Browsing by Author "Wolfe, Mary Leigh"

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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.
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    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.
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    Analyzing Cost Implications of Water Quality Trading Provisions: Lessons from the Virginia Nutrient Credit Exchange Act
    Aultman, Stephen (Virginia Tech, 2007-07-26)
    The purpose of this study was to analyze the cost implications of various provisions of the Virginia Nutrient Credit Exchange Act. The first objective was to estimate the cost implications of point source trading provisions of the Act. An integer programming cost minimization model was constructed to estimate the cost of achieving four point source trading policy scenarios. The model estimated the annual cost of meeting two different nutrient cap levels, each with and without a limits-of-technology concentration standard requirement for new and expanding point sources. The limits-of-technology concentration standard requirement was found to significantly affect cost while providing little apparent benefit to water quality. The second objective was to develop a screening procedure for municipalities to estimate the cost of generating waste load allocation from nonpoint source offsets under their jurisdictional control. A spreadsheet based cost screening procedure was developed for municipalities to estimate the cost of implementing of nitrogen offsets from stormwater practices, septic retirement, and land conversion. One of the important findings from developing the screening procedure is that the cost of generating WLA from non-point sources under the control of local governments was much higher than the cost of removing nitrogen at wastewater treatment plants.
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    Applying Probabilistic Risk Assessment to Agricultural Nonpoint Source Pollution
    Buck, Sharon Perkins (Virginia Tech, 1997-01-30)
    A probabilistic risk assessment (PRA) for the discharge of excessive nitrogen from nonpoint sources (NPSs) to a stream was performed for a small agricultural watershed in northern Virginia. Risk, by definition, is the product of the frequency of occurrence of an event and the consequences of that event. The purpose of this research was to determine the probability of occurrence of a nitrogen discharge event (i.e., frequency). The consequences of such a discharge event were not explicitly determined but were implicitly assumed to be negative in nature. An event tree was developed to show the basic hydrologic processes at work in a small watershed. However, the event tree could not be used to discover the causes for nitrogen loss from the watershed. Therefore, a fault tree was developed for excessive nitrogen discharge in surface runoff on any day from agricultural sources. The development of the fault tree was found to be a useful exercise in understanding the intricate cause and effect relationships between agricultural practices and NPS pollution. Based on the results, the fault tree methodology might be used as an effective teaching or communication tool. The fault tree was also evaluated quantitatively to determine a probability of occurrence for excessive nitrogen discharge to the stream on any day. Land use, fertilization, monitoring, and long-term weather records were used in conjunction with scientific judgment and expert opinion to establish the probabilities within the fault tree and to calculate the overall probability of nitrogen discharge to the stream on any day. The results obtained from the fault tree calculations tend to underestimate the importance of cropland best management practices (BMPs) over the long term, because the fault tree was developed on a daily basis (i.e., every day in a year has the same probability of a discharge event occurring). A more accurate depiction of the NPS pollution control problem was achieved by assuming the occurrence of a runoff event. A second fault tree was presented for the discharge of excessive nitrogen to the stream during a runoff event. The quantitative assessment of the new fault tree showed more clearly the impact of BMPs on reducing the likelihood of nitrogen discharge. A 0.15 decrease in the probability of nitrogen discharge during a runoff event was calculated for the Owl Run watershed from 1987 to 1993 due to the effects of BMPs installed during that time period. A 0.20 decrease was calculated for an Owl Run subwatershed for the same time period. This subwatershed isolated two major dairy operations and the effects of the BMPs installed for those dairies. Despite the success of the fault tree in mirroring changes within the watershed, the amount of data and time required to perform the quantitative assessment may limit its use in the NPS pollution control field. The basic nature of the fault tree technique also limits its usefulness in the field. One such limitation is that degrees of events cannot be expressed. For example, a BMP is either present or not present on a fault tree. There can be no indication of how effective the BMP is in preventing NPS pollution without substantially increasing the level of detail displayed by the tree. Another limitation is that the ultimate result of the fault tree calculations is a probability of occurrence. This value is not as easily understood as the output of NPS pollution computer models, for example, where the output has specific meaning and units (e.g., milligrams of nitrogen per liter of runoff). The qualitative fault tree, however, has the advantage over computer models when it comes to understanding the concepts behind the technique and being able to see the cause and effect relationships at work in the watershed. Laypersons can understand the fault tree more easily than the complex computer code and intricate equations of models.
