No description available.

No description available.

This thesis describes a study of the distribution and geochemical behaviour of 137Cs, 241Am and 239+24P0u within the floodplain deposits of south west Scotland. These sediments have been contaminated with low level effluent discharged from BNFL's reprocessing plant at Sellafield on the Cumbrian coast. The study establishes that the dominant supply mechanism of anthropogenic radionuclides to the floodplain is via on-shore transfer of contaminated particulate material which has been mathematically modelled. A series of lateral transects across the floodplain has confirmed previous observations of highest concentrations furthest inland, illustrating the relationship between particle size and radionuclide concentration. The inventories observed for 137Cs were of the order of - 106 to 10' Bq m-2 and were somewhat higher than previously published data. The vertical distribution of radionuclides was investigated at Southwick merse and indicated a declining depth of occurrence of maximum radionuclide concentrations with distance inland. The observations from a series of transects, using a variety of sample collection methods permitted the construction of a schematic model of the merse. This model identified three distinct zones within the floodplain and enabled estimation of the total inventory for the coastline of south west Scotland. By these estimates less than 1% of the total environmental inventory of 137Cs discharged from Sellafield has been returned on-shore. Speciation studies on the availability of 13C7 s and 239+240Puin dicate that '37Cs is strongly retained within the residual phase of the sediment and that 239" 240Pu exhibits slightly enhanced availability, being associated with the organics and secondary Fe/Mn mineral phases. Evidence suggests that despite the increased environmental availability of 239+240Pu, both these radionuclides and 131Cs are not generally in a form which is available for plant uptake. Flow desorption studies have indicated that 137Cs is tightly bound to the sediment particles producing a Kp of -105 Ikg-1.

No description available.

No description available.

No description available.

No description available.

In spite of the widely perceived importance of suspended particulate material (SPM) , its distribution in the shelf seas and the processes controlling its variation are little known. This thesis reports an exploratory study of the spatial and time dependant variability of SPM in an area of the northern Irish Sea. SPM was determined both directly by gravimetric methods and via measurements of beam attenuation (c). Spatial distributions were determined from grid surveys using a profiling transmissometer. In addition a six month record of beam attenuation and current velocity was obtained from a site off the north coast of Anglesey. A clear spatial pattern in the surface distribution of c was observed which was similar to the distribution of h/ta, suggesting that concentrations of SPM are determined by the availability of TKE from tidal stirring. A strong seasonal cycle of c was observed in mixed water, with values decreasing in June, July and August which suggested a reduction in the supply of SPM during summer. In stratified water, high concentrations of SPM remained confined to the dense layer below the thermocline. The seasonal cycle was observed in the time series from the mooring, but in addition there was a marked response to tidal currents in the spring and in autumn. Close analysis of the record in April and May-showed signals at M% and M4frequencies. These variations in c were attributed to a local response to tidal currents causing erosion of the sea-bed and to the oscillation of a horizontal gradient in c in the region. A regression model was found to explain 35% of the variance in data from a5 week time series. 70% of the variance was explained for four day time series, near spring tides. The relationship between c and tidal flows was more marked at spring tides than at neaps.

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Key processes affecting the transport of particulate trace metals in the coastal waters of the Irish and North Seas have been examined. Sample collection and experimentation was carried out on board R.R-S. Challenger in January 1992 (Irish Sea) and in December 1992 and November 1993 (North Sea). Particulate samples were digested in IM HCI and the concentrations of Ca, Cd, Co, Cu, Fe, Mn, Pb and Zn were determined, together with the 206/207Pb isotopic ratio. In the North Eastern Irish Sea the concentrations of suspended particulate trace metals were affected significantly by tidal processes, such that ebb tides transport particles of higher trace metal concentrations from the nearshore, while flood tides transport metal-depleted particles from offshore. This tidally-induced transport was confirmed by complementary 206/207Pb analyses, which showed the value of this technique in particle tracing. In the North Sea suspended particulate trace metal concentrations were higher adjacent to industrialised estuaries and high Pb concentrations were found m the Tyne/Tees region (in the range 200 - 340 ug g-1), in combination with low 206/207Pb suggesting an anthropogenic origin. Estimated fluxes of trace metals from the Humber Estuary to the North Sea were relatively small compared to the PARCOM inputs to the estuary. There was little evidence of interannual variability in these fluxes compared to those obtained in December 1988. Samples of end-members of the Humber Plume particle mixing series (estuary and cliffs) were used in radiochemical uptake studies, which indicated a response time of about 1 day for 109Cd, 137Cs and 65Zn to reach a new equihbrium. When the end-members were mixed together in various proportions they showed the uptake of 109Cd and 54Mn behaved non-additively. Settling of suspended particulate trace metals in the plume region was examined in unique experiments involving stable and radioisotopes. It was shown that trace metals were preferentially associated with different settling fractions. Lead was associated with slow settling particles whereas Cu was associated with particles settling more rapidly. The results presented in this dissertation allowed the development of a conceptual model for fine sediment transport for trace metals, which could be interfaced with established hydrodynamic models.