VTechWorks Repository :: Browsing by Author "Dillaha, Theo A. III"

Browsing by Author "Dillaha, Theo A. III"

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Agricultural BMP Placement for Cost-effective Pollution Control at the Watershed Level
Veith, Tamie L. (Virginia Tech, 2002-02-11)
The overall goal of this research was to increase, relative to targeting recommendations, the cost-effectiveness of pollution reduction measures within a watershed. The goal was met through development of an optimization procedure for best management practice (BMP) placement at the watershed level. The procedure combines an optimization component, written in the C++ language, with spatially variable nonpoint source (NPS) prediction and economic analysis components, written in the ArcView geographic information system scripting language. The procedure is modular in design, allowing modifications or enhancements to the components while maintaining the overall theory. The optimization component uses a genetic algorithm to optimize a lexicographic multi-objective function of pollution reduction and cost increase. The procedure first maximizes pollution reduction to meet a specified goal, or maximum allowable load, and then minimizes cost increase. For the NPS component, a sediment delivery technique was developed and combined with the Universal Soil Loss Equation to predict average annual sediment yield at the watershed outlet. Although this evaluation considered only erosion, the NPS pollutant fitness score allows for evaluation of multiple pollutants, based on prioritization of each pollutant. The economic component considers farm-level public and private costs, accounting for crop productivity levels by soil and for enterprise budgets by field. The economic fitness score assigns higher fitness scores to scenarios in which costs decrease or are distributed more evenly across farms. Additionally, the economic score considers the amounts of cropland, hay, and pasture needed to meet feed and manure/poultry litter spreading requirements. Application to two watersheds demonstrated that the procedure optimized BMP placement, locating scenarios more cost-effective than a targeting strategy solution. The optimization procedure identified solutions with lower costs than the targeting strategy solution for the same level of pollution reduction. The benefit to cost ratio, including use of the procedure and implementation of resulting solutions, was demonstrated to be greater for the optimization procedure than for the targeting strategy. The optimization procedure identifies multiple near optimal solutions. Additionally, the procedure creates and evaluates scenarios in a repeated fashion without requiring human interaction. Thus, more scenarios can be evaluated than are feasible to evaluate manually.
Agricultural BMPs applicable to Virginia
Heatwole, Conrad D.; Dillaha, Theo A. III; Mostaghimi, Saied (Virginia Water Resources Research Center, Virginia Polytechnic Institute and State University, 1991-03)
Agronomic and Nitrate Leaching Impacts of Pelletized versus Granular Urea
Shah, Sanjay Bikram (Virginia Tech, 2000-08-02)
Agronomic and water quality impacts of urea particle size were evaluated through field and laboratory experiments and mathematical modeling. In a two-year field study, corn silage yield, corn nitrogen (N) removal, and nitrate-N (NO₃⁻-N) leaching from urea pellets (1.5 g each) and granules (0.01-0.02 g each) applied at 184 kg-N/ha were compared. A control treatment (no N) and two other N application rates (110 and 258 kg-N/ha) were also included. Urea particle size impact on dissolution rate, dissolved urea movement, mineralization, and N0³-N leaching were evaluated in the laboratory. A two-dimensional (2-D) mathematical model was developed to simulate the fate of subsurface-banded urea and its transformation products, ammonium (NH₄⁺)and NO₃⁻. With 184 kg-N/ha, corn silage yield was 15% higher (p = 0.02) and corn N removal was 19% higher (p = 0.07) with pellets than granules in the second year of the field study. In the absence of yield response at 110 kg-N/ha, reason for higher yield at 184 kg-N/ha with pellets was unclear. Greater N removal reduced NO₃⁻-N leaching potential from pellets compared to granules during the over-winter period. No urea form response to yield or corn N removal was observed in the first year. In 23 of 27 sampling events, granules had higher NO₃⁻-N concentration in the root zone than pellets, with average nitrate-N concentrations of 2.6 and 2.2 mg-N/L, respectively. However, statistically, NO₃⁻-N leaching from the root zone was unaffected by urea form, probably due to high variability within treatments masking the treatment effects. In October 1997, pellets retained 16% more (p = 0.04) inorganic-N in the top half of the root zone than granules, due to slower nitrification in pellets as was determined in the mineralization study. Slower NO₃⁻-N leaching allowed for greater N extraction by plants. Pellets had lower dissolution, urea hydrolysis, and nitrification rates than granules; however, nitrification inhibition was the dominant mechanism controlling N fate. The model took into account high substrate concentration effects on N transformations, important for simulating the fate of band-applied N. The model exhibited good mass conservative properties, robustness, and expected moisture and N distribution profiles. Differences in measured field data and model outputs were likely due to uncertainties and errors in measured data and input parameters. Model calibration results indicated that moisture-related parameters greatly affected N fate simulation. Sensitivity analyses indicated the importance of nitrification-related parameters in N simulation, particularly, their possible multiplicative effects. Need for extensive model testing and validation was recognized. The validated 2-D N model could be incorporated into a management model for better management of subsurface-banded granular N. However, the 2-D model is not appropriate for simulating the three dimensional N movement from pellets.