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    Assessment of SWAT to Enable Development of Watershed Management Plans for Agricultural Dominated Systems under Data-Poor Conditions
    Osorio Leyton, Javier Mauricio (Virginia Tech, 2012-05-02)
    Modeling is an important tool in watershed management. In much of the world, data needed for modeling, both for model inputs and for model evaluation, are very limited or non-existent. The overall objective of this research was to enable development of watershed management plans for agricultural dominated systems under situations where data are scarce. First, uncertainty of the SWAT model's outputs due to input parameters, specifically soils and high resolution digital elevation models, which are likely to be lacking in data-poor environments, was quantified using Monte Carlo simulation. Two sources of soil parameter values (SSURGO and STATSGO) were investigated, as well as three levels of DEM resolution (10, 30, and 90 m). Uncertainty increased as the input data became coarser for individual soil parameters. The combination of SSURGO and the 30 m DEM proved to adequately balance the level of uncertainty and the quality of input datasets. Second, methods were developed to generate appropriate soils information and DEM resolution for data-poor environments. The soils map was generated based on lithology and slope class, while the soil attributes were generated by linking surface soil texture to soils characterized in the SWAT soils database. A 30 m resolution DEM was generated by resampling a 90 m DEM, the resolution that is readily available around the world, by direct projection using a cubic convolution method. The effect of the generated DEM and soils data on model predictions was evaluated in a data-rich environment. When all soil parameters were varied at the same time, predictions based on the derived soil map were comparable to the predictions based on the SSURGO map. Finally, the methodology was tested in a data-poor watershed in Bolivia. The proposed methodologies for generating input data showed how available knowledge can be employed to generate data for modeling purposes and give the opportunity to incorporate uncertainty in the decision making process in data-poor environments.
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    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.
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    BMP Cost and Nutrient Management Effectiveness on Typical Beef and Beef-Poultry Farms in Shenandoah County, Virginia
    Dickhans, Megan F. (Virginia Tech, 2010-05-04)
    This study analyzes the change in whole-farm net revenues and nutrient reduction from the implementation of five best management practices (BMPs) on a typical beef and beef-poultry farm in Shenandoah County. Whole-farm net revenues, resource allocation, nutrient loss reductions, and the cost efficiency of reducing nutrient losses were analyzed to assess which BMPs are the most cost efficient to implement, assuming the baseline scenarios have no voluntarily applied BMPs. The effects of stacking additional BMPs, in combinations of two or more, were also assessed. No-till cropping, winter wheat cover crop, herbaceous riparian buffer, fencing, and P-based NMP were the BMPs that were analyzed. Incentive payments from state and federal governments were incorporated into the cost of BMP adoption. A brief analysis of a farmer's time value of money, with respect to incentive payments, was also conducted. Results indicated that no-till crop management was the most cost efficient BMP, and was the only BMP to increase net revenues for both farm models. Fencing and P-based NMP were the least cost efficient for the beef farm. For the beef-poultry farm, fencing was the least cost efficient. The implications of this study are that farmers that choose to adopt BMP should evaluate both their interests in maintaining (or increasing) farm net revenues along with their interest in improving water quality through the reduction of nutrient losses. There is potential for implementing multiple BMPs, while increasing net revenues from a farm's baseline scenario. For farmers and policy makers, no-till cropping can be a profitable and therefore cost efficient BMP to implement. Incentive payments are intended to encourage the adoption of BMPs by subsidizing a portion of the start-up costs. Policy makers should attempt to make cost-share payments reflect nutrient reduction goals. This can be done by analyzing both the compliance cost to farmers and the nutrient reduction effectiveness of BMPs.
