Theses and Dissertations from UMD
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Item ASSESSING THE IMPACTS OF ORGANIC AMENDMENTS ON DISTURBED SOIL PROPERTIES, WATER QUALITY AND VEGETATION GROWTH(2024) Pamuru, Sai Thejaswini; Davis, Allen P; Aydilek, Ahmet H; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Deficiencies in essential organic matter (OM) are exhibited in disturbed roadside soils rendering them less favorable for plant growth. Vegetation plays a crucial role in maintaining the health of ecosystems, providing a myriad of benefits in protecting against soil erosion and effectively managing stormwater. National and state transportation departments are therefore prioritizing roadside vegetation using sustainable practices, leading to increased use of organic amendments (OAs) such as compost or related materials. OAs are commonly recycled and repurposed materials that serve as valuable soil conditioners, and their characteristics vary depending on their parent materials. Many OAs are cost-effective, readily available, and offer significant benefits to urban soils, which often are bereft of plant-essential nutrients and stability. This necessitates a better understanding of their impact on soil health and the environment, when applied at “acceptable” rates. This research aims to explore soil-water-plant interactions in urban soils (with and without OAs) focusing on vegetation establishment, soil fertility, and nutrient transport via leaching/runoff. Greenhouse and laboratory experiments were conducted to assess the potential use of these OAs for roadside projects.One set of experiments (greenhouse tub studies) focused on three OAs (leaf compost, shredded aged wood mulch, biosolids) which are widely available across Maryland. The amended soils were mixed to meet the topsoil OM requirements (4 – 8 %) of the state. Water quality results highlighted that the biosolids, while effective in retaining influent rainwater (tap water) phosphorus, caused significant nitrogen losses, exceeding typical stormwater concentrations by 40-200 times. Leaf compost also contributed to nitrogen leaching but only during the initial stages. Mulch reduced nutrient loss but caused limited vegetative cover. The study found that soil properties, such as the carbon-to-nitrogen (C:N) ratio and nitrogen content, play a vital role in the magnitude and patterns of nitrogen leaching. Additionally, it was speculated that the presence of soil minerals, such as iron and calcium, successfully retained phosphorus in the amended soils. The shear and hydraulic properties of the soils improved with the incorporation of amendments. Based on the results of the tub studies, leaf compost identified as a suitable OA for plants and water quality. However, the tub studies had limitations in their evaluation of compost amendments derived from different feedstock sources and their impacts on native vegetation growth. Therefore, a pot study was conducted to determine the optimum mixing ratios of soils and OAs to facilitate rapid vegetation growth. Three types of composts (turkey litter, food waste and yard waste) with varying nutrient properties were tested. A wood-based biochar was the fourth chosen OA because of its valuable use in agriculture and environmental remediation. The findings showed that turkey litter compost severely inhibited growth at higher application rates due to excess salts content. However, this compost showed improved plant nitrogen and leaf area whenever vegetation was established. Alternatively, biochar, while not inhibiting growth, resulted in visibly weak plant morphology, and led to nitrogen deficiencies. Yard waste and food waste composts showed positive impacts in terms of coverage, leaf area index and plant N contents. Between the tub studies and the pot study, yard waste compost has consistently emerged as the favorable soil amendment. Given biochar’s well documented advantages for water quality and soil structural properties, a scaled-up mesocosm experiment that simulated sloped road shoulders was conducted to test the effectiveness of combining compost and biochar in urban soils, aiming to meet vegetation and water quality goals. The runoff phosphorus and nitrogen mass transports were highest (261 mg-P/m2 and 8645 mg-N/m2, respectively) when compost was the sole amendment mixed into the control soil. However, adding biochar to the soil reduced these losses by up to 5.6x for phosphorus and 8.8x for nitrogen compared to compost. Strong correlation between soil C:N and effluent N was noted, higher ratios (>20:1) reduced nitrogen losses. Biochar, due to its high carbon content and pH, also helped retain phosphorus in the soils. Conversely, compost, being more readily decomposable than biochar, caused nutrients to run off. Compost-biochar mixtures also showed greater plant growth compared to the control soil. Together, this research shows that not all high-nutrient OAs provide favorable outcomes when incorporated into soils to enhance the OM content. Leaf or yard waste-based composts are preferred for roadside vegetation due to their reduced issues related to nutrient losses compared to other nutrient-rich materials tested in this study. However, the yard waste compost incorporation rate should be limited to achieve a soil OM increase of 1-2% to prevent high nutrient levels in the runoff. Furthermore, combining biochar and yard waste compost offers a promising approach for construction projects particularly on steep terrains to achieve and preserve a balanced soil-water-plant ecosystem.Item ADDRESSING THE IMPACT ON SOIL DEGRADATION OF CHANGE FROM GRASSLAND TO CROPLAND: A CASE STUDY IN THE URUGUAYAN GRASSLANDS(2017) Castano-Sanchez, Jose P; Prince, Stephen D; Izaurralde, Roberto C; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Globally, there has been large-scale conversion of natural grassland to cropland ecosystems which this has led to land degradation that could reduce future food security, other ecosystem services and even