youssef, M. A. and Crozier, C. R.}, year={2013}, pages={429–437} }
 @article{kim_amatya_chescheir_skaggs_nettles_2013, title={Hydrologic Effects of Size and Location of Fields Converted from Drained Pine Forest to Agricultural Cropland}, volume={18}, ISSN={["1943-5584"]}, DOI={10.1061/(asce)he.1943-5584.0000566}, abstractNote={AbstractHydrological effects of land-use change are of great concern to ecohydrologists and watershed managers, especially in the Atlantic coastal plain of the southeastern United States. The concern is attributable to rapid population growth and the resulting pressure to develop forested lands. Many researchers have studied these effects in various scales, with varying results. An extended watershed-scale forest hydrologic model, calibrated with 1996–2000 data, was used to evaluate long-term hydrologic effects of conversion to agriculture (corn–wheat–soybean cropland) of a 29.5-km2 intensively managed pine-forested watershed in Washington County in eastern North Carolina. Fifty years of weather data (1951–2000) from a nearby weather station were used for simulating hydrology to evaluate effects on outflows, evapotranspiration, and water table depth compared with the baseline scenario. Other simulation scenarios were created for each of five different percentages (10, 25, 50, 75, and 100%) of land-use con...}, number={5}, journal={JOURNAL OF HYDROLOGIC ENGINEERING}, author={Kim, Hyun Woo and Amatya, Devendra M. and Chescheir, George M. and Skaggs, Wayne R. and Nettles, Jami E.}, year={2013}, month={May}, pages={552–566} }
 @article{price_burchell_hunt_chescheir_2013, title={Long-term study of dune infiltration systems to treat coastal stormwater runoff for fecal bacteria}, volume={52}, ISSN={0925-8574}, url={http://dx.doi.org/10.1016/j.ecoleng.2012.12.008}, DOI={10.1016/j.ecoleng.2012.12.008}, abstractNote={Abstract The discharge of untreated stormwater runoff into recreational waters places swimmers at risk of contracting various illnesses and often results in beach closures or swimming advisories. In an effort to safeguard the public, two experimental Dune Infiltration Systems were installed beneath the sand dunes in Kure Beach, NC. The systems diverted stormwater from two existing beach outfalls, which drained 1.9 ha (4.7 ac) and 3.2 ha (8.0 ac) watersheds, into subsurface chambers for temporary storage and infiltration into the existing sand dunes. A 3-year study examined the long-term performance of the two systems during which 14,584 m 3 (515,046 ft 3 ) of stormwater was diverted into the dunes, with only 438 m 3 (15,457 ft 3 ) bypassing the systems, a nearly 97% capture rating. Enterococci concentrations in stormwater runoff from the watersheds exceeded the state's single sample maximum for Tier I waters (104 MPN/100 mL) in >70% of samples, with geometric means ≥278 MPN/100 mL. Groundwater enterococci concentrations tended to remain below the state limit (≤11% exceedance), with geometric means ≤7 MPN/100 mL. Groundwater monitoring in the control dune, with no direct input of stormwater, had a geometric mean of 5 MPN/100 mL and a 6% exceedance rate. The influences on the local water tables were temporary, as the water table would mound around the systems during infiltration events and dissipate to within pre-storm variations from the control within hours or up to approximately 2 weeks. The Dune Infiltration System appears appropriate for installation in small watersheds (}, journal={Ecological Engineering}, publisher={Elsevier BV}, author={Price, W.D. and Burchell, M.R., II and Hunt, W.F. and Chescheir, G.M.}, year={2013}, month={Mar}, pages={1–11} }
 @misc{tian_youssef_skaggs_chescheir_amatya_2013, title={Predicting dissolved organic nitrogen export from a drained loblolly pine plantation}, volume={49}, ISSN={["1944-7973"]}, DOI={10.1002/wrcr.20157}, abstractNote={Key Points}, number={4}, journal={WATER RESOURCES RESEARCH}, author={Tian, Shiying and Youssef, Mohamed A. and Skaggs, R. Wayne and Chescheir, G. M. and Amatya, Devendra M.}, year={2013}, month={Apr}, pages={1952–1967} }
 @misc{amatya_rossi_saleh_dai_youssef_williams_bosch_chescheir_sun_skaggs_et al._2013, title={Review of nitrogen fate models applicable to forest landscapes in the southern US}, volume={56}, DOI={10.13031/trans.56.10096}, abstractNote={Assessing the environmental impacts of fertilizer nitrogen (N) used to increase productivity in managed forests is complex due to a wide range of abiotic and biotic factors affecting its forms and movement. Models developed to predict fertilizer N fate (e.g., cycling processes) and water quality impacts vary widely in their design, scope, and potential appli- cation. We review the applicability of five commonly used eco-hydrologic models (APEX, MIKESHE-DNDC, DRAIN- MOD-FOREST, REMM, and SWAT) in assessing N fate and transport in southern forest landscapes ( 50 km 2 ), although N routing below the subbasin level does not yet exist. Similarly, the dis- tributed MIKESHE-DNDC model has been used to assess N cycles across different spatial scales, on both uplands and lowlands, but was not intended to model lateral N transport. However, MIKESHE alone is capable of describing the hy- drology and N transport. The strengths of each of the models reflect their original design and scope intent. Based on this review, none of the five models that we considered is independently adequate to address the fate of N fertilizers applied to forest stands at both small and large scales, including uplands and lowlands. While efforts are underway to extend these tools' capabilities and address their various limitations, the models must be validated using experimental data before us- ing their outputs, together with uncertainty analysis, for developing forest fertilization guidelines and the fate and transport of N.}, number={5}, journal={Transactions of the ASABE}, author={Amatya, D. M. and Rossi, C. G. and Saleh, A. and Dai, Z. and Youssef, M. A. and Williams, R. G. and Bosch, D. D. and Chescheir, G. M. and Sun, G. and Skaggs, R. W. and et al.}, year={2013}, pages={1731–1757} }