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    Collaborative Study and Paired Test Taking in Collegiate Level Linear Programming Instruction
    Angel, N. Faye (Virginia Tech, 1998-09-16)
    The purpose of this investigation was to examine the effects of collaborative learning strategies on formulating solutions to linear programming word problems that were designed to incorporate problem-solving skills. Forty-six students majoring in business at a small southwest college in Virginia participated in the study. After an instruction session, a study period, and a question and answer discussion, participants completed the test instrument based upon random assignment to three treatment groups. These included individual study with individual test taking (control), paired study with individual test taking, and paired study with paired test taking. All participants returned in 17 days to complete a posttest individually having received no further instruction in linear programming theory. The following null hypothesis was examined: No differences in treatment means measuring problem-solving abilities would be found based on students' test and posttest scores using two treatment groups of collaborative study, with collaborative or individual test taking, and a control group of individual study with individual test taking. After satisfying the assumptions of no difference in ability in the treatment groups, establishing significant influence of ability on test score and posttest score variables, and establishing homogeneity of regression, an analysis of covariance (ANCOVA) was used to test the null hypothesis. The null hypothesis was rejected. Treatment had a significant effect on the variance for the test score variable, F = 3.92, p < .05, and for the posttest score variable, F = 4.44, p < .05. Newman-Keuls post hoc test showed significant differences in the adjusted means of the test score variable between the individual study with individual test taking group (72.22) and the paired study with paired test taking group (87.86). For the posttest score variable, the Newman-Keuls post hoc test revealed significant differences between the adjusted means of the individual study with individual test taking group (36.25) and the paired study with individual test taking group (59.20), and between the adjusted means of the individual study with individual test taking group (36.25) and the paired study with paired test taking group (55.77). Implications of findings and recommendations for further research were discussed.
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    A Comparative Study of Stream-Gaging Methods Employed in Nonpoint Source Pollution Studies in Small Streams
    Mitchem, Charles E. Jr. (Virginia Tech, 1998-04-09)
    The U.S. Geological Survey started measuring stream flow in 1888 as part of a public land irrigation study. The demand for accurate stream flow measurement has increased with the rising concern about nonpoint source (NPS) pollution. NPS pollution studies, such as TMDL development, often involve quantification of flow in small first and second order streams. This application of technology intended for use in larger streams presents special problems that must be addressed by the user. The goal of this study was to conduct a comparative analysis of the current technologies used to measure flow in small streams with respect to accuracy and cost. The analyses involved field investigations, laboratory experiments, and a cost analysis. The specific study objectives were: 1) Compare the accuracy of various methods for estimating stream discharge in small first and second order streams, 2) Compare the accuracy of various methods for estimating stream discharge in a controlled laboratory environment, and 3) Evaluate the costs associated with installation, operation, and maintenance of each of the systems investigated. Ten stream-gaging methods were evaluated for their field performance, laboratory performance, and costs. Analysis of the field investigation data indicated that the Marsh McBirney current meter and the One-orange method were the most accurate among the methods studied. The results of the laboratory experiments imply that the Starflow acoustic Doppler and Valeport BFM001 current meter performed best among the ten methods. The Starflow acoustic Doppler device also proved to be the most cost-effective method. Overall, the Marsh McBirney and Valeport BFM001 current meters exhibited the best performance for both field and laboratory situations among the methods evaluated.
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    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.
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    Comparison of watershed boundaries derived from SRTM and ASTER digital elevation datasets and from a digitized topographic map
    Pryde, J. K.; Osorio, J.; Wolfe, Mary Leigh; Heatwole, Conrad D.; Benham, Brian L.; Cardenas, A. (2007)
    Watersheds are natural integrators of hydrological, biological, and geological processes and as such require an integrated approach to data analysis and modeling, which usually starts delineating accurately a polygon vector layer of watershed boundaries as input. In that way, the Río Illangama watershed in Alto Guanujo, Ecuador, had been isolated with the objective of evaluate the accuracy of watershed boundaries derived from three different sources: One was delineated by hand and the other two were derived from a 30-m ASTER DEM and a 90-m SRTM DEM, using the Spatial Analyst extension of ArcGIS. Visually, there are small differences between the manually-delineated and the SRTM-based boundaries, while the ASTER-based varies from the manually-delineated one. The area of the watershed delineated manually is 13,061.3 ha, while the SRTM-based and the ASTER-based watershed are 0.66% and 2.6% larger. The regression analyses comparing the complete boundaries yielded an R2 of 0.999 between the SRTM and manual boundaries and the 0.988 for the ASTER and the manual boundaries. The t-test comparing DEMs indicated a significant difference (p
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    Constructed Floodplain Wetland Effectiveness for Stormwater Management
