Models to estimate hydraulic resistance due to vegetation in emergent wetlands are crucial to wetland design and management. Hydraulic models that consider vegetation rely on an accurate determination of a resistance parameter such as a friction factor or a bulk drag coefficient. At low Reynolds numbers typical of flows in wetlands, hydraulic resistance is orders of magnitude higher than fully turbulent flows and resistance parameters are functions of the flow regime as well as the vegetation density and structure. The exact relationship between hydraulic resistance, flow regime and vegetation properties at low-Reynolds number flows is unclear. The project goal was to improve modeling of emergent wetlands by linking vegetation and flow properties to hydraulic resistance. A 12.2-m x 1.2 m vegetated flume was constructed to evaluate seven models of vegetated hydraulic resistance through woolgrass (Scirpus cyperinus (L.) Kunth), a common native emergent wetland plant. Measurements of vegetation geometry and structure were collected after each set of flume runs. Study results showed at low stem-Reynolds numbers (<100), the drag coefficient is inversely proportional to the Reynolds number and can vary greatly with flow conditions. Empirical models that were developed from data collected in natural wetlands predicted flow velocity most accurately. Using data from this flume study, regression models were developed to predict hydraulic resistance. Results indicated stem Reynolds number, stem diameter, and vegetation area per unit volume were the best predictors of friction factor. Vegetation flexibility and water depth were also important parameters but to a lesser extent. The spatial distribution of hydraulic resistance was estimated in a small floodplain wetland near Stephens City, VA using the regression models developed from the flume data. MODFLOW was used to simulate a 4-hour flood event through the wetland. The vegetated open water surface was modeled as a highly conductive aquifer layer. On average, MODFLOW slightly underpredicted the water surface elevation. However, the model error was within the range of survey error. MODFLOW was not highly sensitive to small changes in the estimated surface hydraulic conductivity caused by small changes in vegetation properties, but large decreases in surface hydraulic conductivity dramatically raised the elevation of the water surface. / Ph. D.

A petroleum-contaminated soil remediation study was conducted in a greenhouse. The system consisted of 36 pots, 12 were vegetated with squash, 12 were vegetated with fescue grass and the last 12 units served as unvegetated controls. For each group, three treatments were applied, 1) the addition of single dose of nutrients, 2) the addition of double dose of nutrients and 3) the addition of double dose of nutrients and acclimated bacteria to the irrigation water. The two plants were selected to represent extremely different species in terms of transpiration potential and root density in order to better understand the mechanisms involved in phytoremediation. Clay sandy soil (3: 1, by weight) was spiked with Fuel oil No.2 and allowed to weather for 1 week before it was placed in the pots. Under all study treatments, units vegetated with fescue grass had significantly less TPH concentration than the unvegetated controls after 10 weeks. Units vegetated with squash had significantly less TPH concentration than the un vegetated controls after 10 weeks only under treatment 3. Squash significantly accumulated TPH in the shoot under all treatments while grass shoot accumulated TPH significantly only under treatment 1. The mechanisms most important in phytoremediation seemed to include plant uptake of TPH, desorption and enhanced bioavailability by transpiration-induced water movement in the rhizosphere and root stimulation of microbial degradation. / Ph. D.