 @article{skaggs_youssef_chescheir_2012, title={A Drainmod-based method to estimate effects of drainage water management on annual nitrogen loss to surface water}, volume={55}, DOI={10.13031/2013.41515}, abstractNote={Effects of drainage water management (DWM) on nitrogen (N) losses to surface waters can be estimated by multiplying the change in subsurface drainage and surface runoff, as predicted by DRAINMOD, by long-term mean nitrogen (N) concentration, which is a function of local site conditions (climate, soil, cropping system, farming practices, and drainage system). Consistent with experimental observations from several sources, this approximate method assumes that the effect of DWM on N losses is proportional to its effect on drainage and surface runoff volumes. The reliability of the method was evaluated by comparing estimated annual N losses for two sites (one in North Carolina and one in Illinois) to those predicted by the process-based nitrogen model DRAINMOD-NII. The long-term N concentrations used in the approximate method were based on DRAINMOD-NII predictions. DRAINMOD-NII simulations predicted that DWM would reduce long-term average N losses to surface waters by 35% for continuous corn (CC) and 33% for a corn-wheat-soybean (CWS) rotation in North Carolina and by 31% and 26% for CC and a corn-soybean (CS) rotation in Illinois. The approximate method estimated the annual effect of DWM on N losses within 3 kg ha-1 of that predicted by DRAINMOD-NII in over 68% of the years for the CWS and CS rotations at both sites and in over 51% of the years for CC. Overestimated effects in some years were balanced by underestimated effects in others. However, relatively large errors occurred in about 25% of the years when N concentrations in the drainage water varied significantly from the long-term average. These errors typically occurred following periods when crop yields deviated significantly from the average. When these outliers were excluded from the analyses, the goodness of fit between annual N losses predicted by DRAINMOD-NII and annual losses estimated by the approximate method was substantially improved (Nash-Sutcliffe EF values ranging from 0.54 to 0.79). Although more research is needed to improve the approximate method when concentrations vary significantly from the long-term average, the results presented herein indicate that the method provides a reliable means of assessing impacts of DWM under normal conditions.}, number={3}, journal={Transactions of the ASABE}, author={Skaggs, R. W. and Youssef, M. A. and Chescheir, G. M.}, year={2012}, pages={799–808} }
 @article{skaggs_youssef_chescheir_2012, title={Drainmod: model use, calibration, and validation}, volume={55}, DOI={10.13031/2013.42259}, abstractNote={DRAINMOD is a process-based, distributed, field-scale model developed to describe the hydrology of poorly drained and artificially drained soils. The model is based on water balances in the soil profile, on the field surface, and, in some cases, in the drainage system. This article briefly describes the model and the algorithms that are used to quantify the various hydrologic components. Inputs for soil properties, site parameters, weather data, and crop characteristics required in the application of the model are presented and discussed with respect to their role in calibration. Methods for determining field effective values of key inputs to the model, either independently or as a part of the calibration process, are demonstrated in a case study. The case study involved calibrating DRAINMOD with two years of field data for a subsurface drained agricultural field in eastern North Carolina, followed by testing or validation of the model with two additional years of data. Performance statistics indicated that the model with calibrated input data accurately predicted daily water table depths with Nash-Sutcliffe modeling efficiency (EF) values of 0.68 and 0.72, daily drainage rates (EF = 0.73 and 0.49), and monthly drainage volumes (EF = 0.87 and 0.77) for the two-year validation period.}, number={4}, journal={Transactions of the ASABE}, author={Skaggs, R. W. and Youssef, M. A. and Chescheir, G. M.}, year={2012}, pages={1509–1522} }
 @article{tian_youssef_skaggs_amatya_chescheir_2012, title={Modeling water, carbon, and nitrogen dynamics for two drained pine plantations under intensive management practices}, volume={264}, ISSN={["1872-7042"]}, DOI={10.1016/j.foreco.2011.09.041}, abstractNote={This paper reports results of a study to test the reliability of the DRAINMOD-FOREST model for predicting water, soil carbon (C) and nitrogen (N) dynamics in intensively managed forests. The study site, two adjacent loblolly pine (Pinus taeda L.) plantations (referred as D2 and D3), are located in the coastal plain of North Carolina, USA. Controlled drainage (with weir and orifice) and various silvicultural practices, including nitrogen (N) fertilizer application, thinning, harvesting, bedding, and replanting, were conducted on the study site. Continuous collection of hydrological and water quality data (1988–2008) were used for model evaluation. Comparison between predicted and measured hydrologic variables showed that the model accurately predicted long-term subsurface drainage dynamics and water table fluctuations in both loblolly pine plantations. Predicted mean and standard deviation of annual drainage matched measured values very well: 431 ± 217 vs. 436 ± 231 mm for D2 site and 384 ± 152 vs. 386 ± 160 mm for D3 site. Nash–Sutcliffe coefficients (NSE) were above 0.9 for drainage predictions on annual and monthly basis and above 0.86 for predictions of daily water table fluctuations. Compared to measurements in other similar studies, the model also reasonably estimated long-term dynamics of organic matter pools on forest floor and in forest soil. Predicted mean and standard deviation of annual nitrate exports were comparable to measured values: 1.6 ± 1.3 vs. 1.5 ± 1.5 kg ha−1 for D2 site, and 1.4 ± 1.3 vs. 1.3 ± 1.1 kg ha−1 for D3 site, respectively. Predicted nitrate export dynamics were also in excellent agreement with field measurements as indicated by NSE above 0.90 and 0.84 on annual and monthly bases, respectively. The model, thus successfully tested, was applied to predicted hydrological and biogeochemical responses to drainage water management and silvicultural practices. Specifically, the model predicted reduced rainfall interception and ET after clear cutting, both of which led to increased water yield and elevated water table, as expected. The model also captured temporary changes in nitrogen transformations following forest harvesting, including increased mineralization, nitrification, denitrification, and decreased plant uptake. Overall, this study demonstrated that DRAINMOD-FOREST can predict water, C and N dynamics in drained pine forests under intensive management practices.}, journal={FOREST ECOLOGY AND MANAGEMENT}, author={Tian, Shiying and Youssef, Mohamed A. and Skaggs, R. Wayne and Amatya, Devendra M. and Chescheir, George M.}, year={2012}, month={Jan}, pages={20–36} }
