Browsing by Author "Dr. J.W. Gilliam, Committee Member"

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    The Effect of Shallow Subsurface Drains on Nitrate-N and Orthophosphorus Losses from Drained Agricultural Lands
    (2006-05-10) Poole, Chad; Dr. R.W. Skaggs, Committee Co-Chair; Dr. G.M. Chescheir, Committee Co-Chair; Dr. J.W. Gilliam, Committee Member
    Field and modeling studies were conducted to determine the effect of subsurface drain depth on nitrate and orthophosphorus losses in drainage effluent. The field research was conducted on a site located near Plymouth, NC at the Tidewater Research Station. The soil at the site is a Cape Fear loam. Two drainage systems were installed on a 2.5 ha pasture which was used for grazing beef cattle. The pasture was under a Bermuda-Rye rotation during the study period. Each drain plot consisted of five- 125 m drain lines 10 cm in diameter. The average depth for plot 1 was 1.44 m at 25 m spacing. Plot 2 had an average depth of 0.70 m at 12.5 m spacing. Precipitation, water table depths, and subsurface drainage rates were measured during the 31-month study period from October 1, 2002 through April 30, 2005. Subsurface drainage and shallow groundwater were sampled and analyzed to determine nitrate and orthophosphorus concentrations. Outflows from the shallow drains were 17.1 % less than from the deep drains for the 31-month period. Rainfall was average to well above average for the majority of the study period. An analysis of variance (ANOVA) showed that cumulative drainage volumes from the shallow drains were significantly less from that of the deep drains in only 2004 and 2005. High water tables in both plots resulted from the average to well above average precipitation during the study. Average nitrate concentrations in the groundwater at 90-120 cm, 150-180 cm and 210-240 cm were significantly lower for the shallower drains than for the deeper drains. The average concentrations in the drainage water for nitrate were not significantly different between the treatments. Plot 1 averaged 6.1 mg⁄L and Plot 2 averaged 6.6 mg⁄L. Nitrate export by the shallow drains was 9.8 % less than from the deeper drains. Exports from the two plots were not significantly different when the average cumulative values for each year, or partial year were compared using analysis of variance (ANOVA). However, when export values were analyzed by month (under similar weather patterns) and then compared with a paired two-sample t-test for means, the shallow system did significantly reduce nitrate export between the two systems. Orthophosphorus concentrations in the groundwater at 90-120 cm, 150-180 cm and 210-240 cm were significantly higher for the shallower drains than for the deeper drains. The average concentrations in the drainage water for orthophosphorus were significantly higher for the shallow plots. Plot 2 averaged 0.43 mg⁄L and Plot 1 averaged 0.24 mg⁄L. Orthophosphorus export was increased during the course of the study by the shallow system by 103 %. The export was significantly different when the average cumulative values for each plot were compared using ANOVA and when monthly values were compared using a paired two-sample t-test. Long-term (72-year) simulations using DRAINMOD predicted that yearly drainage volumes from the shallow plot were significantly less than from the deep plot at the 10% level. The average yearly reduction in drainage volume was approximately 24 %. The simulated predicted average yearly reduction in nitrate losses was 22 %. Analysis of variance showed that Plot 2 exported significantly less nitrate than Plot 1 at the 10 % level with a p-value of <0.0001 for the 72 years of simulated data. On a cumulative basis, the shallow system reduced predicted nitrate loss by approximately 22 %. The average yearly predicted losses of orthophosphorus from the deep system was 1.0 kg/ha while from the shallow system it was 1.5 kg/ha, an average increase of 0.5 kg⁄ha. This implies an average yearly increase in orthophosphorus losses of 50 %. The ANOVA analysis showed that Plot 2 exported significantly more OP than Plot 1 at the 10% level over the 72 years simulated. On a cumulative basis for the 72-year simulation period, the shallow system increased orthophosphorus export by 40.3 %. The long-term simulations show that the shallow system will export on average between 40 to 50 % more orthophosphorus than the deeper system.
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    Effects of In-Stream Processes on the Fate of Nitrogen and Phosphorous in Drainage Canals of Forested Watersheds
    (2004-05-11) Appelboom, Timothy William; Dr. G.M. Chescheir, Committee Co-Chair; Dr. R.W. Skaggs, Committee Co-Chair; Dr. J.W. Gilliam, Committee Member; Dr. D.M. Amatya, Committee Member; Dr. H.R. Malcom, Committee Member
    As time progressed and populations increased, human activities related to the production of resources such as food, timber, clothing, and energy have focused on enhancing biological systems to increase yields. This has resulted in the altering of the natural cycles of nitrogen and phosphorous throughout the world. The objectives of this study were to; 1. conduct a literature review of forest stream hydrologic and nutrient inputs, outputs, and transformations and their associated contributions to the overall budgets, 2. quantify these inputs, outputs, and transformations for a drainage network section in the lower coastal plain of North Carolina, and 3. develop a mathematical relationship to describe nitrate removal from forest drainage systems that can be used in modeling. Upstream inflow, rainfall/throughfall, and subsurface flow along with litterfall and lateral movement were measured as inputs, outflow at the outlet and denitrification were measures as outputs to the drainage section. Denitrification was estimated using seven methods; in stream tanks, undisturbed cores, background N15 and O18 concentrations, N15 enrichment, diffusion calculations, mass balance, and modeling. During this study, 6.7 kg of nitrate was removed through demitrification during the first years flow period (85 days) and 19.8 kg dur4ing the second years flow period (82 days) from the 1900 meter log and 3 meter wide drainage canal section studied. The mathematical relationship to describe the nitrate removal rate is based on a depth and concentration independent term which takes temperature into account. This relationship is based on a term called a mass transfer coefficient (r). This relationship resulted in a mass transfer coefficient (r) of 0.064 m/day at 25oC.