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Title: The vertical distribution, associations and mobility of Pb and other elements in an ombrotrophic peat bog
Author: Freeman, Alex
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2001
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From the results of this study, elevated Pb concentrations of up to 350 mg/kg(dry weight) were found mainly in the top 0-30 cm of the solid phase peat. This was consistent with the deposition of anthropogenic Pb particularly since the onset of the Industrial Revolution. Peak concentrations of 328 and 165 mg/kg were found at 4-6 cm and 20-22 cm respectively. Porewater Pb concentratiom were typically very low with a maximum value of ~0.04 mg/l and values <0.01 mg/l below 30 cm. The two peaks in porewater Pb were coincident with those in the solid phase peat and the porewater/solid phase ratio of Pb concentrations did not vary over significantly over these top sections. From this information alone, it appeared that there was a simple equilibrium distribution of Pb between the solid and aqueous phase and that very little of the total Pb was present in the porewater. The peak at 20-22 cm in both the solid phase and the porewater did, however, coincide with the maximum in porewater organic carbon concentration. Determination of the proportion of Pb in humic extracts showed, however, that very little of the total Pb was associated with humic materials at this depth. In addition, from the distributions and humic-associations of other elements, processes including active plant uptake of nutrients (Mn, Na, K, Ca), reductive dissolution (Fe) and mineral dissolution (Al, Ti) did not affect the vertical distribution of Pb within the peat. Finally, there was good agreement between the 206Pb/207Pb isotope ratios obtained for the solid phase peat, the porewater and each of the humic extracts, particularly in the uppermost sections of the core where the isotope signature changes from 1.136 to 1.177 in the solid phase, from 1.143 to 1.179 in the porewater and, for example, 1.143 to 1.180 in the humic acid extract. The similarity of the isotopic profiles provides further evidence to support the post-depositional vertical immobility of Pb in ombrotrophic peat bogs. Overall this work has provided a dated concentration profile for Pb which can be used as a historical record of environmental Pb contamination. It has also extended the understanding of biogeochemical processes occurring in peat bogs although these do not influence the vertical concentration profile of Pb. In particular, the use of stable Pb isotopes established that even humic complexation after deposition was unlikely to affect the vertical distribution of Pb.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available