Theses and Dissertations from UMD
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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 give thesis/dissertation in DRUM
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Item LONG-TERM IMPACTS OF AMAZON FOREST DEGRADATION ON CARBON STOCKS AND ANIMAL COMMUNITIES: COMBINING SOUND, STRUCTURE, AND SATELLITE DATA(2020) Rappaport, Danielle I; Dubayah, Ralph; Morton, Douglas; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Amazon forest plays a vital role in the Earth system, yet forest degradation from logging and fire jeopardizes carbon storage and biodiversity conservation along the deforestation frontier. Polices to reduce forest carbon emissions (REDD+) will fall short of their intended goals unless carbon and biodiversity losses from forest degradation can be monitored over time. Emerging remote sensing tools, lidar and ecoacoustics, provide a means to monitor carbon and biodiversity across spatial, temporal, and taxonomic scales to address data gaps on species distributions and time-scales for recovery. This dissertation draws from a novel multi-sensor perspective to characterize the long-term ecological legacy of Amazon forest degradation across a 20,000 km2 landscape in Mato Grosso, Brazil. It combines high-density airborne lidar, 1100 hours of acoustic surveys, and annual time series of Landsat data to pursue three complementary studies. Chapter 2 establishes the bedrock of the investigation by using fine-scale measurements of structure sampled across a large diversity of degraded forests to model the initial loss and time-dependent recovery of carbon stocks and habitat structure following fire and logging. Chapter 3 models the interactions between sound and structure to predict acoustic community variation, and to account for attenuation in dense tropical forests. Lastly, Chapter 4 uses sound to go beyond structure to identify the specific degradation sequences and pseudo-taxa that give rise to variation in the ‘acoustic guild’ over time. Soundscapes reveal strong and sustained shifts in insect assemblages following fire, and a decoupling of biotic and biomass recovery following logging that defy theoretical predictions (Acoustic Niche Hypothesis). The synergies between lidar and acoustic data confirm the long-term legacy of forest degradation on both forest structure and animal communities in frontier Amazon forests. After multiple fires, forests become carbon-poor, habitats become simplified, and animal communication networks became quieter, less connected, and more homogenous. The combined results quantify large potential benefits to protecting already-burned Amazon forests from recurrent fires. This dissertation paves the way for greater integration of remote sensing and analysis tools to enhance capabilities for bringing biomass and biodiversity monitoring to scale. Building on this research with species-level and multi-temporal measurements will reduce uncertainty around the breakpoints that drive carbon and biodiversity loss following degradation.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.