UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
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Item Management of Ammoniacal Nitrogen in Stormwater Runoff(2016) Khorsha, Golnaz; Davis, Allen P; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Nitrogen in stormwater runoff plays a dominant role in the eutrophication of receiving waters. The challenge in treating nitrogen lies in its diverse speciation and biological cycling. This work aimed to improve removal of influent and mineralized ammonium through the use of sorption media and nitrification in preparation for subsequent denitrification. Two media, clinoptilolite (ZT) and hydrous-aluminosilicate (CA), were characterized in a series of batch and sorption column experiments, which indicated superior performance of ZT because of its higher capacity (206 months life-expectancy) and faster kinetics (60 min). Competition with Ca2+ and K+ resulted in smaller and slower sorption for both media. Removed ammonium in ZT was highly extractable, signifying its potential bioavailability. Sorption columns exhibited high removal during influent NH4+ increases, desorption with influent concentration drops, and lower ammonium removal upon rewetting/saturateting. Nitrification in bio-active sorptive media enhanced removal efficiency, particularly for alternating wet/saturated-dry/unsaturated conditions, with smaller desorption occurring. ZT application in filtration-based stormwater control measures is recommended.Item EFFECT OF COMPOST ON THE MICROCLOVER ESTABLISHMENT AND USE OF COMPOST AND MICROCLOVER TO REDUCE LAWN NUTRIENT RUNOFF(2016) Xiao, Xiayun; Carroll, Mark; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)High volume compost incorporation can reduce runoff from compacted soils but its use also associated with elevated N and P concentrations in runoff making it difficult to assess if this practice will reduce nutrient loading of surface waters. Additionally, little is known about how this practice will effect leguminous species establishment in lawns as means to reduce long term fertilizer use. When 5 cm of compost was incorporated into soil a reduction in runoff of 40 and 59% was needed for N and P losses from a tall fescue + microclover lawn to be equivalent to a non-compost amended soil supporting a well fertilized tall fescue lawn. Use of compost as a soil amendment resulted in quicker lawn establishment and darker color, when compared to non-amended soil receiving a mineral fertilizer. Biosolid composts containing high amounts ammonium severely reduce the establishment of clover in tall fescue + micrclover seed mixture.Item The comparative effects of three Sedum species on green roof stormwater retention(2013) Starry, Olyssa; Lea-Cox, John; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Green roofs are typically dominated by Sedum species because they can tolerate hot, xeric environments. However, due to their high water use efficiency, some have questioned the selection of these species for stormwater management. We investigated (1) how three common Sedum species contribute to overall stormwater retention efficiency by green roofs in the mid-Atlantic region, and (2) whether species-specific differences in water use could be explained by morphological and physiological characteristics. Water use and CO2 exchange were continuously monitored in growth chamber studies under increasing drought stress for S. album, and S. kamtschaticum, two species known to variably cycle between CAM and C3 metabolisms. Under fall temperature conditions, S. kamtschaticum had gas exchange rates akin to C3 photosynthesis and used 35% more water compared to S. album. Interestingly, S. album conserved water and had malic acid accumulation confirming CAM metabolism for the duration of the experiment, even under well-watered conditions. In field studies, sixteen replicate green roof platforms (n=4 per species) were planted with S. album, S. kamtschaticum, S. sexangulare, or left unplanted during summer 2010. The platforms were monitored intensively for canopy growth, leaf area, root biomass, substrate moisture and runoff for two years (2011 and 2012). Plant treatment effects on stormwater runoff were significant, but most discernible for small and intermediate-sized rainfall events less than 62.5mm. The two species with the greatest stormwater retention efficiencies, S. kamtschaticumand S. sexangulare, also had the highest rates of evapotranspiration (ET), and higher ET rates resulted in less total runoff. Because evapotranspiration was identified as important for predicting performance by plants in the field study, I investigated how ET data from this study, combined with environmental data collected from a weather station at the study site, could be used to improve the application of the FAO56 Penman-Monteith evapotranspiration equations to green roofs. The incorporation of specific seasonal crop coefficients were found to improve correlations between predicted and measured rates of ET and these coefficients were related to plant characteristics. The refinement of ET equations can lead to more accurate hydrologic models of green roofs and design and management tools.Item Treatment of Stormwater Runoff by Geotextile Filters via Suspended Solids Capture(2012) Franks, Carmen; Davis, Allen P; Aydilek, Ahmet H; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Suspended solids in stormwater runoff create a range of water quality problems; their removal lessens the deleterious impact of stormwater runoff on aquatic ecosystems. In this study, three geotextiles were tested in laboratory column tests with influent suspensions having hydraulic loading rates, total suspended solids (TSS) concentrations, and particle size distributions (PSDs) similar to those reported for urban highway stormwater runoff. After a short ripening period, the geotextile filters removed TSS from 100-200 mg/L to below a target concentration of 30 mg/L. A lower geotextile permittivity resulted in an increased percentage of TSS captured by the filter; however, the total mass of solids captured was unaffected because lower permittivity resulted in lower total solids loaded to the filter overall. In general, the effectiveness of the geotextile filter at retaining suspended solids increased as filter opening sizes decreased and as influent particle sizes increased. The hydraulic conductivity of a geotextile filter, which was related to TSS captured via a power function, was higher for geotextiles with higher permittivity and larger opening sizes and for larger influent particle sizes. Overall, the filter with the second highest permittivity (0.8 s-1), NW2, was the most successful geotextile tested. TSS removal in the geotextile laboratory tests was comparable to reported values from sand filters in literature under similar loading conditions. Sand filters in laboratory tests had greater TSS removal than geotextile filters. However, the sand filters clogged at a lower total solids loading than the geotextiles. The applicability of existing filtration criteria for geotextiles for stormwater treatment is addressed, and four new retention criteria ratios specifically for stormwater filtration which use two filter opening sizes and two particle diameters, such as (095/D60)/(O30/D10) > 0.05, are introduced. Results from field testing are analyzed; the geotextile filter reduced TSS concentrations in runoff by an average of 84% with input TSS event mean concentrations (EMCs) ranging from 22 - 185 mg/L and output EMCs ranging from 1.7 - 22 mg/L. A mathematical model is developed which estimates hydraulic conductivity as a function of solids captured. The model and filtration criteria are used to assess the field testing results.