Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item HYDROLOGY, SOIL REDOX, AND PORE-WATER IRON REGULATE CARBON CYCLING IN NATURAL AND RESTORED TIDAL FRESHWATER WETLANDS IN THE CHESAPEAKE BAY, MARYLAND, USA(2017) Keshta, Amr El Shahat Sedik; Baldwin, Andrew H; Yarwood, Stephanie A; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Tidal freshwater wetlands are key sites for carbon (C) sequestration and main component in the global C budget. The overall research objective of my dissertation was to examine the physical and biogeochemical processes that impact C cycling in tidal freshwater wetlands. One natural and one restored tidal freshwater wetland (salinity < 0.3 ppt) were selected in Maryland, USA along the Patuxent River. Data logging water recorders were installed in wells at each habitat in February 2014 for monitoring water level at 10-minutes interval and for two years. Soil organic matter and C stocks were estimated and a novel soil C bioassay (CARBIO) was developed and tested to assess C stability (change of soil organic matter concentration over time) and decomposition rates in both sites. A total of 162 CARBIO units were deployed in the natural and restored sites, and 81 were retrieved after 1 year while the others were retrieved after 2 years. Static chambers were used to quantify methane (CH4) and carbon dioxide (CO2) flux rates during day and nighttime. My results indicated that the natural wetland had significantly higher soil C stocks than the restored site (14.8±0.50 and 8.9±0.99 kg C m-2, respectively, P <0.0001). The swamp habitat had the highest soil organic matter (36.8%), while restored mudflat has the lowest (2.8%). Higher soil organic matter was partially correlated with shallower groundwater level relative to soil surface. Soil redox data with soil pH indicated that the soil of the natural wetland habitats was more reducing than the soil at the restored habitats. Based on CARBIO index, the soils in CARBIO units that were deployed in the natural wetland was significantly higher in C sequestration rate than the restored wetland (535±291.5 and -1095±429.4 g C m-2 year-1, respectively, P site<0.05). Under the current hydrological conditions, the restored wetland habitats were not able to accumulate C inside the CARBIO units after 1 or 2 years from deployment. In-situ CARBIO units can be employed in the newly constructed wetlands as in-situ sensors that reflect the C biogeochemical processes in the ambient soil to help better understanding C stability. The restored wetland had significantly higher annual CH4 emission rates than the natural wetland (1372.1±35.89 and 880.7±144.73 g CH4 m-2 y-1, respectively, P <0.05) and the log CH4 flux rate had a significant and strong negative correlation with the pore-water total available iron. Nighttime CH4 fluxes had very low concentration (<3650 µmole m-2 h-1). Future restoration efforts should focus on soil properties that will help increase C accumulation in newly constructed wetlands, but even more important every effort should be made to conserve the natural wetlands so that ecosystem function and services including wildlife habitat, water quality improvement, and offsetting the greenhouse gas emissions are maintained.Item EVALUATING RESTORATION POTENTIAL AND STORM SURGE ATTENUATION IN DITCHED AND UNDITCHED COASTAL MARSHES(2017) Lundberg, Dorothea June; Prestegaard, Karen; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The effects of ditching on the hydrological regime and ecosystem services of ditched coastal marshes—as well as the effects of hydrologic restoration of these systems—have yet to be extensively studied. The goals of this project were (1) to determine differences between ecohydrological processes in Ditched and Unditched coastal marshes, (2) to determine the effects of ditch plugging restoration projects on Atlantic Coast and Chesapeake Bay marsh hydrology, and (3) to evaluate Hurricane Sandy storm surge in the coastal marshes. Two separate pairs of Ditched and Unditched marshes were used in this study. The paired sites were adjacent, with similar topography, vegetation, and tidal patterns. Data collection included hydrological properties such as ditch density, tidal stage, water table fluctuations; as well as soil properties. Soil properties were similar in Ditched and Unditched marshes, while ditched marshes had lower water table elevations than Unditched marshes. Ditch plugging restoration partially restored the hydrological regime. A comparison of Chesapeake and Atlantic coastal marshes during Hurricane Sandy indicated similar storm surge elevations, but shorter durations of inundation at the Chesapeake Bay marshes when compared with the Atlantic marshes.Item Comparison of Hydrologic and Hydraulic Characteristics of the Anacostia River to Non-Urban Coastal