Ammonia Emissions from Dairy Manure Storage Tanks Affected by Diets and Manure Removal Practices
Li, Lifeng (Virginia Tech, 2009-08-07)
The objectives of this study were to determine: 1) ammonia emission rates from stored scraped and flushed manure from dairy cows fed either normal or low N diet; and 2) seasonal effects on ammonia emission rates from stored scraped and flushed dairy manure. Four pilot-scale tanks were used for manure storage with different treatments - scraped manure for normal diet (NS), flushed manure for normal diet (NF), scraped manure for low N diet (LS), and flushed manure for low N diet (LF). The first part of the study lasted for 1 month and four treatments were all investigated; the second part of the study lasted for 12 months and two tanks with treatments NS and NF were investigated. Dynamic flux chambers and a photoacoustic gas analyzer were used to measure ammonia emission rates. There was no significant change of the N content of manure as the dietary N content is reduced (from 17.8% to 15.9% crude protein). However, ammonia emission rates from manure storage tanks were reduced by 33% (from 27.4 ± 38.1 to 18.4 ± 21.9 mg m⁻²h⁻¹; P<0.0001 based on paired t-test). Flushing manure reduced emission rates by 72% compared to scraping manure (from 35.6 ± 39.6 to 10.1 ± 8.2 mg m⁻²h⁻¹; P<0.0001 based on paired t-test). Ammonia emission rates for NS, NF, LS and LF were 43.9 ± 48.0, 10.9 ± 8.7, 27.4 ± 27.3, and 9.3 ± 7.8 mg m-2 h-1, respectively. The chamber headspace temperature for NS, NF, LS and LF were 26.0 ± 6.9, 25.8 ± 6.8, 26.6 ± 6.5, and 27.2 ± 6.7 °C, respectively. The manure pH for NS, NF, LS, and LF were 6.3 ± 0.1, 6.4 ± 0.3, 6.4 ± 0.1, and 6.1 ± 0.1, respectively. Both dietary N reduction and manure flushing are recommended to reduce ammonia emission rates from dairy manure storage tanks. Ammonia emission rates were higher in summer and fall, due to higher air temperature and higher manure pH. The pH of scraped manure was 7.2 ± 0.6, 6.7 ± 0.2, 6.5 ± 0.3 and 7.0 ± 0.3 for fall, winter, spring and summer, respectively. The pH of flushed manure was 6.8 ± 0.4, 6.7 ± 0.4, 6.4 ± 0.3 and 6.8 ± 0.4 for fall, winter, spring and summer, respectively. Ammonia emission rates from scraped manure for fall, winter, spring, and summer were 7.4 ± 8.6, -0.5 ± 1.2, 1.1 ± 1.9, and 5.8 ± 2.7 mg m⁻²h⁻¹, respectively. Ammonia emission rates from flushed manure for fall, winter, spring, and summer were 3.9 ± 4.2, -0.5 ± 0.9, 0.8 ± 1.4, and 4.4 ± 1.2 mg m⁻²h⁻¹, respectively. Seasonal changes of air temperature and manure pH were key factors affecting ammonia emissions from manure storage in this study. Seasonal climate conditions including precipitations (rainstorms and snows) and icing can cause reduction of ammonia emissions from manure storage in open air. More attention should be paid to reduce ammonia emissions in warmer seasons, e.g., by covering the storage facilities.
Areal Modeling of Erosion for Environmental Nonpoint Applications (AMEENA)
Al-Smadi, Mohammad Ahmed (Virginia Tech, 2007-08-10)
Erosion and sediment delivery from upland areas to waterbodies is a major problem impacting water quality in the United States and elsewhere. Measures to reduce these impacts are either targeted at reducing erosion on-site or at reducing delivery of sediment to waterbodies. AMEENA (Areal Modeling of Erosion for Environmental Nonpoint Applications) is a spatially distributed model that estimates erosion and deposition on a watershed scale by predicting erosion and transport over the landscape surface. Erosion is predicted based on the Revised Universal Soil Loss Equation (RUSLE), and sediment transport capacity is estimated as a function of upslope flow volume, local gradient, and land use. Gross erosion is routed to edge-of-stream with a routing algorithm that iteratively compares available sediment with transport capacity on a cell by cell basis from ridge cells to stream cells. The model is implemented completely within a raster GIS to facilitate use of the model as a tool to readily evaluate impact of land use practices on sediment delivery to streams. AMEENA was validated using field data of net erosion and sediment deposition from three field studies. AMEENA predicted the spatial distribution of net erosion and deposition better than WaTEM/SEDEM which is a distributed parameter erosion model based on a similar modeling approach. AMEENA's suitability to simulate the impact of management practices such as filter strips and critical area planting was evaluated on plot (profile) scale and catchment scale simulations. Results of plot scale simulations were intuitive and the model proved more reasonable for these scenarios than did RUSLE2 and WEPP. The catchment scale study highlighted features of AMEENA that are not available in RUSLE2 and WEPP in terms of identifying erosion “hot spots” and the ability to utilize the explicit sediment flow path identification in locating best placement of off-site sediment control measures. Since AMEENA does not account for in-stream erosion processes, it is not suitable for simulating areas dominated by channel or gully erosion.