    Ludwig, Andrea L. (Virginia Tech, 2010-07-20)
    A 0.2-hectare wetland was constructed in the floodplain of Opequon Creek in Northern Virginia as a best management practice (BMP) for stormwater management. The research goals were to 1) determine if wetland hydrology existed and quantify the role of groundwater exchange in the constructed wetland (CW) water budget, 2) estimate wetland hydraulic characteristics during overbank flows, and 3) quantify the event-scale nutrient assimilative capacity of the constructed wetland. CW water table elevations and hydraulic gradients were measured through an array of nested piezometers. During controlled flooding events, stream water was pumped from the creek and amended with nutrients and a conservative tracer in two seasons to determine hydraulic characteristics and nutrient reduction. Samples were collected at the inlet, outlet structure, and at three locations along three transects along the wetland flowpath. Water table elevation monitoring demonstrated that wetland hydrology existed on the site. The mean residence time of the wetland was found to be 100 min for flow-rates of 4.25-5.1 m3/min. Residence time distributions of the high and low marsh features identified a considerable degree of flow dispersion. Manning's n varied between macrotopographic features and was significantly higher in the spring event as compared to the fall event, likely due to the presence of rigid-stem vegetation. Average wetland n was 0.62. Total suspended solid concentrations decreased with increasing residence time during both experiments. Mass reduction of pollutants were 73% total suspended solids (TSS), 54% ammonia-nitrogen (NH3-N), 16% nitrate-N (NO3-N), 16% total nitrogen (TN), 23% orthophosphate-phosphorus (PO4-P), and 37% total P (TP) in the fall, and 69% TSS, 58% NH3-N, 7% NO3-N, 22% TN, 8% PO4-P, and 25% TP in the spring. Linear regression of mass flux over the event hydrograph was used to determine pollutant removal rates between the wetland inlet and outlet. Pollutant removal rates were determined through linear regression of mass flux and were higher in the spring event than in the fall. Dissolved nitrogen species were more rapidly removed than dissolved phosphorus. TSS, TP, and TN removal were greater and faster than dissolved nutrient species, suggesting that physical settling was the dominant removal mechanism for stormwater pollutants.
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    Cost-effective BMP placement: Optimization versus targeting
    Veith, Tamie L.; Wolfe, Mary Leigh; Heatwole, Conrad D. (American Society of Agricultural and Biological Engineers, 2004)
    Cost-effectiveness of nonpoint-source pollution reduction programs in an agricultural watershed depends on the selection and placement of control measures within the watershed. Locations for best management practices (BMPs) are commonly identified through targeting strategies that define locations for BMP implementation based on specific criteria uniformly applied across the watershed. The goal of this research was to determine if cost-effectiveness of BMP scenarios could be improved through optimization rather than targeting. The optimization procedure uses a genetic algorithm (GA) to search for the combination of site-specific practices that meets pollution reduction requirements, and then continues searching for the BMP combination that minimizes cost. Population size, replacement level, crossover, and mutation parameters for the GA were varied to determine the most efficient combination of values. A baseline scenario, a targeting strategy, and three optimization plans were applied to a 1014 ha agricultural watershed in Virginia. All three optimization plans identified BMP placement scenarios having lower cost than the targeting strategy solution for equivalent sediment reduction. The targeting strategy reduced average annual sediment loss compared to the baseline at a cost of $42 per kg sediment reduction/ha. The optimization plan with the same BMP choices achieved the same sediment reduction at a cost of $36 per kg/ha. Allocation of BMPs varied among optimization solutions, a possibility not available to the targeting strategy. In particular the optimization solutions placed BMPs on several stream-edge fields that did not receive BMPs in the targeting strategy.
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    Cover crop/dairy manure management systems: Water quality and soil system impacts
    Kern, James D.; Wolfe, Mary Leigh (American Society of Agricultural and Biological Engineers, 2005)
    A field study was conducted to determine impacts of corn silage production systems that included a rye cover crop and application of liquid dairy manure in the spring and fall on water quality and soil characteristics. Four management systems were each replicated four times: traditional, double-crop, roll-down, and undercut. Manure was applied below the soil surface during the undercutting process; otherwise, manure was surface applied. In the roll-down system, the rye crop was fattened with a heavy roller after manure application. Rainfall was simulated within 48 h of manure application to produce runoff events. Grab samples of runoff were collected and composited for analysis. Soil samples were collected prior to treatments in the fall and spring. The roll-down system had no significant effect on water quality (sediment, nutrients, bacteria) as compared to the traditional system. While the roll-down system may require an occasional tillage operation to prevent surface compaction, it is recommended in situations where reduction of residual herbicide applications is a primary concern. The undercut system displayed evidence of a compaction layer developing below the disturbed soil layer. The undercut system reduced loadings of all nutrients, but increased losses of total suspended solids, as compared with all other systems. Mean volume of runoff from the undercut system was less than half that from any other system. Overall, the undercut system is recommended over the other systems analyzed for preventing transport of manure constituents to surface water, but should be evaluated in a complete dairy system before it is implemented by producers.