 @article{tian_youssef_skaggs_amatya_chescheir_2012, title={Temporal Variations and Controlling Factors of Nitrogen Export from an Artificially Drained Coastal Forest}, volume={46}, ISSN={["1520-5851"]}, DOI={10.1021/es3011783}, abstractNote={Nitrogen losses in drainage water from coastal forest plantations can constrain the long term sustainability of the system and could negatively affect adjacent nutrient sensitive coastal waters. Based on long-term (21 years) field measurements of hydrology and water quality, we investigated the temporal variations and controlling factors of nitrate and dissolved organic nitrogen (DON) export from an artificially drained coastal forest over various time scales (interannual, seasonal, and storm events). According to results of stepwise multiple linear regression analyses, the observed large interannual variations of nitrate flux and concentration from the drained forest were significantly (p < 0.004) controlled by annual mean water table depth, and annual drainage or precipitation. Annual precipitation and drainage were found to be dominant factors controlling variations of annual DON fluxes. Temporal trends of annual mean DON concentration could not be explained explicitly by climate or hydrologic factors. No significant difference was observed between nitrogen (both nitrate and DON) export during growing and nongrowing seasons. Nitrate exhibited distinguished export patterns during six selected storm events. Peak nitrate concentrations during storm events were significantly (p < 0.003) related to 30-day antecedent precipitation index and the minimum water table depth during individual events. The temporal variations of DON export within storm events did not follow a clear trend and its peak concentration during the storm events was found to be significantly (p < 0.006) controlled by the short-term drying and rewetting cycles.}, number={18}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Tian, Shiying and Youssef, Mohamed A. and Skaggs, R. Wayne and Amatya, Devendra M. and Chescheir, George M.}, year={2012}, month={Sep}, pages={9956–9963} }
 @article{skaggs_phillips_chescheir_trettin_2011, title={Effect of minor drainage on hydrology of forested wetlands}, volume={54}, DOI={10.13031/2013.40665}, abstractNote={Results of a simulation study to determine the impacts of minor drainage for silviculture on wetland hydrology are presented in this article. Long-term DRAINMOD simulations were conducted to determine the threshold drainage intensity (ditch depth and spacing) that removes wetland hydrology from forested wetlands. Analyses were conducted for 13 soil series and profile combinations at ten locations from Norfolk, Virginia, to Baton Rouge, Louisiana, in the Atlantic and Gulf coastal states. Threshold ditch spacings (LT) were obtained for five ditch depths for all combinations of soil profiles and locations. Analysis of the results showed that LT can be approximated as LT = , where T is the horizontal hydraulic transmissivity of the soil profile, and C is a coefficient dependent on ditch depth and geographic location. The C values for all combinations of ditch depth and location are given in this article. The threshold spacings can be used as benchmarks to directly evaluate the impact of drainage alternatives on wetland hydrology. They were also used herein to determine T25 inputs for previously developed methods to predict the lateral impact of a single ditch on wetland hydrology. Lateral impacts were determined and presented for a 0.9 m (3 ft) deep drainage ditch for all soils and locations considered. The T25 values presented can be used to determine lateral impacts for other ditch depths and soils. The analyses in this study were conducted for a surface depressional storage of 5 cm. More work is needed to define T25 values for smaller surface storages, including those smaller values needed for application to agricultural cropland.}, number={6}, journal={Transactions of the ASABE}, author={Skaggs, R. W. and Phillips, B. D. and Chescheir, G. M. and Trettin, C. C.}, year={2011}, pages={2139–2149} }
 @article{skaggs_chescheir_fernandez_amatya_diggs_2011, title={Effects of land use on soil properties and hydrology of drained coastal plain watersheds}, volume={54}, DOI={10.13031/2013.39037}, abstractNote={Some of the world's most productive cropland requires artificial or improved drainage for efficient agricultural production. Soil hydraulic properties, such as hydraulic conductivity and drainable porosity, are conventionally used in design of drainage systems. While it is recognized that these soil properties vary over a relatively wide range within a given soil series, it is generally assumed they can be approximated based on soil type, independent of crop or land use. Effects of land use on hydrology of drained soils in the North Carolina lower coastal plain were investigated by comparing hydrologic measurements on drained agricultural cropland, drained forest land (Loblolly pine), and an undrained forested wetland. Higher ET on the drained pine forest site resulted in reduced drainage outflow and deeper water tables compared to the agricultural site. Measurements for the wetland site showed water tables near the surface but annual outflows similar to the drained forest site. Field effective hydraulic conductivity in the top 70 cm of the drained forest site was more than two orders of magnitude greater than that of corresponding layers of the soil on the agricultural site. Drainable porosity, based on measured soil water characteristics, was also much higher for the forested sites. Long term (50-year) DRAINMOD simulations predicted average annual drainage outflow of 51.4 cm for the agricultural field as compared to 37.6 cm for the forested site. The difference resulted primarily from greater ET predicted for the forested site. Because of the high hydraulic conductivity of the surface layers and large surface depressional storage, predicted surface runoff from the forested site was nil, compared to an average annual runoff of 13 cm for the drained cropland site. Results of long-term simulations were used to analyze these effects for the widely variable seasonal and annual weather conditions of eastern North Carolina.}, number={4}, journal={Transactions of the ASABE}, author={Skaggs, R. W. and Chescheir, G. M. and Fernandez, G. P. and Amatya, D. M. and Diggs, J.}, year={2011}, pages={1357–1365} }