An Assessment of the Quality of Agricultural Best Management Practices in the James River Basin of Virginia
Cunningham, Janelle Hope (Virginia Tech, 2003-08-21)
Assessment tools were developed to address the need for a low cost, rapid method of quantifying the quality of agricultural best management practices (BMPs). Best management practices are either cost-shared, where some or all of the capital costs of the practice were subsidized with federal, state, or local funds, or non cost-shared, where the cost of the practice and its upkeep is paid for by the landowner or farm operator. Cost-share practices are required to comply with state standards, while non cost-share practices are not subject to any standards. For this study, BMP quality is defined as the adherence to design, site selection, implementation, and maintenance criteria relating to water quality as specified by state and federal agencies promoting BMP implementation. The two objectives of this research were: 1. develop a set of assessment tools to quantify the quality of agricultural best management practices in a rapid low-cost manner, and 2. test the tools and determine if differences in quality exist between cost-share and non cost-share BMPs in the James River Basin of Virginia. Assessment tools were developed for sixteen practices: alternative water systems, stream fencing, streambank stabilization, grass filter strips, wooded buffers, permanent vegetative cover on critically eroding areas, permanent vegetative cover on erodible cropland, reforestation of erodible crop and pasture land, animal waste storage facilities, grazing land protection systems, loafing lot management systems, late winter split application of nitrogen on small grains, protective cover for specialty crops, sidedress application of nitrogen on corn, small grain cover crops-fertilized and harvested, and small grain cover crops for nutrient management. Assessment tools were developed using both Virginia BMP standards and expert knowledge. Virginia Department of Recreation and Conservation (DCR) and Virginia and national Natural Resource Conservation Service (NRCS) BMP standards were collected and sorted into the four quality component categories; design, site selection, implementation, and maintenance. Standards that pertained directly to a BMPs' potential to protect water quality were translated into question format. Multiple-choice or yes/no questions were used as often as possible to avoid potential bias and for ease of processing. Assessment tool development involved an iterative process that included input from a research team (university-based researchers) and an expert team (public and private sector professionals and practitioners responsible for BMP design and assessment). One hundred and fifty-five cost-shared BMPs and 150 non cost-shared BMPs were assessed on 128 independent farms in the James River Basin of Virginia over a period of four months. The assessment tools were loaded onto a personal digital assistant (PDA), which facilitated data collection and eliminated the need for data transcription. Data collected on the PDA were uploaded periodically to a computer database. A digital camera was used to develop a photographic record of the assessed BMPs. Best management practice quality scores were based on five-point scale, with one being the lowest quality score and five as the highest. Statistical analyses conducted on both the overall quality scores and the quality component scores, indicate that there is not a strong significant difference (p = 0.05) in quality between the cost-shared and non cost-shared BMPs assessed for this study. Statistically significant differences between cost-share and non cost-share practices did, however, exist. For the filter/buffer strips practices (grass filter strips and wooded buffers), the implementation quality component cost-share mean (3.35) and the non cost-share mean (3.88) were statistically different at the 0.05 level (p-value = 0.026). One other statistically significant difference was found. For stream fencing, the overall quality cost-share mean was 4.68 while the non cost-share mean was 4.20; the means are statistically different at the 0.05 level (p-value = 0.043). Statistical analyses were performed to determine if age of practice, farm size, or Soil and Water Conservation District (SWCD) had effects on the BMP quality. No statistically significant differences (p = 0.05) were found relating to the age of an assessed BMP or farm size. One SWCD, the Robert E. Lee district, had a statistically significant difference in the design quality component means; cost-share mean = 4.21, non cost-share mean = 2.94 with a p-value of 0.048. The statistically significant differences that were detected do not establish a clear trend; it appears that for the BMPs assessed here the qualities of cost-share and non cost-share practices are roughly equal. The fact that cost-share practices and non cost-share practices do appear to be roughly equal may be the result of education and outreach programs sponsored by Virginia's SWCDs and Virginia Cooperative Extension. Non cost-share practices may be of equal quality to cost-share practices because those implementing BMPs without the benefit of cost-share may have a greater stake (both financial and personal) in those practices performing well. If no statistically significant difference in quality exists between cost-share and non cost-share practices, then non cost-share practices should be treated equally when accounting for BMPs in NPS pollution in watershed management and computer modeling. Currently, only cost-share practices are included in computer models, in part because these are the only practices tracked by the existing BMP establishment infrastructure. Estimating the numbers and distribution of non cost-share practices and incorporating them into NPS water quality modeling efforts will more accurately reflect the steps agricultural producers have and are taking to decrease the amount of NPS pollution reaching water bodies. Additionally, policy regarding NPS pollution and BMPs should reflect the apparent equal qualities of cost-share and non cost-share practices. The assessment tools developed as a part of this study can potentially be applied to determine the quality of BMPs on basin or state-wide scales to give policy makers a better understanding of the practices and populations that the policies are created for. Moreover, BMP quality scores have the potential to be used as a surrogate measure for BMP performance. Further research recommendations include correlating BMP quality scores with BMP performance, wider scale testing of the tools, continued revision of the tools, and using the assessment tool scores to diagnose BMP quality problems.
