Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item Discerning the roles of ocean acidification, eutrophication, and river alkalization in driving long-term pH trends in the Chesapeake Bay(2022) Guo, Yijun; Li, Ming; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Rising anthropogenic CO2 in the atmosphere and oceanic uptake of CO2 have led to a gradual decrease in seawater pH and ocean acidification, but pH changes in estuaries and coastal systems are more complicated due to a multitude of global and regional environmental drivers. Increasing global fertilizer use due to agricultural production has led to a doubling of riverine nutrient loading since the 1950s, leading to widespread eutrophication in estuarine and coastal waters. Excessive nutrient loading stimulates primary production in the surface euphotic layer, which consumes CO2 and elevates pH, but unassimilated organic matter sinks and decomposes in bottom waters, producing CO2 and reducing pH. In the meantime, human-accelerated chemical weathering, such as acid rain and mining, has resulted in rising alkalinity in many rivers and basification in estuarine and coastal waters. To discern how these environmental drivers influence long-term pH trends in coastal waters, a coupled hydrodynamic-biogeochemical-carbonate chemistry model was used to conduct hindcast simulations of the Chesapeake Bay between 1951 and 2010. The model reproduced the observed chlorophyll increase and hypoxia expansion due to the increased nutrient loading. In contrast, low-pH bottom waters and acidic volume shrank from 1950 to 1980. GAM analysis of long-term pH trends in different regions of Chesapeake Bay revealed increasing pH in the upper Bay driven by the river alkalinization, a peak pH in the mid-Bay in the 1980s coincident with the peak nutrient loading and decreasing pH in the lower Bay driven by ocean acidification. Four scenario runs were performed to assess the individual effects of rising pCO2, river alkalinization, riverine nutrient loading, and climate change (warming and sea-level rise) on long-term pH changes in the Chesapeake Bay. The model results suggested that river alkalinization was more important than ocean acidification in driving the long-term pH changes in the estuary.Item YOUNG FOREST MANAGEMENT FOR SENSITIVE BIRD SPECIES IN WESTERN MARYLAND(2020) Taillie, Dylan Maher; Elmore, Andrew J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Golden-winged warbler, cerulean warbler, and wood thrush populations are in decline in the eastern United States. Golden-winged warblers rely on young forests – such as those created using silviculture – for nesting and early life stages; however, the loss of late-successional forest through timber harvest likely degrades habitat for cerulean warblers and wood thrush. To quantify these complexities, I mapped current habitat quality for these three species in Western Maryland using models based on forest metrics. The creation of young forest through silviculture and field succession scenarios was then simulated to project how modeled changes affect predicted habitat quality. Field succession scenarios and silviculture scenarios both improved predicted habitat quality for golden-winged warblers and wood thrush; however, for cerulean warblers, field succession scenarios improved habitat quality while silviculture scenarios degraded habitat quality. This modeling approach will assist managers in using funds to simultaneously improve habitat quality for multiple sensitive species.Item EXURBAN DEVELOPMENT: QUANTIFICATION, FORECAST, AND EFFECTS ON BIRD COMMUNITIES(2011) Suarez-Rubio, Marcela; Lookingbill, Todd R; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Rural landscapes in the United States have changed dramatically in recent decades due to the rapid development of private rural lands into low-density residential exurban development. This land conversion is a rising cause of concern due to its potential effects on biodiversity and ecosystem processes. Although exurbanized area is thought to have a significant increase in eastern deciduous forests, a rigorous assessment of exurban trends, drivers, and ecological consequences has yet to be undertaken. First, I develop a novel analytic approach to identify exurban areas and assess how much land has been converted to exurban development in the Mid-Atlantic region. The approach describes mixed pixels containing exurban development as a combination of land covers and uses decision-tree classification and morphological spatial pattern analysis to further separate exurban development from other forest disturbing events. The results indicate that exurban development is a pervasive and fast-growing form of land use in the region. Second, I evaluate the effectiveness of two contrasting modeling approaches in capturing exurban growth at a local and county scale. Exurban growth was effectively captured by the spatially-explicit econometric model at both scales and the pattern-based model only performed well at the county scale. Thus, pattern-based models like SLEUTH can forewarn potential coarse-scale losses of natural resources in exurban areas, but are less useful at finer scale or for assessing potential impacts of implementing land-use policies. Third, I assess whether exurban development degrades avian breeding territories over time and forest birds' response to those changes. I conclude that exurban development is degrading breeding habitats by reducing forest cover and increasing habitat fragmentation. Forest birds exhibited a threshold response to deteriorating breeding habitats in the vicinity of breeding territories and adjacent foraging areas being forest specialists the most sensitive group. To avoid the likelihood of sudden bird population declines amongst further habitat loss and fragmentation, a synergy among land managers, planners, and decision-makers will become increasingly important to mitigate the impacts of exurban development in the Mid-Atlantic region.Item An Ecological Perspective of the Energy Basis of Sustainable Bolivian Natural Resources: Forests and Natural Gas(2008-04-29) Izursa, Jose-Luis; Tilley, David R.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Bolivia, traditionally known for being a country rich in natural resources, has suffered from a constant exploitation of its natural resources benefiting only small groups in and outside the country. The devastation of natural resources that occurred for many years was of concern to the latest government, rural communities and indigenous groups. As a result, Bolivia has a more sustainability-oriented forest law that has a strong orientation towards the utilization of natural resources at a national level and encompasses a fast-growing forestry industry than in previous years. In this dissertation, the wealth of Bolivia's national system was evaluated using solar emergy. Emergy (spelled with "m") is the sum of all energy of one form needed to develop a flow of energy of another form, over a period of time. The basic idea is that solar energy is our ultimate energy source and by expressing the value of products in solar emergy units, it becomes possible to compare different kinds of energy, allowing to express the value for the natural resources in Emergy Dollars. It was found out that Bolivia relies heavily in its natural resources and that its emergy exchange ratio with its international trading partners changed from 12.2 to 1 in 2001 to 6.2 to 1 in 2005. This means that Bolivia went from export 12.2 emdollars of goods for each $1 it received in 2001 to export 6.2 emdollars of products for each $1 it received in 2005. The study also showed that under forest certification practices less emergy is removed from forests (1.49E+19 sej/yr) compared to the amount of emergy removed (2.36E+19 sej/yr) under traditional uncertified practices, reflecting that forest ecology does better under certification. The "Ecologically-based Development for the Bolivian Industrial Forestry System" (DEBBIF) simulation model constructed during this study, compared four different scenarios: the Reference Scenario, the Increased Export Scenario, the Increased Domestic Use Scenario and the National Industrialization Scenario. Using two different levels of increment for each scenario, the outcomes of six variables were analyzed: soil, wood, natural gas, assets, money and debt. It was found that if the country doubles its use of natural resources to generate finished products, this will build more assets for Bolivia, and represent more income for the country and a better rate of emergy per person.