 @article{birgand_appelboom_chescheir_skaggs_2011, title={Estimating Nitrogen, Phosphorus, and Carbon Fluxes in Forested and Mixed-Use Watersheds of the Lower Coastal Plain of North Carolina: Uncertainties Associated with Infrequent Sampling}, volume={54}, ISSN={2151-0040}, url={http://dx.doi.org/10.13031/2013.40668}, DOI={10.13031/2013.40668}, abstractNote={Assessing the impact of a land use change or the water quality improvement provided by a treatment system almost always involves computation of the difference in nutrient loads before and after implementation, or upstream and downstream of the system studied. Reporting meaningful values on mass balance or differences in nutrient loads implies that the uncertainty in the computed loads is several times smaller than the difference itself. This may imply very small uncertainties for the nutrient load measurements. The level of uncertainty induced by infrequent sampling on annual loads was investigated for a suite of nutrients in runoff from a forested watershed and a mixed land use watershed in the lower coastal plain of North Carolina. Reference data were used to simulate discrete sampling and to calculate new annual load estimators, which were then compared to the reference loads to calculate the level of uncertainty. Uncertainties depended on the watershed and the nutrients and other constituents, but their level was generally found to be high, around ±20% and ±40% or more for weekly and monthly sampling for most nutrients. This was generally attributed to the short periods of active flow in these watersheds and the flashiness of flow associated with subsurface drainage. The results suggest that to obtain uncertainties of ±2% or ±5% for nitrogen forms, 100 or more than 200 samples over six months of the year might be necessary in the forested and mixed-use watersheds of the lower coastal plain.}, number={6}, journal={Transactions of the ASABE}, publisher={American Society of Agricultural and Biological Engineers (ASABE)}, author={Birgand, F. and Appelboom, T. W. and Chescheir, G. M. and Skaggs, R. W.}, year={2011}, pages={2099–2110} }
 @article{phillips_skaggs_chescheir_2010, title={A method to determine lateral effect of a drainage ditch on wetland hydrology: Field testing}, volume={53}, DOI={10.13031/2013.32599}, abstractNote={An approximate method was previously developed to predict the lateral effect of a drainage ditch on wetland hydrology. The method predicts the lateral distance of influence of a single ditch constructed through, or adjacent to, a wetland in terms of T25 values, which are dependent on climatological conditions. The lateral effect, or distance of influence, is defined as the width of a strip adjacent to the ditch that is drained such that it no longer satisfies wetland hydrologic criteria. T25 represents the time required for the water table to be drawn down by drainage from the surface to a depth of 25 cm at the location on the landscape that will just barely satisfy the wetland hydrologic criterion. Data to test the method were collected at two wetland mitigation sites in eastern North Carolina: Mildred Woods in Edgecombe County and ABC near Pinetown in Beaufort County. The approximate method predicted lateral effects of 42.6, 7.2, and 14.1 m for Mildred Woods, ABC shallow ditch, and the ABC deep ditch, respectively. Compared to direct interpolation of 3-year average field results for Mildred Woods (41 m) and the deep ditch (12 m), the method performed well. The lateral effect predicted by the method for the shallow ditch at the ABC site was at least two times that measured in the field (<3.75 m). In this case, the ditch was located in a tight clay layer, which substantially reduced the effective transmissivity of the profile and the lateral effect of the ditch on the hydrology of adjacent wetlands.}, number={4}, journal={Transactions of the ASABE}, author={Phillips, B. D. and Skaggs, R. W. and Chescheir, G. M.}, year={2010}, pages={1087–1096} }
 @article{appelboom_chescheir_birgand_skaggs_gilliam_amatya_2010, title={Temperature Coefficient for Modeling Denitrification in Surface Water Sediments Using the Mass Transfer Coefficient}, volume={53}, ISSN={2151-0040}, url={http://dx.doi.org/10.13031/2013.29578}, DOI={10.13031/2013.29578}, abstractNote={Watershed modeling has become an important tool for researchers. Modeling nitrate transport within drainage networks requires quantifying the denitrification within the sediments in canals and streams. In a previous study, several of the authors developed an equation using a term called a mass transfer coefficient to mathematically describe sediment denitrification. This equation takes into account the effect that water column nitrate concentration and flow depth have on denitrification in the sediments. Water column temperature also has a marked effect on the rate of denitrification in the sediments. In the present study, a relationship between denitrification rate and temperature was developed. This relationship was inserted into the original mathematical relationship to improve its ability to predict nitrate removal due to denitrification within drainage networks. The modified equation was tested by comparing predicted and measured nitrate concentrations over time in denitrification tanks at various temperatures. Results show that the modified equation increased the accuracy of predicting nitrate removal by denitrification in drainage canals. Overall Nash-Sutcliffe model efficiency values ranged from 0.72 to 0.76 for the original equation and from 0.90 to 0.97 for the equation developed in this study. The effective temperature range for the equation is 0°C to 40°C. The equation has also only been tested under stagnant/low-flow conditions.}, number={2}, journal={Transactions of the ASABE}, publisher={American Society of Agricultural and Biological Engineers (ASABE)}, author={Appelboom, T. W. and Chescheir, G. M. and Birgand, F. and Skaggs, R. W. and Gilliam, J. W. and Amatya, D.}, year={2010}, pages={465–474} }
 @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{fernandez_chescheir_skaggs_amatya_2007, title={Application of DRAINMOD-GIS to a lower coastal plain watershed}, volume={50}, DOI={10.13031/2013.22635}, abstractNote={This article reports a case study for applying DRAINMOD-GIS, a DRAINMOD-based lumped parameter watershed model, to Chicod Creek watershed, a 11100 ha coastal plain watershed in North Carolina that is not intensively instrumented or documented. The study utilized the current database of land use, topography, stream network, soil, and weather data available to state and federal agencies. Methods for collecting, evaluating, and formatting watershed data for model input are described. The study demonstrated that the lumped parameter model may be used to characterize the hydrology and water quality of Chicod Creek. Hydrology predictions were within 5% of the measured data. Predicted mean monthly nitrate-nitrogen (NO3-N) loads compared well with the measured data. Mean annual delivery ratios of each field ranged from 81% to 99% with a watershed mean of 90%. Application of the model to evaluate the effects of changing land use is presented.}, number={2}, journal={Transactions of the ASABE}, author={Fernandez, G. and Chescheir, G. M. and Skaggs, R. W. and Amatya, D. M.}, year={2007}, pages={439–447} }