Auxiliary Procedures for the AGNPS Model in Urban Fringe Watersheds
Yagow, Eugene R. (Virginia Tech, 1997-02-28)
The Agricultural Nonpoint Source model (AGNPS) is a single-event grid-based model used for simulating runoff, sediment and nutrients from agricultural areas. This study involved using geographic information system (GIS) spatial data and functionality to improve the spatial and temporal assignment of parameter values for the AGNPS 5.0 model and incorporated methods for representing urban fringe land uses and their nonpoint source (NPS) pollution contributions in model inputs. Auxiliary procedures for modeling with AGNPS were developed both for enhancing input into the model and for enhancing modeled output. On an event basis, one procedure automated the creation of complex-formatted AGNPS 5.0 model input files using GIS as a spatial data manager. One pair of alternative procedures were developed to automate the assignment of parameter values on an event basis. One procedure used typical average annual parameter values, and the second assigned parameter values using adaptations of existing time-dependent relationships. On a monthly basis, a sequencing procedure was created to perform multiple runs with the model for a list of storms while updating parameters for each event and aggregating monthly modeled spatial output. Another pair of alternative procedures were developed to facilitate the simulation of monthly output from AGNPS modeled events. The first of these aggregated event output for all storms in each month, while the second supplemented the aggregated output with baseflow and septic system loads. The study area was the 6,500 ha urbanizing Bull Run watershed in northern Virginia, which was modeled as 14,621 cells. Databases were assembled and 109 selected storm events within a 16-year period were modeled using the above procedures. Event data were added together, where necessary, to correspond with observed data from composite-sampled intervals. Output from the two event parameterization procedures were compared with monitored loads calculated for 89 composite periods, while output from the two monthly simulation procedures were compared with monthly monitored data for 23 complete months. The monitored-modeled comparisons were considered inconclusive. Evidence strongly suggested that the rainfall records from a rain gauge outside the watershed did not correspond well with monitored runoff. The average runoff produced with the AGNPS model from the 109 selected storms amounted to 40.7% of rainfall, consistent with the calculated long-term average of 38% for the Bull Run watershed. A nonpoint source pollution index was developed to utilize monthly modeled total nitrogen, total phosphorus, and suspended sediment. Individual rating curves were developed to separately transform loads and concentrations of each pollutant into sub-index values. The maximum sub-index from each parameter was added together and averaged for the index. The index was calculated at the watershed outlet from monitored data, and in a spatially-distributed fashion along all streams from simulated output.
Bacteria Total Maximum Daily Load Issues: Report of the Bacteria TMDL Subcommittee of the Water Quality Academic Advisory Committee
Dillaha, Theo A. III; Hershner, Carl H.; Kator, Howard I.; Mostaghimi, Saied; Shabman, Leonard A.; Smith, Eric P.; Younos, Tamim M.; Zipper, Carl E. (Virginia Water Resources Research Center, 2002-10)
Comparison of 1-D and 2-D modeling approaches for simulating runoff and sediment transport in overload areas
Hong, Seonggu (Virginia Tech, 1995-10-26)
One-dimensional and two-dimensional modeling approaches were compared for their abilities in predicting overland runoff and sediment transport. Both the I-D and 2-D models were developed to test the hypothesis that the 2-0 modeling approach could improve the model predictions over the 1-0 approach, based on the same mathematical representations of physical processes for runoff and sediment transport. Runoff processes were described based on the St. Venant equations and the sediment transport was based on the continuity relationship. The finite element method was employed to solve the governing equations. The nonlinear, time-dependent system of equations obtained by the finite element formulation was solved by the substitution method and the implicit method. The models were verified by comparing the analytical solutions presented by Singh and Regl (1983) and the solution by the Izzard method (Chow, 1959). The comparison showed that both the 1-0 and 2-D models provided reasonable estimations of runoff and sediment loadings. Evaluation of the models was based on four different hypothetical case studies and two experimental studies. The hypothetical case studies investigated the effects of the discretization level, cross slopes, and the size of the field area on the model predictions. The two experimental studies provided a comparison of model predictions with observed data. The results of the hypothetical case studies indicated that the maximum differences in the model predictions at the outlet were about 30% between the two modeling approaches. When the discretization level was sufficient to reasonably describe the shape of the surface, the 1-0 model prediction were almost the same as the 2-D model predictions. Even though cross slopes existed in the field, the differences in the model predictions at the outlet were not significant between the 1-0 and 2-0 models. The differences in the model predictions of runoff and sediment loading were not affected by the changes in the size of the field. Since the 2-D model resulted in 10 to 20% differences in model predictions when different boundary conditions were used and the 1-D model predictions were also affected by the choice of element length, the differences in model predictions at the outlet, shown in model application results, which were less than 30% in most cases, could not be considered significant. The model applications to the experimental studies also showed that no substantial differences existed in the model predictions between the I-D and 2-D models. Even though the spatial distributions of the flow depth and sediment concentration were significantly different, runoff volumes and sediment yields at the outlet showed less than 10% differences. Compared with the I-D model, the 2-D model required much more computational time and effort to simulate the same problems. In addition, convergence problems due to negative flow depths limited the 2-D model applications. The 2-D simulations required more than twice the computational time needed for the I-D simulations. As long as the model predictions at the outlet are concerned, the much greater computational costs and efforts could not justify the use of the 2-D approach. Based on the simulation results from the selected hypothetical case and experimental studies, the 2-D model provided better representations of spatial distribution of flow depths and sediment concentrations than the I-D model. However, no substantial differences in predictions of total runoff volume and sediment yield at the outlet area were found between the I-D and 2-D models.