climate. Currently, there is a dearth of quantitative information assessing the severity, distribution, and causes of this land degradation. For practical purposes, this information is needed to develop improved methods of land use (LU) conversion. Uruguay, in contrast with many other regions, still has a high proportion of unimproved grasslands but, during the last 15 years, there has been extensive conversion to grow grain crops. The fundamental goal of this dissertation was to quantify soil degradation resulting from this LU change. Two aspects of soil degradation were studied, soil organic carbon (SOC) and erosion by water. The Environmental Policy Integrated Climate biophysical simulation model (EPIC) was used to model the grassland and cropping systems. The study consisted of three steps: (1) calibration and validation of the model for the Uruguayan agroecosystems, and development of a spatial version, (2) identification of the LU change areas, and (3) quantification of soil degradation as a result of the LU changes. The EPIC model adequately reproduced the field-scale SOC dynamics and erosion in field validation sites. Further, the spatial version of the model was found to simulate spatial and temporal performance adequately. LU change areas during 2000-2013 were mapped and found to cover an area of 410,000 ha, about 13% of potential area for commercial agriculture. LU greatly affected soil degradation. It was greatest for continuous Soybean cultivation with no crop rotation, and lowest for grassland (no conversion to cropping). In addition to LU, slope and initial SOC had significant effects on degradation. The main conclusions were that the recent and continuing conversion from grassland to cropland has caused significant soil degradation, but that some modifications of LU can reduce the risk of degradation.Item A particle erosion model of monocrystalline silicon for high heat flux microchannel heat exchangers(2017) Squiller, David; McCluskey, Patrick; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)As package-level heat generation pushes past 1 kW/cm3 in various military, aerospace, and commercial applications, new thermal management technologies are needed to maximize efficiency and permit advanced power electronic devices to operate closer to their inherent electrical limit. In an effort to align with the size, weight and performance optimization of high temperature electronics, cooling channels embedded directly into the backside of the chip or substrate significantly reduce thermal resistances by minimizing the number of thermal interfaces and distance the heat must travel. One implementation of embedded cooling considers microfluidic jets that directly cool the backside of the substrate. However, as fluid velocities exceed 20 m/s the potential for particle erosion becomes a significant reliability threat. While numerous particle erosion models exist, seldom are the velocities, particle sizes, materials and testing times in alignment with those present in embedded cooling systems. This research fills the above-stated gaps and culminates in a calibrated particle-based erosion model for single crystal silicon. In this type of model the mass of material removed due to a single impacting particle of known velocity and impact angle is calculated. Including this model in commercial computational fluid dynamics (CFD) codes, such as ANSYS FLUENT, can enable erosion predictions in a variety of different microfluidic geometries. First, a CFD model was constructed of a quarter-symmetry impinging jet. Lagrangian particle tracking was used to identify localized particle impact characteristics such as impact velocity, impact angle and the percentage of entrained particle that reach the surface. Next, a slurry erosion jet-impingement test apparatus was constructed to gain insight into the primary material removal mechanisms of silicon under slurry flow conditions. A series of 14 different experiments were performed to identify the effect of jet velocity, particle size, particulate concentration, fluid viscosity and time on maximum erosion depth and volume of material removed. Combining the experimental erosion efforts with the localized particle impact characteristics from the CFD model enabled the previously developed Huang et al. cutting erosion model to be extended to new parameter and application ranges. The model was validated by performing CFD erosion simulations that matched with the experimental test cases in order to compare one-dimensional erosion rates. An impact dampening coefficient was additionally proposed to account for slight deviations between the CFD erosion predictions and experimental erosion rates. The product of this research will ultimately enable high fidelity erosion predictions specifically in mission-critical military, commercial and aerospace applications.Item Influences of wave climate and sea level on shoreline erosion rates in the Maryland Chesapeake Bay(2015) Gao, Jia; Sanford, Lawrence Paul; Boicourt, William C.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)SWAN and a parametric wave model implemented by the Chesapeake Bay Program (CBP) were used to simulate wave climate from 1985 to 2005 in Chesapeake Bay (CB). Calibrated sea level simulations from the CBP hydrodynamic model were acquired. Spatial patterns of sea levels during high wave events were dominated by local north-south winds in the upper Bay and by remote coastal forcing in the lower Bay. A dataset comprising shoreline erosion rates and related characteristics was combined with the wave and sea-level climates to explore the most influential factors affecting erosion. The results show that wave power is the most significant factor for erosion in the Maryland CB. Marsh shorelines present a nearly linear relationship between wave power and erosion rates, whereas bank shorelines are less clear. The results of this study are applicable at large scales. A more comprehensive data set is needed for building detailed local predictive relationships.