 @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{stackelberg_chescheir_skaggs_amatya_2007, title={Simulation of the hydrologic effects of afforestation in the Tacuarembo River basin, Uruguay}, volume={50}, DOI={10.13031/2013.22636}, abstractNote={The Soil and Water Assessment Tool (SWAT) was used to simulate the hydrology of two small paired catchments in northern Uruguay. The control and treatment catchments (69 and 108 ha, respectively) were monitored for a three-year pretreatment period during which the land use was grassland with livestock grazing. Subsequently, the treatment catchment was planted (57% afforested) with loblolly pine (Pinus taeda). The objectives of the modeling study were to simulate the hydrologic response of the two catchments during the pretreatment period and predict the hydrologic effects of converting the native pasture to pine plantation. SWAT models of the two catchments were calibrated and validated using data measured during the pretreatment period. The model predicted outflows from the catchments reasonably well as compared to observed outflows during the years with above average rainfall (5% to -13% error). Model efficiency (E) for daily outflow volumes was greater than 0.71, indicating a good fit between simulated and observed results. A 33-year continuous simulation was performed on three land uses: grassland with livestock grazing, grassland without grazing, and pine treatment. The conversion of the catchments from the baseline pasture condition with grazing resulted in a predicted reduction in average annual water yield from the catchments of 15% for native grassland without grazing, and 23% for pine trees. A maximum predicted hydrologic effect was estimated by maximizing the model parameter that increases the ability of pine trees to withdraw water from the ground. For this condition, the model predicted a 30% reduction in mean annual water yield from the afforested catchment.}, number={2}, journal={Transactions of the ASABE}, author={Stackelberg, N. O. and Chescheir, G. M. and Skaggs, R. W. and Amatya, D. M.}, year={2007}, pages={455–468} }
 @article{burchell_skaggs_lee_broome_chescheir_osborne_2007, title={Substrate organic matter to improve nitrate removal in surface-flow constructed wetlands}, volume={36}, ISSN={["0047-2425"]}, DOI={10.2134/jeq2006.0022}, abstractNote={ABSTRACT}, number={1}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={Burchell, Michael R., II and Skaggs, R. Wayne and Lee, Charles R. and Broome, Steven and Chescheir, George M. and Osborne, Jason}, year={2007}, pages={194–207} }
 @article{fernandez_chescheir_skaggs_amatya_2006, title={DRAINMOD-GIS: A lumped parameter watershed scale drainage and water quality model}, volume={81}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2005.03.004}, abstractNote={A watershed scale lumped parameter hydrology and water quality model that includes an uncertainty analysis component was developed and tested on a lower coastal plain watershed in North Carolina. Uncertainty analysis was used to determine the impacts of uncertainty in field and network parameters of the model on the predicted outflows and nitrate–nitrogen loads at the outlet of the watershed. The model, which links DRAINMOD field hydrology and a spatially distributed routing model using a kernel function, accurately predicted the outlet flows and nitrate–nitrogen loads from a lower coastal plain watershed. Model predictions were within 1% of both measured outflows and nitrate–nitrogen loads. Uncertainty analysis indicated that uncertainty in stream velocities, decay coefficient and field exports significantly contributed to the uncertainty in the predicted outlet flows, loads and mean watershed delivery ratio.}, number={1-2}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Fernandez, GP and Chescheir, GM and Skaggs, RW and Amatya, DM}, year={2006}, month={Mar}, pages={77–97} }
 @article{skaggs_youssef_chescheir_2006, title={Drainage design coefficients for eastern United States}, volume={86}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2006.06.007}, abstractNote={The development of drainage simulation models has made it possible to quantitatively describe the performance of drainage systems, including the effects of design parameters on yields. While this was a primary goal of drainage researchers 40 years ago, it is no longer sufficient. Currently, the effect of drainage on nutrient loads and surface water quality is of equal or greater importance to production goals. Limited field data and modeling results indicate that nitrogen (N) loss in drainage water is proportional to subsurface drainage intensity (DI). This implies that the drainage system should be tailored to soil and site conditions, such that the DI is as small as possible. While simulation models can be used to determine drain depth and spacing required to maximize yields or profits for a specific site, the modeling expertise and/or the extensive data required are often not available. Simple approaches are still needed for estimating drain spacing and depth. The Hooghoudt equation has been used for many years for this purpose. Its application requires knowledge of the design drainage rate, which has not been defined for many locations in the US. A simulation study was conducted to determine the drain spacing corresponding to predicted maximum economic return for corn production on four soils at 10 locations in eastern United States. The drainage intensity (cm/day) corresponding to the optimum drain spacing was defined as the design drainage rate (DDR). DDR varied with growing season rainfall and ranged from an average (across the four soils) of 0.58 cm/day at Toledo, OH to 1.61 cm/day at Baton Rouge, LA. Variation of DDR among the four soils was least for the low rainfall locations and highest where growing season rainfall was high. The regression equation, DDR = 0.004P − 1.1, may be used to estimate DDR (cm/day) in terms of growing season rainfall, P (mm). These results were obtained for a drain depth of 1 m and surface depressional storage of 2 cm. Additional research is needed to test the relationships, and/or develop new equations, for additional drain depths and surface storages.}, number={1-2}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Skaggs, R. Wayne and Youssef, M. A. and Chescheir, G. M.}, year={2006}, month={Nov}, pages={40–49} }