Comparison of Two Algorithms for Removing Depressions and Delineating Flow Networks From Grid Digital Elevation Models
Srivastava, Anurag (Virginia Tech, 2000-02-10)
Digital elevation models (DEMs) and their derivatives such as slope, flow direction and flow accumulation maps, are used frequently as inputs to hydrologic and nonpoint source modeling. The depressions which are frequently present in DEMs may represent the actual topography, but are often the result of errors. Creating a depression-free surface is commonly required prior to deriving flow direction, flow accumulation, flow network, and watershed boundary maps. The objectives of this study were: 1) characterize the occurrence of depressions in 30m USGS DEMs and assess correlations to watershed topographic characteristics, and 2) compare the performance of two algorithms used to remove depressions and delineate flow networks from DEMs. Sixty-six watersheds were selected to represent a range of topographic conditions characteristic of the Piedmont and Mountain and Valley regions of Virginia. Analysis was based on USGS 30m DEMs with elevations in integer meters. With few exceptions watersheds fell on single 7.5minute USGS quadrangle sheets, ranged in size from 450 to 3000 hectares, and had average slopes ranging from 3 to 20 percent. ArcView (3.1) with the Spatial Analyst (1.1) extension was used to summarize characteristics of each watershed including slope, elevation range, elevation standard deviation, curvature, channel slope, and drainage density. TOPAZ (ver 1.2) and ArcView were each used to generate a depression-free surface, flow network and watershed area. Characteristics of the areas 'cut' and 'filled' by the algorithms were compared to topographic characteristics of the watersheds. Blue line streams were digitized from scanned USGS 7.5minute topographic maps (DRGs) then rasterized at 30 m for analysis of distance from the derived flow networks. The removal of depressions resulted in changes in elevation values in 0 - 11% of the cells in the watersheds. The percentage of area changed was higher in flatter watersheds. Changed elevation cells resulted in changes in two to three times as many cells in derivative flow direction, flow accumulation and slope grids. Mean fill depth by watershed ranged from 0 to 10 m, with maximum fill depths up to 40 m. In comparison with ArcView, TOPAZ, on average affected 30% fewer cells with less change in elevation. The significance of the difference between ArcView and TOPAZ decreased as watershed slope increased. A spatial assessment of the modified elevation and slope cells showed that depressions in the DEMs occur predominantly on or along the flow network. Flow networks derived by ArcView and TOPAZ were not significantly different from blue line streams digitized from the USGS quadrangles as indicated by a paired t test. Watershed area delineated by ArcView and TOPAZ was different for almost all watersheds, but was generally within 1%. Conclusions from this study are: 1) The depressions in 30 m DEMs can make up a significant portion of the area especially for flatter watersheds; 2) The TOPAZ algorithm performed better than ArcView in minimizing the area modified in the process of creating a depressionless surface, particularly in flatter topography; 3) Areas affected by removing depressions are predominantly adjacent to the stream network; 4) For every elevation cell changed, slopes are changed for two to three cells, on average; and 5) ArcView and TOPAZ derived flow networks closely matched the blue line streams.