Data from an airborne laser scanner, a dual-band interferometric synthetic aperture radar (DBInSAR), and Landsat were evaluated for estimating ages of even-aged loblolly pine stands in Appomattox-Buckingham State Forest, Virginia, U.S.A. The DBInSAR data were acquired using the GeoSAR sensor in summer, 2008 in both the P- and X-bands. The LiDAR data were acquired in the same summer using a small-footprint laser scanner. Loblolly pine stand ages were assigned using the establishment year of loblolly pine stands provided by the Virginia Department of Forestry. Random circular plots were established in stands which varied in age from 5 to 71 years and in site index from 21 to 29 meters (base age 25 years). LiDAR- and GeoSAR-derived independent variables were calculated. The final selected LiDAR model used common logarithm of age as the dependent variable and the 99.5th percentile of height above ground as the independent variable (R2adj = 90.2%, RMSE = 4.4 years, n=45). The final selected GeoSAR models used the reciprocal of age as the dependent variable and had three independent variables: the sum of the X-band magnitude, the 25th percentile of X/P-band magnitudes, and the 90th percentile of the X-band height above ground (R2adj = 84.1%, RMSE = 7.9 years, n=46). The Vegetation Change Tracker (VCT) algorithm was run using a digital elevation layer, a land cover map, and a series of Landsat (5 and 7) images. A comparison was made between the loblolly pine stand ages obtained using the three methods and the reference data. The results show that: (1) although most of the time VCT and reference data ages were different, the differences were normally small, (2) all three remote sensing methods produced reliable age estimates, and (3) the Landsat-VCT algorithm produced the best estimates for younger stands (5 to 22 years old, RMSEVCT=2.2 years, RMSEGeoSAR=2.6 years, RMSELiDAR=2.6 years, n=35) and the model that used LiDAR-derived variables was better for older stands. Remote sensing can be used to estimate loblolly pine stand age, though prior knowledge of site index is required for active sensors that rely primarily on the relationship between age and height. / Ph. D.

Yes / The present study investigates the turbulent hydrodynamics in an open channel flow with an emergent and sparse vegetation patch placed in the middle of the channel. The dimensions of the rigid vegetation patch are 81 cm long and 24 cm wide and it is prepared by a 7× 10 array of uniform acrylic cylinders by maintaining 9 cm and 4 cm spacing between centers of two consecutive cylinders along streamwise and lateral directions respectively. From the leading edge of the patch, the observed nature of time averaged flow velocities along streamwise, lateral and vertical directions is not consistent up to half length of the patch; however the velocity profiles develop a uniform behavior after that length. In the interior of the patch, the magnitude of vertical normal stress is small in comparison to the magnitudes of streamwise and lateral normal stresses. The magnitude of Reynolds shear stress profiles decreases with increasing downstream length from the leading edge of the vegetation patch and the trend continues even in the wake region downstream of the trailing edge. The increased magnitude of turbulent kinetic energy profiles is noticed from leading edge up to a certain length inside the patch; however its value decreases with further increasing downstream distance. A new mathematical model is proposed to predict time averaged streamwise velocity inside the sparse vegetation patch and the proposed model shows good agreement with the experimental data. / Debasish Pal received financial assistance from SRIC Project of IIT Kharagpur (Project code: FVP)

This thesis is a result of a survey of elementary school principals at schools with grades kindergarten through 5th in Virginia to determine whether and how attitudes of principals influence vegetation levels on school grounds. The research also looked to find other contributing factors. Principals' educational backgrounds and age proved to be non-influencing factors. However, gender did influence school grounds with women being more likely to administer school grounds with fewer trees and tree plantings than men. Levels of tree vegetation and tree plantings proved to be highly influential in satisfaction with appearance of school grounds. Non-urban schools were more likely to have higher levels of vegetation than urban schools. Parental, service club, and local business involvement are linked together in respondents' satisfaction with each influencing the perception of the others. Analyses of these results can help groups target schools for grounds improvement projects. By understanding what effect principals have on their school grounds steps can be taken at the level of individual schools, school boards, and communities to help improve school grounds. / Master of Science

This investigation has for its aim the determination and the evaluation of the vegetational composition in certain farm pastures in Denton County, Texas.