Streams(2016) McDowell, Mallori; Prestegaard, Karen L; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Streams in urban areas often utilize channelization and other bank erosion control measures to improve flood conveyance, reduce channel migration, and overbank flooding. This leads to reductions in evapotranspiration and sediment storage on floodplains. The purpose of this study is to quantify the evapotranspiration and sediment transport capacity in the Anacostia Watershed, a large Coastal Plain urban watershed, and to compare these processes to a similar sized non-urban watershed. Times series data of hydrologic and hydraulic changes in the Anacostia, as urbanization progressed between 1939-2014, were also analyzed. The data indicates lower values of warm season runoff in the non-urban stream, suggesting a shift from evapotranspiration to runoff in urban streams. Channelization in the Anacostia also increased flow velocities and decreased high flow width. The high velocities associated with channelization and the removal of floodplain storage sites allows for the continued downstream transport of sediment despite stream bank stabilization.Item Importance of channel networks on nitrate retention in freshwater tidal wetlands, Patuxent River, Maryland(2009) Seldomridge, Emily Dawn; Prestegaard, Karen; Cornwell, Jeffrey C; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Freshwater tidal marshes border stream channels near the upstream end of the tidal limit, and are likely to undergo significant changes in salinity, tidal inundation, and biogeochemical processes due to sea-level rise. Tidal channel networks enhance nutrient processing by delivering nitrate-rich water far into the marsh. The purpose of this study is to examine the geomorphological, hydrological, and biogeochemical processes that influence the delivery and processing of nutrient-rich waters into tidal marshes. In this study, field measurements were made to calculate water and nitrate flux for stream channels of varying order. These mass balance calculations indicate there is an exponential increase in net nitrate retention with channel order. This calculation could be compared with calculations of denitrification at different sites within the system to evaluate the role of these processes in total nitrate loss.Item Hydrologic and Biogeochemical Storm Response in Choptank Basin Headwaters(2008) Koskelo, Antti; Fisher, Thomas R; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study quantified the effect of hydric soils on the hydrology and biogeochemistry of sub-watersheds across the Delmarva Peninsula. For hydrology, long-term data were compiled for 13 United States Geological Survey sites and evaluated for hydric soil effects. Results show that hydric soils reduce baseflow by increasing ponding and subsurface water storage, resulting in greater evapotranspiration. In contrast, hydric soils were unrelated to stormflow, which was instead driven by topography. During hourly sampling of 18 storms in the Choptank Basin, most forms of nitrogen and phosphorus increased in concentration due to erosion and re-suspension of sediments. Nitrate, however, decreased during storms due to dilution of nitrate-rich groundwater by runoff. Baseflow nitrate concentrations decreased with forested hydric soils, likely due to greater denitrification in forested hydric areas. Annually, much of the total nitrogen and phosphorus export occurred during storms, emphasizing the need to sample a wide range of flows to improve estimates of nutrient losses.Item Effect of Initial Soil Moisture Conditions on Runoff Transport of Manure-borne Pathogens through Vegetated Filter Strips(2006-11-21) Cardoso-Gendreau, Fatima Araujo; Shirmohammadi, Adel; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Pollution of drinking and recreational water supplies with manure-borne pathogenic bacteria through surface runoff from agricultural lands is a public health threat, particularly, where there is concentrated animal production (e.g., Iowa). This study was conducted to investigate the effect of initial soil moisture conditions on the effectiveness of vegetated filters strips (VFS) to mitigate surface runoff transport of two surrogate pathogenic bacteria, Escherichia coli and Salmonella enterica enterica Typhimurium, from land-applied swine slurry. A 5% slope lysimeter containing clay loam soil was constructed, partitioned into vegetated and bare plots, and the plots instrumented to collect, measure, and sample runoff at different time intervals and at two distances from the slurry application area during rainfall simulations. Results indicated that the potential of VFS to attenuate runoff transport of pathogens was reduced under increased initial soil moisture conditions, indicating that infiltration is an important factor in the mitigation process.