A Complex, Linked Watershed-Reservoir Hydrology and Water Quality Model Application for the Occoquan Watershed, Virginia
Xu, Zhongyan (Virginia Tech, 2005-12-16)
The Occoquan Watershed is a 1515 square kilometer basin located in northern Virginia and contains two principal waterbodies: the Occoquan Reservoir and Lake Manassas. Both waterbodies are principal drinking water supplies for local residents and experience eutrophication and summer algae growth. They are continuously threatened by new development from the rapid expansion of the greater Washington D.C. region. The Occoquan model, consisting of six HSPF and two CE-QUAL-W2 submodels linked in a complex way, has been developed and applied to simulate hydrology and water quality activities in the two major reservoirs and the associated drainage areas. The studied water quality constituents include temperature, dissolved oxygen, ammonium nitrogen, oxidized nitrogen, orthophosphate phosphorus, and algae. The calibration of the linked model is for the years 1993-95, with a validation period of 1996-97. The results show that a successful calibration can be achieved using the linked approach, with moderate additional effort. The spatial and temporal distribution of hydrology processes, nutrient detachment and transport, stream temperature and dissolved oxygen were well reproduced by HSPF submodels. By using the outputs generated by HSPF submodels, the CE-QUAL-W2 submodels adequately captured the water budgets, hydrodynamics, temperature, temporal and spatial distribution of dissolved oxygen, ammonium nitrogen, oxidized nitrogen, orthophosphate phosphorus, and algae in Lake Manassas and Occoquan Reservoir. This demonstrates the validity of linking two types of state of the art water quality models: the watershed model HSPF and the reservoir model CE-QUAL-W2. One of the advantages of the linked model approach is to develop a direct cause and effect relationship between upstream activities and downstream water quality. Therefore, scenarios of various land use proposals, BMP implementation, and point source management can be incorporated into HSPF applications, so that the CE-QUAL-W2 submodels can use the boundary conditions corresponding with these scenarios to predict the water quality variations in the receiving waterbodies. In this research, two land use scenarios were developed. One represented the background condition assuming all the land covered by forest and the other represented the environmental stress posed by future commercial and residential expansion. The results confirm the increases of external nutrient loads due to urbanization and other human activities, which eventually lead to nutrient enrichment and enhanced algae growth in the receiving waterbodies. The increases of external nutrient loads depend on land use patterns and are not evenly spread across the watershed. The future development in the non urban areas will greatly increase the external nutrient production and BMPs should be implemented to reduce the potential environmental degradation. For the existing urban areas, the model results suggest a potential threshold of nutrient production despite future land development. The model results also demonstrate the catchment function of Lake Manassas in reducing nutrient transport downstream.
A comprehensive modeling approach for BMP impact assessment considering surface and ground water interaction
Cho, Jae-Pil (Virginia Tech, 2007-04-04)
The overall goal of this study was to develop a comprehensive tool for assessing the effectiveness of selected BMPs on both hydrology and water quality and to demonstrate the applicability of the system by considering 1) temporally and spatially changing land use management practice in an agricultural watershed and 2) interaction between surface and ground water over the entire system. A user interface and Dynamic Agricultural Non-point Source Assessment Tool (DANSAT) were developed to achieve this goal. DANSAT is the only distributed-parameter, physically-base, continuous-simulation, and multi-soil layer model for simulating impacts of agricultural BMPs on hydrology and water qulality in small agricultural watersheds. DANSAT was applied to QNB plot (18m Ã 27m) and two agricultural watersheds in Virginia, including Owl Run watershed (1140 ha) and QN2 in the Nomini Creek watershed (216 ha), to evaluate the model components and its performance in predicting runoff, sediment yield, and pesticide load. DANSAT performed well in predicting total runoff and temporal variations in surface runoff for both field-scale and watershed-scale applications. Total percent errors between the measured and predicted results were less than 10% except for one case (39.8% within a subwatershed of Owl Run watershed), while the daily Nash-Sutcliffe model efficiencies were greater than 0.5 in all applications. Predicted total sediment yields were within ±35% of observed values in all applications. However, the performance of DANSAT in predicting temporal trend and spatial distribution of sediment loads was acceptable only within Owl Run watershed, where high correlations between flow rates and sediment loads exist. The predicted total pesticide loads were within ±100% of observed values. DANSAT failed to simulate the temporal occurrence of pesticide loads with a 0.42 daily Nash-Sutcliffe efficiency value. The Dual-Simulation (DS) was developed within the linked ground water approach to resolve problems encountered due to the existence of different temporal scales between DANSAT and the existing ground water models such as MODFLOW and MT3D. The linked approach performed better in predicting the seasonal trend of total runoff compared to the integrated approach by showing an increase in monthly Nash-Sutcliffe efficiency value from 0.53 to 0.60. Surface and subsurface output variables were sensitive to the changes in spatially distributed soil parameters such as total porosity and field capacity. A maximum grid size of 100 m was recommended to be appropriate for representing spatial distribution of topographic, land use, and soil characteristics based on accuracy analysis during the GIS manipulation processes. Larger time-step based on predefined acceptable maximum grid size, decreased the computational time dramatically. Overall sensitivity to different grid sizes and time-steps was smallest for hydrology components followed by sediment and pesticide components. Dynamic crop rotation was considered by DANSAT, and the model successfully simulated the impacts of temporal and spatial changes in crop rotations on hydrology and water quality for both surface and subsurface areas. DANSAT could prove to be a useful tool for non-point source pollution managers to assess the relative effectiveness of temporally and spatially changing BMPs on both surface and ground water quantity and quality.