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    Development and Comparison of 17beta-Estradiol Sorption Isotherms for Three Agriculturally Productive Soils From Different Physiographic Regions in Virginia
    Kozarek, Jessica Lindberg (Virginia Tech, 2005-08-10)
    Natural steroid estrogens such as 17beta-estradiol in low nanogram per liter concentrations can adversely affect the reproductive health of aquatic organisms. The overall goal of this research was to quantify the sorption of 17beta-estradiol to three soils considered to be agriculturally productive from different physiographic regions in Virginia to aid in modeling the concentration of estrogens available for transport in runoff from agricultural fields. Batch equilibrium experiments were conducted with various concentrations of 17beta-estradiol (E2) in a background solution of 5 mM calcium chloride and 100 mg/L sodium azide added to four separate soil samples representative of productive agricultural soils from three different physiographic regions of Virginia. Groseclose loam, Myatt sandy loam and Cecil loam were supplied by the Crop and Soil Environmental Sciences Department at Virginia Tech. All soils were collected from the plow layer (0 to 15 cm) except for an additional Cecil soil sample from the Bt horizon. The concentration of E2 in the liquid phase was measured by gas chromatography/mass spectrometry (GC/MS) and was used to find the time to reach equilibrium and to develop sorption isotherms for each soil. The time required to reach equilibrium for all soils was less than 24 hours. A linear isotherm provided the best fit to model the sorption of E2 to Cecil and Myatt soils (R2 = 0.94 and 0.96, respectively). For Groseclose soil, the general form of the Freundlich isotherm fit best (R2 = 0.98), although the linear isotherm also provided a good fit (R2 = 0.93). The sorption of E2 to agricultural soil appears to be related to the organic carbon content of each soil (Pearson coefficient, 0.82). Attempts to analyze and create isotherms for conjugated E2 by deconjugating with metholysis were unsuccessful.
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    Effects of Spatial Information on Estimated Farm Nonpoint Source Pollution Control Costs
    Bonham, John G. (Virginia Tech, 2003-07-02)
    In the state of Virginia, population growth and the associated increases in municipal wastewater, along with the threat of EPA regulations, will increase the need for reductions in phosphorous (P) loads in surface waters in order to meet and maintain water quality standards for the Chesapeake Bay. Agriculture contributes 49% of P entering the Bay; therefore, it can be expected that agriculture will be targeted as a source of P reductions. Spatially variable physical and socioeconomic characteristics of a watershed and its occupant farms affect both the decisions made by farmers and the transport of nutrients. Evidence suggests that spatially variable characteristics should be considered when designing policies to control nonpoint sources of water pollution. However, spatial information can be expensive to collect and the evidence is not conclusive as to the level of information required to analyze specific pollution-control policies. The objective of this study was to estimate the accuracy of predicted compliance costs and changes in P deliveries resulting from mandatory buffer installation and mandatory nutrient management for three alternative levels of information, relative to the population of farms in a Virginia watershed. For each information case, an economic model, FARMPLAN, was used to determine the profit maximizing levels of inputs, outputs and gross margins. Selected crop rotations and P applications were used as inputs to the physical model, PDM, which estimated the levels of P delivered to the watershed outlet. The compliance cost and P reduction estimates for the three alternative cases were compared to those of the population to determine their accuracy. The inclusion of greater levels of spatial information will lead to more accurate estimates of compliance costs and pollution reductions. Estimates of livestock capacity are more important to making accurate predictions than are farm boundaries. Differences in estimates made using different levels of information will be greater when the farmers have greater flexibility in meeting the policy requirements. The implications are that additional spatial information does not aid in the selection of one policy over the other, but can be useful in when estimating costs for budgeting purposes, or when evaluating how farmers will respond to the policy.
