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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

A comparison of the biogeographical and geomorphological characteristics of gullied and non-gullied valley head mires in eastern Lesotho

Deschamps, Christine L. 11 November 2008 (has links)
Environmental degradation is a serious problem in Lesotho, Africa. The majority of studies dealing with soil loss and gully erosion have mainly focused on the mechanics of the erosion. However, mountain watersheds are sensitive and vulnerable to degradation and in so being, have large inherent environmental implications. Gully erosion diversifies the micro-topographical and hydrological environment. The severe changes and eventual system degradation incurred as a result of gullying has rarely been quantified. This paper specifically highlights mire phytogeographic responses to valley head degradation at selected sites in eastern Lesotho by comparing patterns observed in gullied mires to those seen in other non-gullied mires. Soil and vegetation belt transects are set up across five mires (2 gullied) in the highlands of eastern Lesotho. The response of many of the plant species to the overall environmental gradient was asymmetrical and unimodal in pattern. The spatial distribution of the soil’s physical properties, topography and vegetation community patterns were found to reflect the spatial mosaic of the soil moisture gradient. The negative impact that gullying has on the ecohydrological regime of the valley heads is evident and is allowing for shrub encroachment. Both the wetland and dryland vegetation communities correlate strongly with the changes in the surface soil moisture gradient. Gully erosion is clearly a threshold phenomenon. Continued grassland degradation, accelerated soil erosion and subsequent gullying of the wetlands will lead to plant and animal diversity loss, decreased livestock productivity, sediment-laden water and shortened dam life-span.
12

A Quaternary climate record from a Uinta Mountains, USA, fen core with emphasis on sediment pyrolysis

Hillam, Samuel Abraham 01 March 2017 (has links)
The northern slopes of the Uinta Mountains, Utah were previously glaciated and contain many landslides. The Tokewanna Landslide is very large and lacks Quaternary faults. Presumably, increased moisture was the failure trigger. A Quaternary climate record from a cored fen, developed in a small basin between hummocks, was reconstructed using sediment pyrolysis, biomass balance, and magnetic susceptibility. Pyrolysis is used to define Hydrogen Indices that are used to delineate wetter and drier conditions based on the kerogen type - Type III being drier, and Type II wetter. The data were matched to a time/depth curve and compared to other Uinta Mountains climate studies. Pyrolysis, biomass balance, and magnetic susceptibility results indicate drier to wetter conditions from ~11,027 to ~8,800 cal yr BP. This was followed by an increase in precipitation, peaking ~8,060 cal yr BP, and then decreasing. Drying conditions ensued after ~4,800 cal yr BP, and from ~1,700 cal yr BP to modern. Regional studies suggest mid-Holocene Epoch warming; some also indicate increased precipitation during those periods. A study at nearby Little Lyman Lake (Tingstad et al., 2011) displays a plankton percent record similar to the wetness record of the study fen. The fen core record does not indicate wet conditions at its base as expected. The record begins ~11,000 cal yr BP and likely represents an incomplete history of this Holocene fen, as the base of the wetland deposits was not reached.
13

How does groundwater subsidy of vegetation change as a function of landscape position and soil profile characteristics at the Ciha Fen (Johnson County, IA, USA)?

Even, Matthew James 01 May 2014 (has links)
No description available.
14

Effect of drainage and restoration on the ecology of peatlands in the Šumava Mountains / Effect of drainage and restoration on the ecology of peatlands in the Šumava Mountains

URBANOVÁ, Zuzana January 2012 (has links)
The effect of drainage and restoration on the ecology of different types of peatlands in the Šumava Mountains was investigated. The study was focused primarily on peat properties, vegetation dynamics, carbon gas fluxes and their linkages under the affected hydrological regimes.
15

Vliv managementu na vybrané druhy mechů rašelinných luk (Breidleria pratensis, Sphagnum warnstorfii, Tomentypnum nitens) / Effect of management on three moss species of fen meadows (Breidleria pratensis, Sphagnum warnstorfii, Tomentypnum nitens)

VELEHRADSKÁ, Tereza January 2013 (has links)
Effects of different types of management (control, mown, mown + disturbed (gaps) + litter removed) on three moss species of fen meadows were studied. Experimental plots were established at sixteen sites in the Bohemian Forest, in the foothills of the Bohemian Forest and in Českomoravská vrchovina. Relevés and micromaps of bryophytes in the plots 0.5 × 0.5m were sampled at the beginning of the experiment during the summer season of 2010 and then after 3 seasons (during the summer season of 2012) of performing management. The age of the abandoned meadows was also determined and values of pH, conductivity and height of water level of each plot were measured. Positive influences of both types of management on the cover of Tomentypnum nitens and of management with creating gaps and remowing of litter on the cover of Breidleria pratensis were significant. Effect of management on the Sphagnum warnstorfii was significant only when processes of remaining on already occupied places and the expansion to new places were tested separately. Enviromental values did not significantly influence the change of cover of any species between 2010 and 2012. In conclusion, it is clear that diverse management with reasonable use of these practices (mowing, creation of gaps, litter removal) is desirable for maintaining of vital and diverse bryophyte layer.
16