A computer simulation model for investigating the effect of land application of sludge on runoff water quality
Deizman, Marcia McCutchan (Virginia Tech, 1989-04-22)
CREAMS-NT, a modified version of the field-scale model for Chemicals, Runoff, and Erosion from Agricultural Management Systems (CREAMS) model, was developed to simulate the nitrogen (N) transformations and subsequent nutrient transport processes which occur in the soil following organic waste applications. CREAMS-NT accounts for nutrient addition through fertilization and rainfall and losses of N by volatilization, denitrification, plant uptake, leaching, and overland flow. Data required by CREAMS-NT includes runoff volume, sediment yield, percolation, and soil environmental conditions which is generated by the hydrologic and erosion components of the original CREAMS model. The mineralization, nitrification, denitrification, ar1d volatilization processes are simulated using firstâ order knetic equations adjusted for the effects of soil environmental conditions including temperature, moisture, pH, soil/sludge contact, and soil cation exchange capacity. Prior to a runoff event, soil ammnonium-N (NH4 â N) is partitioned between adsorbed and desorbed phases. CREAMS-NT predicts the transport of organic-N, NH4 â N, and sediment=bound phosphorus (P3b) in runoff using enrichment ratios. The transport of soluble nutrients, nitrate-N (NO3 â N), NH4 â N, and soluble P (PTF), is estimated using extraction coefficients.
A computer simulation model for predicting pesticide losses from agricultural lands
Kenimer, Ann Lee (Virginia Tech, 1987-08-05)
A field scale model for predicting the surface losses of pesticides (Pesticide Losses In Erosion and Runoff Simulator, PLIERS) was developed. PLIERS accounts for pesticide losses by degradation and volatilization, the washoff of pesticides from plant canopy and surface residue, the adsorption and desorption of pesticides to and from soil particles, and the movement of pesticides in the dissolved and adsorbed phases. Hydrologic data are generated by the comprehensive watershed model, FESHM; which contains an extended sediment detachment and transport algorithm. PLIERS uses first order rate equations to describe degradation and volatilization, and pesticide washoff. The adsorption of pesticides to individual particle size classes is estimated using the Freundlich equation. Movement of atrazine and 2,4-D in runoff and sediment was measured on twelve field plots under simulated rainfall. The plots were treated with conventional or no-tillage in combination with one of three residue levels (0, 750, and 1500 kg/ha). Runoff and sediment losses were found to increase with decreasing residue cover for both tillage systems. No-till reduced sediment loss and total runoff volume by 98 and 92 percent, respectively, compared to conventional tillage. Concentrations of atrazine and 2,4-D ir1 runoff and sediment were greater from the no-till plots than from the conventional plots but the total losses were less. Both pesticides were carried predominately in the dissolved phase. Averaged over all plots, the atrazine losses were 2.9 percent of applied amount for conventional tillage and 0.3 percent for no-tillage. The corresponding values for 2,4-D were 0.3 percent and 0.02 percent. PLIERS was validated using data from the rainfall simulator field plot studies. Agreement between predicted and observed data was very good for dissolved pesticide losses and satisfactory for adsorbed pesticide losses. In addition, the effects of tillage type and residue level were reflected in PLIERS predictions. PLIERS shows great potential as a flexible planning tool since it could be used with any comprehensive hydrologic model and is able to predict the losses of pesticides under various field conditions.
Conservation agriculture and ecosystem services
Dillaha, Theo A. III (Blacksburg, VA: Virginia Tech, Office of International Research, Education, and Development (OIRED), 2009)
Conservation agriculture and ecosystem services
Dillaha, Theo A. III; Heatwole Shenk, Cheryl B.; Moore, Keith M. (American Society of Agricultural and Biological Engineers, 2010)
Conservation agriculture has many agricultural and food security benefits. In addition, conservation agriculture has potential on- and off-site ecosystem service benefits that are the focus of this paper. Ecosystem services provided by conservation agriculture fall into three main categories: provisioning services such as increased food production; regulating services such as carbon sequestration and climate regulation, reducing losses of soil, pesticides, nutrients and other potential contaminants in surface and subsurface water flows, and water cycle improvements; and supporting services such as nutrient and storage and cycling. This paper focuses on the regulating service benefits of conservation agriculture: erosion control, reduced losses of pesticides and nutrients, and particularly water cycle benefits including increased water productivity (more crop per drop), infiltration, percolation, plant available water storage, groundwater recharge, plant available water, and stream baseflow and decreases in peak stream flows and downstream flooding.