 @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{grace_skaggs_chescheir_2006, title={Hydrologic and water quality effects of thinning loblolly pine}, volume={49}, DOI={10.13031/2013.20484}, abstractNote={Forest operations such as harvesting, thinning, and site preparation can affect the hydrologic behavior of watersheds on poorly drained soils. The influence of these operations conducted on organic soil sites can be more pronounced than on mineral soil sites due to the differences in bulk density and soil moisture relationships that exist between mineral and organic soils. This article reports the results of a study to evaluate the effect of thinning on the hydrology and water quality of an artificially drained pine plantation watershed on organic soils in eastern North Carolina. Outflow, water table depth, and water quality were monitored over a 3-year study period from paired 40 ha and 16 ha 15-year-old loblolly pine (Pinus taeda L.) plantations located in Washington County near Plymouth, North Carolina. Thinning increased daily outflow and peak flow rates based on a paired-watershed study design. Mean daily outflow doubled and peak flow rates increased 40% on the thinned watershed in relation to the control. Treatment effects were also observed on nutrient loads following the thinning operation. Phosphorous, TKN, and TSS loads increased following thinning, while nitrate-nitrogen loads decreased following thinning. These differences in hydrologic behavior are primarily attributed to the reduction in evapotranspiration that resulted from thinning.}, number={3}, journal={Transactions of the ASABE}, author={Grace, J. M. and Skaggs, R. W. and Chescheir, G. M.}, year={2006}, pages={645–654} }
 @article{fernandez_chescheir_skaggs_amatya_2005, title={Development and testing of watershed-scale models for poorly drained soils}, volume={48}, DOI={10.13031/2013.18323}, abstractNote={Two watershed-scale hydrology and water quality models were used to evaluate the cumulative impacts of land 
use and management practices on downstream hydrology and nitrogen loading of poorly drained watersheds. Field-scale 
hydrology and nutrient dynamics are predicted by DRAINMOD in both models. In the first model (DRAINMOD-DUFLOW), 
field-scale predictions are coupled to the canal/stream routing and in-stream water quality model DUFLOW, which handles 
flow routing and nutrient transport and transformation in the drainage canal/stream network. In the second model 
(DRAINMOD-W), DRAINMOD was integrated with a new one-dimensional canal and water quality model. The hydrology 
and hydraulic routing components of the models were tested using data from a 2950 ha drained managed forest watershed 
in the coastal plain of eastern North Carolina. Both models simulated the hydrology and nitrate-nitrogen (NO3-N) loading 
of the watershed acceptably. Simulated outflows and NO3-N loads at the outlet of the watershed were in good agreement with 
the temporal trend for five years of observed data. Over a five-year period, total outflow was within 1% of the measured value. 
Similarly, NO3-N load predictions were within 1% of the measured load. Predictions of the two models were not statistically 
different at the 5% level of significance.}, number={2}, journal={Transactions of the ASAE}, author={Fernandez, G. P. and Chescheir, G. M. and Skaggs, R. W. and Amatya, D. M.}, year={2005}, pages={639–652} }
 @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{shelby_chescheir_skaggs_amatya_2005, title={Hydrologic and water-quality response of forested and agricultural lands during the 1999 extreme weather conditions in eastern North Carolina}, volume={48}, DOI={10.13031/2013.20104}, abstractNote={This study evaluated hydrologic and water-quality data collected on a coastal-plain research watershed during a series of hurricanes and tropical storms that hit coastal North Carolina in 1999, including hurricanes Dennis, Floyd, and Irene. During September and October 1999, the research watershed received approximately 555 mm of rainfall associated with hurricanes. This was the wettest such period in a 49-year historical weather record (1951-1999). Prior to the hurricanes, the watershed experienced a dry late winter, spring, and summer (565 cm for Feb.-Aug.). This was the third driest such period in the 49-year record. Maximum daily flow rates measured across the research watershed were greater during hurricane Floyd than for any other time in a four-year (1996-1999) study of the watershed. Daily flows observed for an agricultural subwatershed were generally greater than for a forested subwatershed throughout the study, and during the hurricanes of 1999. Daily nutrient loads measured across the research watershed were greater during hurricane Floyd than for any other time in the study. In general, the two-month period of hurricanes produced total nitrogen and total phosphorus loads nearly equal to average loads for an entire year. Total annual nitrogen export from an agricultural subwatershed was 18 kg/ha in 1999, with 11 kg/ha (61%) lost during September and October. Total annual nitrogen export from a forested subwatershed was 15 kg/ha in 1999, with 10 kg/ha (67%) lost during September and October. The nitrogen export observed in the forested subwatershed was high compared to other forested areas, likely due to the highly permeable organic soils in the watershed. Total annual phosphorus export from an agricultural subwatershed was 0.9 kg/ha in 1999, with 0.7 kg/ha (78%) lost during the hurricanes/tropical storms. Total annual phosphorus load from a forested subwatershed was 0.1 kg/ha in 1999, with 74% of the load exported during the months of September and October. Hurricanes and floods occur with some regularity in North Carolina, but the effects are infrequently documented. This study provides information that will contribute to greater understanding of how watersheds respond to these events.}, number={6}, journal={Transactions of the ASAE}, author={Shelby, J. D. and Chescheir, G. M. and Skaggs, R. W. and Amatya, D. M.}, year={2005}, pages={2179–2188} }
 @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{skaggs_chescheir_2003, title={Effects of subsurface drain depth on nitrogen losses from drained lands}, volume={46}, DOI={10.13031/2013.12974}, abstractNote={A simulation study was conducted to determine effects of drain depth on nitrogen (N) loss in drainage water. 
