Suspended sediments were collected from 3 rivers, the Rheidol, Ystwyth and Tywi on a regular basis. The sediment samples were studied for a number of physical and chemical properties to identify characteristics which might distinguish between source areas. These properties included mineralogy, magnetic properties, sediment colour, and the trace element composition of .sediments. Point-sources for heavy metals can be identified for all three catchments, and the metal content, and partitioning was studied. The metal content, and the site on the sediment to which the metal is bound has been found to vary with discharge. The response to discharge is not the same for all metals, but in general, at peak discharge the lead was in the Fe/Mn oxide and organic fractions, and these fractions became important for cadmium. Prior to the flood peak however, up to 70% of the cadmium was in easily exchangeable form. The organic fraction was the most important for copper throughout the flood. j Sediments which had been deposited in floodplain features and in lakes were also studied, as they recorded the pattern of sediment transport during floods over an extended period. In the Ystwyth catchment the metal content and ratios between metals was used to determine the importance of two mining areas for the supply of sediment to a floodplain during the mining period (1860-1890). Sediments from profiles in fossil alluvial channels on a floodplain in the Rheidol showed a dramatic increase in metal .concentrations in the mid-profile, and recorded the period of concerted mining in the catchment. Mining operations in the Ystwyth catchment caused widespread lateral aggradation of floodplains, as established at Trawscoed. The historic record of catchment changes as contained in the sedimentary profile of reservoirs in the Mendips was studied. The record in Blagdon and Chew Valley lakes in the Mendips was deciphered using a combination of sedimentological, magnetic and chemical data. A catastrophic flood which is documented for the area, which occurred in July 1968, caused the mobilisation and transportation of sediments from dry valleys in the catchment. Sediments deposited during the floods were distinguished by their coarse nature, by an increase in magnetic susceptibility and the parameter'S', which indicated a topsoil source, and by a change in the partitioning of lead and zinc, where the organic fraction was absent.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:380634 |
| Date | January 1984 |
| Creators | Bradley, S. B. |
| Publisher | Aberystwyth University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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