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.
More information is available at Theses and Dissertations at University of Maryland Libraries.
Browse
4 results
Search Results
Item Impact of salinity on morphology, growth, and pigment profiles of Scenedesmus obliquus HTB1 under ambient air and elevated CO2 (10%) conditions(2024) Jiao, Fanglue; Chen, Feng; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Certain microalgal species tolerate high CO2 concentrations and proliferate faster with elevated CO2 than with ambient air. This feature makes them attractive for carbon sequestration, a tool for mitigating climate change due to increasing atmospheric CO2. Scenedesmus species are among these microalgae. Scenedesmus obliquus strain HTB1 is a microalgal strain isolated from the Baltimore Inner Harbor (brackish water) and has shown a faster growth with 10% CO2 compared to air. However, how HTB1 grows under different salinity and if the salt response is affected by elevated CO2 remains elusive. Two experiments were set up to address these questions. The first experiment tested the impact of salinity gradient (0, 17.5, 20, 22.5, 25, 27.5, and 30 ppt) on HTB1 under ambient air. With increasing salinity, HTB1 cells became smaller, and the cultures changed color from green to brown, yellowish brown, and then to pale white. The pigment analysis showed that HTB1 reduced several pigments (i.e. zeaxanthin, lutein, chlorophyll b) in response to salt stress. However, HTB1 produced higher concentrations of canthaxanthin under the salt stress. The growth of HTB1 decreased with increasing salinity and was inhibited when the salinity was greater than 22.5 ppt. In the second experiment, we compared the impact of salinity (0, 10, and 20 ppt) on HTB1 under air and 10% CO2, respectively. HTB1 cultures showed little color change with increasing salinity under 10% CO2. In contrast, the change of culture color from dark green to brown was observed with increasing salinity when HTB1 was grown with air. Interestingly, the growth of HTB1 was less inhibited with salt under 10% CO2 than with air, suggesting that elevated CO2 mitigates the salt stress of HTB1. Lutein and canthaxanthin increased with increasing salinity when HTB1 was grown with 10% CO2. Our results indicate that increased salinity affects the growth of Scenedesmus obliquus HTB1 more with air than with 10% CO2. This study provides insight into the impact of salt stress on algal morphology, growth, and pigment composition.Item SOLUBLE SALTS REDUCTION AND METALS BEHAVIOR OF DREDGED SEDIMENT FOR REUSE IN HIGHWAY SLOPE APPLICATIONS(2019) Huffert, Michelle B; Davis, Allen P.; Aydilek, Ahmet H.; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Waterways are dredged routinely to maintain navigation channels, resulting in large quantities of dredged materials (DM) that require disposal. This study examines the innovative reuse of DM as a topsoil alternative in highway slopes. The dredged material met Maryland Department of Transportation, State Highway Administration (MDOT SHA) topsoil requirements for pH, organic matter, and particle size distribution, and required 122 cm (48 inches) of rainwater to leach soluble salts to below limits. Column leach tests were performed on DM and topsoil to evaluate metal leaching behavior; extractions were performed to determine total and potentially mobile metals content. DM leached metals concentrations below drinking water maximum contaminant levels (MCLs) for >95% of the samples tested, and passed a toxicity characteristic leaching procedure (TCLP). Extraction data showed higher total concentrations of arsenic, chromium, and lead as compared to topsoil, but similar concentrations in the EDTA-extracted fractions indicating that metals are strongly bound.Item Effects of Salinity on Settlement and Metamorphosis of the Eastern Oyster (Crassostrea virginica)(2016) Priester, Anna Priester; Meritt, Donald W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The eastern oyster (Crassostrea virginica) is a euryhaline species known for its historic populations, valuable fishery, and ecological importance. One of the most critical periods in the oyster’s life cycle is its transition from a free-swimming pelagic larva into its sessile benthic form. Despite the importance of this transition, which includes attachment to a substrate (settlement) and metamorphosis into the juvenile, our understanding of salinity tolerance during these processes is limited. This study was designed to quantify the effects of salinity on settlement and metamorphosis and to determine if those effects were influenced by the salinity in which the larvae were reared. Multiple cohorts of pediveliger larvae from hatcheries grown in Low (10), Medium (15-16.5) and High (22-27.5) salinities were allowed four days to settle in twelve salinity treatments ranging from 5 to 35. A set of additional experiments was extended to 14 days to investigate if the settlers were also able to complete metamorphosis and demonstrate juvenile growth within the same range of salinities. Settlement consistently occurred all tested salinities (5-35), indicating that pediveliger larvae can adapt to a broader salinity range than described in previous research. Highest settlement rates were achieved in treatment salinities between 11 and 30 for all three larval groups. Settlement performance outside that optimal range was highest for the larvae group reared in salinities closest to those extremes. Settlers from the 14-day experiments demonstrated metamorphosis and high post-settlement survivorship in all salinity treatments, but juvenile growth rates were reduced in salinities less than 9 and above 30. This highly repeated study reveals the impressive capacity for pediveliger larvae to tolerate a wide range of salinities and has direct implications for oyster aquaculture and our understanding of natural recruitment.Item Creating Marshes with Dredged Material on a Restored Island in Chesapeake Bay(2006-04-17) Mielcarek, Kristin C; Stevenson, J. C.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Tidal marsh creation using dredged materials could compensate for losses due to a variety of anthropogenic activities, including higher rates of sea-level rise. However, initial seeding attempts failed in a newly created marsh in Poplar Island, MD. Hypotheses were that soils were too acid, too saline, too high in sulfides or seeds were not viable. In test plots containing mostly sand, amendments of dredged materials enhanced plant growth and survival. Furthermore pH was between 5.5 and 7, not low enough to inhibit growth of marsh grasses. Sulfides in pore water were very low (<20>µM). Soil moisture content limited production in plants growing under long photoperiods in summer conditions. Seed germination was zero in Spartina patens and decreased significantly in Spartina alterniflora at salinities greater than 10 and biomass was greatest in plants grown in low salinities (2.5 and 5).