Simulations were conducted for drain depths of 0.75, 1.0, 1.25, and 1.5 m for a Portsmouth sandy loam at Plymouth, North 
Carolina. A wide range of drain spacing was considered for each depth. Corn yields were predicted and an economic analysis 
was conducted to determine the drain spacing giving maximum predicted profit for each depth. Results showed that nitrogen 
losses from subsurface drains can be reduced by placing the drains at shallow depths. In order to satisfy agricultural 
production requirements, shallow drains must be placed closer together than deeper drains. While predicted agricultural 
profits for the shallow drains are reduced somewhat compared to the deeper drains, overall profits are substantially increased 
when the cost of removing N from drainage water is considered.}, number={2}, journal={Transactions of the ASAE}, author={Skaggs, R. W. and Chescheir, G. M.}, year={2003}, pages={237–244} }
 @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{appelboom_chescheir_skaggs_hesterberg_2002, title={Management practices for sediment reduction from forest roads in the coastal plains}, volume={45}, DOI={10.13031/2013.8529}, abstractNote={Sediment has been identified as one of the most important non-point source pollutants of surface waters. In forested areas, the predominant source of sediment is from the construction and maintenance of access roads, which contribute as much as 90% of the total eroded sediments. Seven different road management practices were studied to determine their effectiveness in reducing sediment production from forest roads on nearly flat lands in the lower coastal plains of North Carolina. One practice utilized a continuous berm along the roadside, while the other six practices had a non-continuous berm with different combinations of road surface gravel and roadside vegetative strips. Runoff samples collected during eleven different rainfall events of varying intensity and duration were analyzed for sediment content. The rainfall amount, intensity, infiltration, and antecedent rainfall conditions were combined into a single energy rating to assist in the overall analysis. The results of the study showed that a continuous berm maintained along the edge of a forest road can reduce total sediment loss by an average of 99% compared to the same type road without the presence of a continuous berm. When a continuous berm is not present, graveling the road surface can reduce the total loss of sediment from roads by an average of 61% compared to a non-graveled road surface. A 90 cm wide grass strip on the edge of the driving surface can reduce total sediment loss by an average of 56% compared to a road without a grass strip.}, number={2}, journal={Transactions of the ASAE}, author={Appelboom, T. W. and Chescheir, G. M. and Skaggs, R. W. and Hesterberg, Dean}, year={2002}, pages={337–344} }
 @article{fernandez_chescheir_skaggs_amatya_2002, title={Watgis: A GIS-based lumped parameter water quality model}, volume={45}, DOI={10.13031/2013.8822}, abstractNote={A Geographic Information System (GIS)-based, lumped parameter water quality model was developed to estimate the spatial and temporal nitrogen-loading patterns for lower coastal plain watersheds in eastern North Carolina. The model uses a spatially distributed delivery ratio (DR) parameter to account for nitrogen retention or loss along a drainage network. Delivery ratios are calculated from time of travel and an exponential decay model for in-stream dynamics. Travel times from any point in the drainage network to the watershed outlet are obtained from simulations using a combined physically based field hydrology and drainage canal routing model (DRAINMOD-DUFLOW). Nitrogen load from contributing areas in the watershed delivered to the main watershed outlet is obtained as the product of field export with the corresponding delivery ratio. The total watershed load at the outlet is the combined loading of the individual fields. Nitrogen exports from source areas are measured. The lumped water quality model is integrated within a GIS framework with menu interface, display options, and statistical procedures. Within this framework, the model can be used as a screening tool to analyze the effects of different land and water management practices on downstream water quality. A description of the model is presented along with the results from the evaluation of the model to characterize the seasonal and annual export of nitrogen from a drained forested watershed near Plymouth, North Carolina. Results of the study showed that the lumped parameter model can reasonably predict the loads at the outlet of the watershed. Predicted loads for 1997 were highly correlated with the observed loads (correlation coefficients of 0.99, 0.90, and 0.96 for nitrate-nitrogen, TKN, and total nitrogen respectively). Sensitivity and uncertainty analyses indicated that predicted outlet loads were sensitive to field flow predictions and export concentrations. Overall, the results indicate that the lumped parameter model can be an effective tool for describing the monthly nitrogen loads from a poorly drained coastal plain watershed.}, number={3}, journal={Transactions of the ASAE}, author={Fernandez, G. P. and Chescheir, G. M. and Skaggs, R. W. and Amatya, D. M.}, year={2002}, pages={593–600} }
 @article{luo_skaggs_chescheir_2001, title={DRAINMOD modifications for cold conditions}, volume={43}, ISBN={0001-2351}, DOI={10.13031/2013.3057}, abstractNote={The field hydrology model DRAINMOD was modified to include freezing and thawing, and snowmelt 
components. Based on daily hydrologic predictions of the original model, the modified DRAINMOD numerically solves 
the heat flow equation to predict soil temperature. When freezing conditions are indicated by below zero temperatures, the 
model calculates ice content in the soil profile and modifies soil hydraulic conductivity and infiltration rate accordingly. 
