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No description available.

This thesis examines the extent to which geomorphological change in sub-arctic landscapes may be driven by rapid declines in population over timescales of decades to centuries. Demographic decline driven by disease in pastoral agricultural systems is expected to alter patterns of land use. Using a chronology with 20 visible dated tephra layers from AD 870 to present, 2625 tephra layers were identified in 200 sediment profiles. Rates of sediment accumulation dated by tephra provide a record of erosion in Skaftártunga, South Iceland. The scale of enquiry is that of individual landholdings (5–10 km2) over decades to centuries; in order to tackle questions of resilience and change within coupled socio-ecological systems larger and smaller spatial scales (regions of 400 km2 and individual sediment profiles) and longer and shorter temporal scales (2.6 ka and years to decades) are also considered. The novel application of photogrammetric techniques to recording stratigraphic sections increases the frequency of measurement from tens to hundreds per stratigraphic unit and the resolution from ±2.5 mm to ±1 mm. This technique improves the accuracy of representative measures of sediment accumulation and their use in measuring landscape change. Two little known 15th century AD Grímsvötn tephras are mapped and dated to AD 1432±5 and AD 1457± 5 using sediment accumulation rates. A period of landscape stability from AD 1389–1597 is consistent with reduced grazing pressure due to population declines of more than 30% after plague in AD 1402–1404 and AD 1494. Climatic deterioration from AD 1450-1500 does not increase erosion as much as expected; this may be due to decreased grazing pressure after population decline in the 15th century. Increased erosion from AD 935–1262 is related to woodland clearance and increases in sediment accumulation post AD 1625 are related to climatic cooling during the Little Ice age and the migration of erosion fronts into deep lowland sediments.

This thesis reports an investigation of soil erosion problems associated with maize cultivation in England. To place the investigation into a broader context, the study commences with a review of soil erosion problems more generally, before focusing on the specific on-site and off-site problems associated with maize cultivation. Agricultural statistics are used to quantify the recent expansion of maize cultivation in England and attention is directed to both the temporal trends and spatial patterns involved. A major expansion of maize cultivation occurred in England between 1990 and 2000. Particular attention is then directed to the expansion of maize cultivation in Southwest England, since this is a very important area for cultivation of forage maize. Against this general background, a more detailed investigation of soil erosion associated with maize fields and its impact on the local streams and rivers was undertaken. This focused on two river catchments, namely the River Culm above Cullompton, Devon, and the River Tone above Taunton, Somerset. These two basins were selected as having a high density of maize fields within their catchments. A detailed field survey was undertaken to identify all the fields used for maize cultivation in the two catchments during 2004 and the previous two years and to provide a map of their location. More detailed work, aimed at quantifying both gross and net rates of soil loss, was undertaken on six fields selected to be representative of maize fields in the two catchments. Beryllium-7 measurements were used to estimate the erosion associated with a period of heavy rainfall in late December 2004 and early January 2005, when the harvest fields were left in a bare compacted conditions, with little or no vegetation cover and field observations indicated that significant erosion occurred. The results obtained from the beryllium-7 measurements which related only to the short period in late 2004 and early 2005 were complemented by caesium-137 measurements in the same fields which were used to obtain an estimate of the longer-term (i.e. ca. 45 years) mean annual erosion rates associated with the more traditional land use that had characterized these fields prior to the introduction of forage maize cultivation. These results indicated that the introduction of maize cultivation increased gross and net rates of soil loss by ca. 4 and 8 times, respectively and significantly increased sediment delivery ratios, resulting in more efficient delivery of sediment from the eroding fields to the streams. An assessment of the likely impact of sediment mobilised from the maize fields within the catchments of the River Culm and River Tone during winter 2004-5 was made by establishing a sediment monitoring and sampling programme at the downstream gauging stations on these two rivers over the period November 2004 to March 2005. Estimates of the suspended sediment loads of both rivers were obtained for this period and these were compared with an estimate of the total amount of sediment delivered to the water courses in the two catchments from maize fields based on an upscaling of the results obtained from the beryllium-7 measurements undertaken on the six representative fields. Uncertainties regarding both field to channel and within channel and floodplain conveyance losses precluded definitive comparison of the estimates of the amounts of sediment delivered to the water courses from maize fields with the measured sediment loads. However, the results obtained demonstrated the likely importance of the contribution from eroding maize fields to the suspended sediment loads of the Rivers Culm and Tone during winter 2004-5. The geochemical properties of suspended sediment collected from the two rivers were also compared with the equivalent properties of soil collected from the surface of maize fields within the two study catchments, in order to provide further evidence of the impact of maize cultivation on their suspended loads. The available geochemical data confirmed that much of the sediment transported by the Rivers Culm and Tone could have been mobilized from maize fields, but the lack of detailed geochemical data, precluded a definitive conclusion regarding its source. The results obtained from the field-based component of the study have been combined with the information on the regional and national patterns of maize cultivation and synthesized to provide a general assessment of the likely environmental impact of maize cultivation in England. This information has in turn been used to consider the potential for developing improved land management practises to reduce the environmental impact of maize cultivation within the context of the EU Common Agricultural Policy (CAP) and the Water Framework Directive (WFD). Finally, recommendations for the further development and extension of the study are provided.

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The Mfolozi, the second largest catchment in KwaZulu Natal, is already severely degraded over substantial areas. Its mean annual sediment load is extremely high and deposits on its floodplain have caused very serious financial losses. Previous studies in the catchment have attributed its soil loss to poor land use practices by peasant farmers. There is a concern that this production will be substantially increased by land use changes incumbent on the land reform programme. In order to ensure that this programme does not lead to increased degradation and exacerbate associated environmental and socio-economic problems, this study identified both subcatchments and land types that are highly susceptible to erosion and already highly eroded. An unpublished map showing the location of 19 categories of erosional forms and three categories of extreme relief features was available for use. The density (and areal extent in the case of badlands) of each of these forms within each of the 16 possible land types within each of the 43 subcatchments, was obtained and related to their dominant physiographic variables. The findings revealed that the catchment is not as severely or extensively eroded as suggested by previous studies. A substantial portion of the former Natal areas, mostly targeted for reallocation, have however, been shown to be unsuitable for this purpose. / Thesis (M.A.)-University of Durban-Westville, 1996.

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The potential of remote sensing in upland soil erosion studies has been examined on Glaisdale Moor, North Yorkshire Moors. The study considers four different remote sensing sources, viz. sequential air photographs, ground radiometry, Landsat Thematic Mapper (TM) and SPOT simulation. Sequential air photographs have been interpreted in order to elucidate the land use/land cover changes and the drainage development and associated erosion problems in the region. A series of statistical analyses were employed in an effort to establish the relationships between the different spectral variables and the soil/ground variables. Attempts have also been made to evaluate the spectral separability performance of the Ground radiometer, the Landsat TM and the SPOT simulation wave bands. The Landsat TM and the SPOT simulation imagery have been further analysed in order to gather information about the best band and band combinations that would be required to optimize the discrimination of moorland surface types including eroded areas. Digital image processing of the Landsat TM and the SPOT simulation subscene for Glaisdale Moor was performed using the DIAD image processing system. The land use/land cover classification information derived from the air photographs, the Landsat TM and the SPOT simulation, has been used as an input into a soil loss prediction model (USLE) to predict the soil erosion rate of the study area. Of the various remote sensing systems used, air photographs and TM data proved the most useful in this area.

No description available.

No description available.