Atmospheric dust is the largest contributor to global aerosols from land. Dust emissions rate and properties are influenced by meteorological conditions, parent soil, and landscape, and in turn, it affects impacts on climate, ecosystems, and human societies through various pathways. This dissertation aims to explore the coupled dynamics of dust particle emissions and their essential properties in relation to topography, ecosystem, and atmospheric conditions by integrating information across multiple scales. Specifically, three research projects are pursued. First, the modulation of dust emissions by non-photosynthetic vegetation (NPV) is evaluated by implementing a satellite-based total vegetation dataset, which includes NPV, into a regional atmospheric chemistry model. Simulations of the entire year 2016 over the conterminous United States demonstrate that NPV reduces dust emissions by 10-70% from most dust sources in the southwest, particularly in spring. Second, the relationship between topographic wind conditions (i.e., speed and direction with respect to surface slope) and dust particle size distribution is investigated using a decade's worth of dust reanalysis data covering North Africa. Findings indicate that the fraction of coarse dust in emissions increases with wind speed and slope, particularly under uphill winds, the latter highlighting the role of topography in enhancing vertical transport for larger particles. These positive correlations weaken during the afternoon and summer events, suggesting that turbulence associated with haboob events suspends coarse particles. Finally, a series of air samples collected in Tenerife, Spain is revisited for a detailed study on the associated dust plume characteristics, which would facilitate the understanding of how environmental factors during transport influence airborne microbial assemblages. Using back trajectory analysis and dust optical depth reanalysis data, air samples impacted by African dust are identified. Seasonal variations in trajectories and associated environmental conditions reveal highly variable trans-Atlantic airflows. Elevated altitudes, higher temperatures, and lower relative humidity (RH) along summer trajectories implied the presence of Saharan Air Layer, whereas the frequent occurrence of higher RH (> 40%) and light precipitation in spring indicate more deposition of dust and associated microbes during transport. Overall, this work highlights the importance of accurately representing of various environmental elements that interact with the dust cycle, such as vegetation and topographic winds, which improves our ability to predict and manage the impacts of dust as well as other components of the Earth system. / Doctor of Philosophy / Dust particles can be lifted by strong winds from dry lands, and they are a major contributor to the amount of particles in the air. Suspended dust particles can alter temperatures and weather patterns, reduce visibility, and cause health problems. When settling back to land or oceans, they can carry nutrients and microbes that influence the growth of plants and animals. The movement and properties of dust are subject to various elements of the environment, spanning from microscopic scale to global scale. This dissertation aims to explore the interactions between dust and a few of these environmental elements that are not well understood. Specifically, we first provide information about brown vegetation, which was previously lacking, to a dust model, and find that the dust emissions in the southwestern United States is reduced by 10-70%, particularly in spring. Second, we examine how the changes of wind over slopes influence the size of dust particles in the air by analyzing data for 10 years that combine information from models and satellite observations. We find that faster winds and uphill slopes lead to more large dust particles in the atmosphere. The third study analyzes the pathways of air samples from Africa to Tenerife, Spain, to understand how the transport of dust might affect the types of bacteria that travel with it across the ocean. We find that the airflows from Africa to Tenerife vary greatly from case to case, and the environmental conditions, such as precipitation and relative humidity, varying significantly across seasons and during the dust travel. Overall, this dissertation provides a deeper understanding of the complex ways dust interacts with our world, offering insights that can help us manage its impacts on climate, ecosystems, and human society more effectively.

No

Yes / N/A

The key to a successful wetland design is duplicating the hydroperiod of the desired wetland type. Dense wetland vegetation affects surface water flow rates by increasing flow resistance. Prior research represented the vegetation as individual stems; however, many wetland species grow in clumps. Therefore, the objectives of this study were to investigate the effect of clumping vegetation on flow resistance and to develop a prediction equation for use in wetland design. A 6-m by 1-m by 0.4-m recirculating flume was planted with mature common rush, Juncus effusus, a common emergent wetland plant. Three different flow rates (3, 4, and 5 L/s) and three different tailgate heights (0, 2.5, and 5 cm) were used to simulate a variety of wetland conditions. Plant spacing and clump diameter were varied (20 and 25 cm, 8 and 12 cm, respectively). Friction factors ranged from 9 to 40 and decreased with increasing plant density. Non-dimensional parameters determined through Buckingham Pi analysis were used in a regression analysis to develop a prediction model. Results of the regression analysis showed that the fraction of vegetated occupied area (P) was most significant factor in determining friction factor. / Master of Science