Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item Influences of wave climate and sea level on shoreline erosion rates in the Maryland Chesapeake Bay(2015) Gao, Jia; Sanford, Lawrence Paul; Boicourt, William C.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)SWAN and a parametric wave model implemented by the Chesapeake Bay Program (CBP) were used to simulate wave climate from 1985 to 2005 in Chesapeake Bay (CB). Calibrated sea level simulations from the CBP hydrodynamic model were acquired. Spatial patterns of sea levels during high wave events were dominated by local north-south winds in the upper Bay and by remote coastal forcing in the lower Bay. A dataset comprising shoreline erosion rates and related characteristics was combined with the wave and sea-level climates to explore the most influential factors affecting erosion. The results show that wave power is the most significant factor for erosion in the Maryland CB. Marsh shorelines present a nearly linear relationship between wave power and erosion rates, whereas bank shorelines are less clear. The results of this study are applicable at large scales. A more comprehensive data set is needed for building detailed local predictive relationships.Item PATTERNS OF WETLAND PLANT SPECIES RICHNESS ACROSS ESTUARINE RIVER GRADIENTS(2009) Sharpe, Peter James; Baldwin, Andrew H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)It is widely accepted that in coastal wetlands a negative relationship exists between plant species richness (number of species) and salinity. However, the distribution of species richness across estuarine salinity gradients has not been closely examined. I hypothesized that plant species richness in coastal marshes (i.e., wetlands dominated by herbaceous plants) would follow a non-linear pattern with increased distance (salinity) downriver (Chapter 2). To test this hypothesis I conducted detailed marsh vegetation surveys along ≈ 50 km estuarine river gradients of the Nanticoke and Patuxent Rivers, MD/DE. I further hypothesized that the observed patterns of plant species richness on the Nanticoke and Patuxent Rivers could be accurately predicted by a mid-domain effect (MDE) model independent of measured abiotic factors using RangeModel 5.0 (Chapter 3). Lastly, I theorized that Marsh mesocosms subjected to intermediate salinity and inundation would exhibit significantly higher biomass and plant species richness compared to mesocosms subjected to extreme salt/fresh and flooding regimes utilizing a controlled greenhouse experiment (Chapter 4). I found that plant species richness can vary in both a linear (Patuxent River) and non-linear (Nanticoke River) pattern along an estuarine gradient. The MDE model did not explain a high proportion of the observed richness patterns for either river system compared to abiotic factors like porewater salinity. The controlled marsh mesocosm experiment supported the non-linear pattern of plant species richness observed along the Nanticoke River gradient, but did not show a significant difference in plant biomass or richness/diversity between purely fresh and low-salinity marsh mesocosms (α = 0.05). The results of this research suggest that tidal marsh plant richness/diversity patterns do not always conform to a simple linear relationship with increasing salinity and that the MDE is not as important of a mechanism in these communities compared to porewater salinity or flooding frequency. Furthermore tidal low salinity marshes exposed to elevated salinity and flooding frequencies are likely to see a shift in their plant community structure to more salt tolerant plants and less rich/diverse communities assuming they can accrete at a rate equal to or exceeding the present rates of sea-level rise in the Chesapeake Bay.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).Item The effect of sea level rise on seagrasses: Is sediment adjacent to retreating marshes suitable for seagrass growth?(2005-12-13) Wicks, Elinor Caroline; Koch, Evamaria W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Salt marsh retreat resulting from sea level rise creates new subtidal substrate (old marsh peat) for seagrasses, which is usually unvegetated. The hypothesis that sediment characteristics of old marsh peat are limiting to <em>Zostera marina</em> was tested in Chincoteague Bay, Maryland and in controlled experiments. A unique aspect of the study site is an eroding dune within the marsh that supplies sand to the subtidal. The organic content and sulfide concentrations of old marsh peat were not limiting <em>Z. marina</em> growth and seagrasses were able to colonize the old marsh peat if a layer of sand covered it. The lack of <em>Z. marina<em/> in old marsh peat may be due to a plant morphology that is highly susceptible to dislodgement. These findings suggest that seagrass distribution may be negatively affected by sea level rise as seagrasses may be unable to migrate shoreward due to unsuitable sediments adjacent to retreating marshes.Item Wetland Restoration in Urban Settings: Studies of Vegetation and Seed Banks in Restored and Reference Tidal Freshwater Marshes(2005-12-12) Rusello, Kristin; Baldwin, Andrew H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study examined the seed bank and vegetation of a restored tidal freshwater marsh located in Washington, D.C. and compared it to an older restored marsh, a natural urban marsh, and a natural non-urban marsh. A study examining the effects of a beaver impoundment on the vegetation and edaphic factors in the natural non-urban reference site was also conducted. The number of seedlings, vegetation cover, taxa density, evenness, and diversity of vegetation were compared among sites in these studies. The restored marshes were more similar to the natural urban wetland than to the natural non-urban wetland with regard to the seed bank and vegetation. Duration of flooding from the beaver impoundment was found to be an important factor affecting vegetation composition at the non-urban reference site. Findings included: urban restoration projects should likely have urban reference sites; and natural disturbances may have similar influences upon both natural and restored systems.