A floristic and phytogeographical analysis of the fen element at the Resthaven Wildlife Area (Castalia Prairie), Erie County, Ohio

Foos, Karen Adams January 1971 (has links)
No description available.
17

Taiwan shui ni gong ye zu zhi zhi mu liao zhi zhang yan jiu

Liang, Chengjin. January 1900 (has links)
Thesis (M.A.)--Guo li Zheng zhi da xue. / Cover title. Mimeo, copy. Includes bibliographical references.
18

Taiwan shui ni gong ye zu zhi zhi mu liao zhi zhang yan jiu

Liang, Chengjin. January 1900 (has links)
Thesis (M.A.)-- Guo li Zheng zhi da xue. / Cover title. Mimeo, copy. Includes bibliography.
19

Geomorphic and Geochemical Characteristics of Five Alpine Fens in the San Juan Mountains, Colorado

McClenning, Bree Kathleen 1985- 14 March 2013 (has links)
Fens are abundant in the San Juan Mountains. By exploring the geomorphology and geochemistry of fen wetlands, the functions that fens serve can be better understood. In this research, two main studies were conducted involving the geomorphology and geochemistry of fens. The first study involved a complex investigation of the geomorphology of five fen sites in the San Juan Mountains near Silverton, Colorado. Geomorphic maps were constructed for each fen site at a scale of ~1:3,000. A geomorphic classification scheme was then made based on fen location, and fens were placed in one of three categories: 1) valley-bottom, 2) valley-side, and 3) terrace. Fen circularity and elongation values were calculated for thirty fens to determine morphometry. A pattern for elongation of fens emerged between the three types of alpine fens with valley-bottom fens having an average elongation value of 1.7, valley-side 2.4, and terrace 1.9. Valley-side fens are more elongated than valley-bottom and terrace fens, which exhibit similar elongation values. In addition, sediment samples at each site were sectioned along visual breaks in the sediment column and were sieved. Mean phi values were calculated for each section and at each site. The mean phi values at California Gulch, Glacial Lake Ironton, Howardsville, Red Mountain Pass North, and Red Mountain Pass South, are 0.2112, 0.9045, 1.6028, 0.0178, and 1.0516, respectively. Overall, coarse-grained particles are associated with valley-side fens, and medium-grained particles are associated with valley-bottom and terrace fens. The second part of the study involved investigating the geochemistry of fen sediment. The geochemistry portion of this research focused on concentration and isotopic ratios of Pb and the amount of 137Cs in fen sediment to better understand variations of Pb with depth and calculate approximate sedimentation rates. Based on isotopic ratios of Pb, binary mixing was determined with the presence of ore mineralized Pb and non-ore mineralized. Binary mixing of two types of ore-mineralized Pb is present at the Howardsville fen and both ore-mineralized and non-ore mineralized Pb is present at the Red Mountain Pass North fen. Based on 137Cs in fen sediment at Howardsville, an average rate of deposition of sediment is approximately 0.16 cm/yr, with a visible change in sedimentation rates pre- and post-1960s.
20

Valuing archaeology : exploring the reality of the heritage management of England's wetlands

Fletcher, William January 2011 (has links)
This work primarily examines the management of wet-preserved archaeological sites in England, through an exploration of value and analysis of current management approaches. The aim is to explore whether the current policy frameworks, in particular the role of preservation in situ, can provide a sustainable future for wet-preserved archaeological sites. This work further seeks to conceptualise the modelling of sustainability, preservation and management decision making in wetland archaeological sites. Looking at the last 40 year of wetland research through the work of the large-scale wetland survey projects, this work initially considers the current understanding of wet archaeological sites in England. It also examines aspects of heritage management through the legislative and policy frameworks and their legacy. This work considers the implications that legislative and policy positions have for the management of wetland archaeological sites and examines the theoretical concepts that underpin them. This includes exploring reflective management, the development of research frameworks, and scoring mechanisms for the designation of sites. It also looks at broader constructs of value through the concepts of cultural and economic values. Three existing archaeological sites, a ringwork at Borough Fen near Peterborough, a marsh fort at Sutton Common near Doncaster and a triple post-alignment near Beccles, will be presented as case studies. These sites serve as examples of how the management of sites has been approached. The results of the case study analysis are used to develop a series of conceptual models looking firstly at sustainability and preservation in situ, and, secondly at preservation, value and decision making. The study concludes that the presumption in favour of preservation in situ can be challenging for wet preserved archaeological sites. Deterioration of the preservation environment can in some cases produce a similar decline in significance. Preservation in situ may therefore not be the most appropriate option for archaeological sites in wetlands.

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