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    Enhanced Biological Phosphorus Removal from Dairy Manure to Meet Nitrogen:Phosphorus Crop Nutrient Requirements
    Yanosek, Kristina Anne (Virginia Tech, 2002-10-18)
    Over the last two decades, livestock operations have become highly concentrated due to growing trends towards larger, more confined facilities and a decrease in cropland on smaller farms. This has led to greater amounts of excess manure nutrients on farms, increasing the potential for nutrient pollution of water bodies from runoff. The purpose of this study was to determine if enhanced biological phosphorus removal (EBPR) is a viable alternative for managing excess manure nutrients on dairy farms. Assessment of EBPR involved the investigation of various aspects of wastewater treatment modeling and design and farm nutrient management. The fermentation potential (volatile fatty acid (VFA) production) of dairy manure was determined through laboratory analysis to be 15.3% of the total COD. Total VFA production was composed of 57, 23, and 20% acetic, propionic, and butyric acids, respectively. The EBPR component of the BioWin wastewater treatment model was evaluated through a sensitivity analysis. The parameters to which effluent phosphate (PO4) concentration was most sensitive were maximum specific growth rate, growth yield, aerobic PO4 uptake rate per unit poly-b-hydroxybutyrate (PHB) utilized, PHB yield from VFA, PO4 release per unit VFA uptake, and fraction of releasable PO4. An EBPR sequencing batch reactor (SBR) was designed for a dairy farm with 700 lactating cows and 325 ha of corn silage. An economic analysis of EBPR for dairy farms employing P-based manure applications was completed. The cost of hauling excess manure to nutrient deficient farms was the most significant expense in comparing costs of manure management with and without EBPR. For a herd of 700 lactating cows, utilizing EBPR was more economical for farms with 270 ha or less cropland, while EBPR did not offer an economic advantage for farms over 270 ha.
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    Estimating Bacterial Loadings to Surface Waters from Agricultural Watersheds
    Panhorst, Kimberly A. (Virginia Tech, 2002-12-13)
    Fecal bacteria and pathogens are a major source of surface water impairment. In Virginia alone, approximately 73% of impaired waters are impaired due to fecal coliforms (FC). Because bacteria are a significant cause of water body impairment and existing bacterial models are predominantly based upon laboratory-derived information, bacterial models are needed that describe bacterial die-off and transport processes under field conditions. Before these bacterial models can be developed, more field-derived information is needed regarding bacterial survival and transport. The objectives of this research were to evaluate bacterial survival under field conditions and to develop a comprehensive, spatially variable (distributed) bacterial model that requires little or no calibration. Three field studies were conducted to determine die-off or diminution (settling plus die-off) rates of FC and Escherichia coli (EC) over time in: 1) dairy manure storage ponds and turkey litter storage sheds, 2) pasture and cropland soils to which dairy manure was applied, and 3) beef and dairy fecal deposits. The dairy manure storage ponds were sampled just under the pond surface. The FC and EC diminution (settling plus die-off) rates for dairy manure storage ponds were 0.00478 day⁻¹ and 0.00781 day⁻¹, respectively. The five samples collected for turkey litter in storage were inadequate to draw any conclusions. Bacterial die-off rates in cropland and pastureland soils were found to be statistically different from each other at the α = 0.05 level. The FC and EC die-off rates in cropland soils were 0.01351 day⁻¹ and 0.01734 day⁻¹, respectively, while the FC and EC die-off rates in pastureland soils were 0.02246 day⁻¹ and 0.02796 day⁻¹, respectively. Die-off rates for bacteria from dairy heifer, dairy milker, and beef cow fecal deposits were not statistically different from each other. The resulting die-off rate constants for fecal deposits were 0.01365 day⁻¹ and 0.01985 day⁻¹ for FC and EC, respectively. The EC/FC ratio was also evaluated for the fecal deposits and land-applied manure to determine if a quantifiable relationship was discernable. In general the EC/FC ratio declined over time, but no quantifiable relationship was discerned. The bacterial model simulates die-off, bacterial partitioning between soil and water, and bacterial transport to surface waters in free (in solution) and sediment-adsorbed forms. Bacterial die-off was modeled using Chick's Law, bacterial partitioning was modeled with a linear isotherm equation, and bacterial transport was modeled using continuity and flow equations. The bacterial model was incorporated into the ANSWERS-2000 model, a continuous, distributed, nonpoint source pollution model. The model was tested using data from two plot studies. Calibration was required to improve runoff and sediment predictions. Bacterial model predictions underpredicted bacterial concentrations in runoff with a maximum underprediction error of 92.9%, but predictions were within an order of magnitude in all cases. Further model evaluation, on a larger watershed with predominantly overland flow, over a longer time period, is recommended, but such data were not available at the time of this assessment. The overall conclusions of this research were 1) FC and EC die-off or diminution under the examined field conditions followed Chick's Law, 2) measured die-off rate constants in the field were much less than those cited in literature for laboratory experiments, and 3) for the conditions simulated for two plot studies, the bacterial model predicted bacterial concentrations in runoff within an order of magnitude.