Denitrification in low pressure distribution onsite wastewater disposal systems
Degen, Marcia J. (Virginia Tech, 1992-12-05)
The effects of effluent type, effluent loading rate, dosing interval, and temperature on denitrification in low pressure distribution, on-site wastewater treatment and disposal systems (OSWTDS) were evaluated in this study. The treatments were surface and subsurface soil horizons; nitrified and non-nitrified wastewaters; 0.5, 1.0, and 1.5 times the Virginia Department of Health (VDH 1989) recommended wastewater loading rate; 24 and 48 hour dosing intervals; and summer and winter temperatures. Surface and subsurface soil cores were collected from a Groseclose silt loam soil (clayey, mixed, mesic Typic Hapludult) and subjected to the various treatments. The effects of the treatments on denitrification were evaluated based on analyses of leachate from the cores, soil chemical analyses, and microcosm studies to estimate actual denitrification activity. A model was developed from the study that estimated the mean N₂O production for each combination of experimental treatments. The results of the study and the model indicate that denitrification can be enhanced in OSWTDS by the application of non-nitrified wastewater at one-half the VDH recommended loading rate, or 1.25 cm/day, for surface soil horizons (30 min inch⁻¹ percolation rate) using a 48 hour dosing interval. A field study was conducted on a Lowell silt loam soil (fine, mixed, mesic Typic Hapludalf). Denitrification was measured at this site using acetylene blocking and the results compared to those predicted by the denitrification model developed from the laboratory data. The field measurements of denitrification based on N₂O concentration in the soil atmosphere were three orders of magnitude higher than that predicted by the model. It was concluded that the laboratory techniques can be used to determine optimum method of operation for denitrification in a low pressure distribution system, but it cannot be used to determine the field design loading rates.
Developing an adaptive management approach for small holder innovation
Moore, Keith M.; Dillaha, Theo A. III (SANREM CRSP, OIRED, Virginia Tech, 2006)
The objective of this presentation is to promote the development of a book to help development agents in developing (and developed) countries to better understand what is involved in the management of complex adaptive systems. The problem relates to linked rural poverty and environmental sustainability, though this can be solved through adaptive management for small holder innovation by providing development agents with knowledge and understanding to assist small holder innovation for adaptive management of complex adaptive systems (CAS). The objective is to encourage policy makers and donors to support local innovation and adaptive management.
Development of a continuous, physically-based distributed parameter, nonpoint source model
Bouraoui, Faycal (Virginia Tech, 1994-04-18)
ANSWERS, an event-oriented, distributed parameter nonpoint source pollution model for simulating runoff and sediment transport was modified to develop a continuous nonpoint source model to simulate runoff, erosion, transport of dissolved and sediment-bound nutrients, and nutrient transformations. The model was developed for use by nonpoint source pollution managers to study the long-tenn effectiveness of best management practices (BMPs) in reducing runoff, sediment, and nutrient losses from agricultural watersheds. The Holtan's infiltration equation used in the original version of ANSWERS was replaced by the physically-based Green-Ampt infiltration equation. Soil evaporation and plant transpiration were modeled separately using the Ritchie equation. If soil moisture exceeds field capacity, the model computes percolation based on the degree of soil saturation. Nutrient losses include nitrate, sediment-bound and dissolved ammonium; sediment-bound TKN, and sediment-bound and dissolved phosphorus. A linear equilibrium is assumed between dissolved and sediment-bound phases of ammonium and phosphorus. Nutrient loss is assumed to occur only from the upper cm of the soil profile. The model simulates transformations and interactions between four nitrogen pools including stable organic N, active organic N, nitrate and ammonium. Transformations of nitrogen include mineralization simulated as a combination of ammonification and nitrification, denitrification, and plant uptake of ammonium and nitrate. The model maintains a dynamic equilibrium between stable and active organic N pools.
Development of field-specific spring N rate recommendations for winter wheat
Scharf, Peter C. (Virginia Tech, 1993)
Optimum spring N fertilizer rates for winter wheat in Virginia vary widely from field to field, but traditionally spring N is applied at a uniform rate to all fields. A recently-developed tissue test procedure provides a field-specific evaluation of crop N status and predicts optimum N rate for the second spring N application in a split spring application management system. However, this procedure is based on a small number of researcher-planted experiments utilizing a single cultivar; it fails to provide field-specific rate recommendations for the first spring N application; and it is not accessible to farmers who are unwilling to split their spring N applications. Our objectives were: to evaluate the reliability of the tissue test procedure in a large number of farmer fields; to develop a method for making field-specific N rate recommendations for the first spring application in a split-application management system; and to develop a method for making field-specific N rate recommendations in a single-application management system. Forty-five spring N rate experiments were established in farmer fields over a five-year period. A range of N fertilizer rates was applied in early spring (Zadoks growth stage 25) and again in mid-spring (Zadoks growth stage 30) in all possible combinations. Yield data were used to calculate economic optimum N rates at growth stage (GS) 25 and GS 30 with split-application management, and at GS 25 with single-application management. These optima were regressed against a variety of predictor variables measured in the same fields. The reliability of the previously-developed tissue test procedure for making GS 30 N rate recommendations was confirmed. Tiller density was the best predictor of optimum GS 25 N rate with split-application management, while soil nitrate to 90 cm was the best predictor of optimum GS 25 N rate with single-application management. These three relationships fit together to form a flexible and powerful system for making spring N rate recommendations for winter wheat. This system increased estimated profit and apparent fertilizer efficiency in these experiments.

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