Recorded precipitation is separated as rain and snow when daily average air temperature is above or below a rain/snow 
dividing base temperature. Snow is predicted to accumulate on the ground until air temperature rises above a snowmelt 
base temperature. Soil surface temperature is recalculated when snow cover exists. Daily snowmelt water is added to 
rainfall, which may infiltrate or run off depending on soil freezing condition. The modified DRAINMOD predictions of 
soil temperature agreed well with field observations at Plymouth, North Carolina, Truro, Nova Scotia, and Lamberton, 
Minnesota. Assuming air temperature as the soil surface boundary condition increased the variability of soil temperature 
predictions at shallow depths, agreement with field measurements was still good. The method of using average air 
temperature as an indicator to separate snow and rain worked very well for Carsamba, Turkey. At Truro, Nova Scotia, 
however, the method was not as successful, and several snow events were predicted as rainfall and vice versa. Compared 
with the original version of DRAINMOD, the modified version predicts fewer drainage flow events in winter months 
because of snow accumulation on the surface. Subsurface drainage and/or surface runoff resulting from snowmelt are 
predicted when air temperature rises, the snow melts, and the soil begins to thaw.}, number={6}, journal={Transactions of the ASAE}, author={Luo, W. and Skaggs, R. W. and Chescheir, G. M.}, year={2001}, pages={1569–1582} }
 @inbook{skaggs_chescheir_1999, title={Application of simulation models}, DOI={10.2134/agronmonogr38.c16}, abstractNote={This chapter reports approaches to develop crop-water production functions under saline conditions and discusses the factors which affect the production functions. Some examples are given illustrating the interaction between irrigation and drainage. The irrigation-drainage interaction is characterized by the function between applied water and deep percolation. Irrigation and drainage are inseparably linked. Since the major irrigated areas are located in arid and semiarid regions of the world, salinity becomes a significant factor in the interrelationship between irrigation, drainage, and crop production. An array of models is available to simulate the effects of irrigation water salinity, irrigation uniformity, and irrigation scheduling on crop yield and deep percolation. The seasonal model is particularly useful in producing crop-water production functions which account for both salinity and irrigation uniformity for conditions where the water table does not contribute significantly to the water supply of the crop.}, booktitle={Agricultural drainage: Chapter 15  (Agronomy ; no. 38).}, publisher={Madison, Wis.: American Society of Agronomy, Inc.: Crop Science Society of America, Inc.: Soil Science Society of America, Inc.}, author={Skaggs, R. W. and Chescheir, G. M.}, editor={R.W. Skaggs and Schilfgaarde, J.Editors}, year={1999}, pages={537–564} }
 @inproceedings{fernandez_chescheir_amatya_skaggs_1999, title={GIS-based water quality lumped parameter model}, number={1999}, booktitle={Proceedings of the Mini-Conference, Advances in Water Quality Modeling}, publisher={St. Joseph, MI: ASAE}, author={Fernandez, G.P. and Chescheir, G.M. and Amatya, D.M. and Skaggs, R.W.}, year={1999}, pages={65–70} }
 @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} }
 @inproceedings{amatya_chescheir_fernandez_skaggs_1999, title={Testing of a watershed scale hydrologic/water quality model for poorly drained soils}, number={1999}, booktitle={Proceedings of the Mini-Conference, Advances in Water Quality Modeling}, publisher={St. Joseph, MI: ASAE}, author={Amatya, D. M. and Chescheir, G. M. and Fernandez, G. P. and Skaggs, R. W.}, year={1999}, pages={33–39} }
 @inbook{fernandez_skaggs_chescheir_amatya_1999, title={Watershed scale GIS based lumped parameter water quality model}, booktitle={Proceedings of 2nd Inter-Regional Conference on Environment-Water, Emerging Technologies for Sustainable Land Use and Water Management}, publisher={Lausanne, Switzerland: Presses Polytechniques et Universitaries Romandes}, author={Fernandez, G. P. and Skaggs, R. W. and Chescheir, G. M. and Amatya, D. M.}, editor={L. Amusy, S. Periera and Fritsch, M.Editors}, year={1999} }
 @inproceedings{fernandez_chescheir_skaggs_1998, title={DRAINMOD 5.0: A Windows version that considers crop yield, nitrogen and salinity}, 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={Fernandez, G. P. and Chescheir, G. M. and Skaggs, R. W.}, year={1998}, pages={220–226} }
 @inproceedings{amatya_chescheir_skaggs_fernandez_birgand_1998, title={Evaluation of a DRAINMOD based watershed scale model}, 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={Amatya, D. M. and Chescheir, G. M. and Skaggs, R. W. and Fernandez, G. and Birgand, F.}, year={1998}, pages={211–219} }
 @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{chescheir_skaggs_gilliam_1992, title={Evaluation of wetland buffer areas for treatment of pumped agricultural drainage water}, volume={35}, DOI={10.13031/2013.28585}, abstractNote={A computer method was developed for predicting nutrient and sediment removal from agricultural drainage water pumped onto wetland buffer areas. The method utilizes a model for simulating drainage from agricultural land and a model for simulating overland flow, and nutrient and sediment removal on wetlands. Both simulation models were calibrated using data collected in field experiments. The simulation models were then coupled to predict the percent removal of sediment, total phosphorus (P), total Kjeldahl nitrogen (TKN), and nitrate nitrogen (NO3-N) from drainage water for a 20-year period of climatological data. This method predicted that the 240 ha wetland buffer at the field research site could be expected to remove over 79% of the TKN, NO3-N, P, and sediment in drainage water from a 1250 ha agricultural watershed. The method was used to evaluate the effects of buffer size and shape on the nutrient and sediment removal effectiveness of the wetland.}, number={1}, journal={Transactions of the ASAE}, author={Chescheir, G. M. and Skaggs, R. W. and Gilliam, J. W.}, year={1992}, pages={175} }