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    Estimating Exposure and Uncertainty for Volatile Contaminants in Drinking Water
    Sankaran, Karpagam (Virginia Tech, 1998-09-05)
    The EPA recently completed a major study to evaluate exposure and risk associated with a primary contaminant, radon and its progeny in drinking water (EPA, 1995). This work resulted in the development of a Monte Carlo Simulation model written in the programming language C. The model developed by the EPA has been used to estimate the cancer fatality risk from radon in water for exposed populations served by community ground water supplies, and to provide a quantitative analysis of the uncertainty associated with the calculations (EPA, 1995). This research is a continuation of the study conducted by the EPA. In this project, a Monte Carlo computer model will be developed to evaluate the risk associated with exposure to volatile compounds in drinking water. The model will be based on a computer program (developed previously by the EPA) for estimating the risks associated with exposure to radon in drinking water. The model will be re-implemented in the form of a computer program written in C. The analysis for radon will be extended to include the entire range of contaminants found in drinking water supplies. The initial focus of the project has been on extending the analysis to cover the ingestion exposure pathway for volatile compounds, but ultimately the risk via ingestion and dermal sorption will also be evaluated. The integrated model can estimate the risks associated with various levels of contaminants in drinking water and should prove valuable in establishing Maximum Contaminant Levels (MCLs) for the entire range of contaminants found in water supplies and generated in water treatment and distribution systems.
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    Estimating Soil Nitrogen Supply and Fertilizer Needs for Short-Rotation Woody Crops
    Scott, David Andrew (Virginia Tech, 2002-10-25)
    Short-rotation woody crops are becoming important supplies of hardwood fiber, but little is known about the early nutritional needs of these systems, especially on different site types. The study objectives were, on two young (ages 3-6) sweetgum plantations with contrasting soil types, to 1) determine the plant growth and foliar nutrition response to repeated nitrogen (N) fertilizer applications, 2) determine soil N supply, plant N demand, foliar N resorption, and soil and fertilizer uptake efficiencies, and 3) test a simple N supply model. In order to expand the findings to the range of sweetgum site types, the study objectives were also to 4) evaluate rapid methods for determining N mineralization potential, 5) characterize the soils of 14 sweetgum site types in the Atlantic coastal plain, and 6) review current N fertilizer prescriptions in forestry and recommend strategies for improvement. Two young sweetgum (Liquidambar styraciflua L.) plantations on a converted agricultural field and a pine cutover site in South Carolina were fertilized biannually with three rates of N fertilizer (0, 56, 112 kg N per ha). Fertilization doubled foliar biomass and leaf area on the cutover pine site in the years fertilizer was applied, and stem biomass increased 60%. Critical values, the N concentration required for 90% of optimum growth, is approximately 1.75%. Foliar N uptake increased at both sites when fertilizer was applied. Modeled annual soil N supply was within 20% of that measured on the two plantations even though monthly N supply was not accurately estimated. Potential N mineralization was accurately estimated with a 3-day incubation of rewetted soils that were previously dried, but not by hot salt extraction or anaerobic incubation. Across a spectrum of 14 sweetgum sites, the agricultural fields had lower mineralizable nitrogen (126 kg per ha) than the cutover sites (363 kg per ha). Current N fertilizer prescriptions are not sufficient for repeated fertilizer applications to fast-growing hardwood plantations, but simple models of soil N supply and an N-balance approach may improve prescriptions.