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Colloidal geochemistry of speleothem-forming groundwaters

Hartland, Adam (2011)
Ph.D. thesis, University of Birmingham.

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Abstract

Natural aquatic colloids (solids with dimensions between 1 nm and 1 micron) were studied in cave waters that feed secondary carbonates [speleothems]. Results show that during hydrologically quiescent periods, trace metal (Tr) binding (e.g. Cu, Ni, Co) is dominated by humic-like, natural organic matter (NOM), with the smallest NOM-Tr complexes (≤1 to ca. 4 nm diameter) being the least labile at high pH (>pH 10). Partitioning of NOM:Tr between solution and crystal occurs minimally for the strongest complexes, providing a measure of NOM adsorption. Rapid fluxes of coarse (>100 nm) soil organic matter (SOM) and Tr in dripwaters often follow peak infiltration events, the coarse fraction of NOM quenching fluorescence in finer fractions (<100 nm). Termed ‘high-flux’ (HF), this mode of NOM-metal transport contrasts with the humic-like or ‘low-flux’ (LF) mode both hydrologically and chemically, resulting in shifts in trace metal ratios (e.g. Cu:Ni) which are characteristic of changes in the competitive binding of metals for suitable sites in NOM, and diagnostic of qualitative shifts in NOM composition (i.e. relatively more aromatic/hydrophobic). This process becomes manifest in speleothems, resulting in high- and low-flux trace metal end-members and providing information on NOM aromaticity. Changes in HF:LF metal ratios in speleothems are linked to processes in soils which are ultimately mediated by climate (i.e. ambient temperature and infiltrating precipitation); they may provide information on infiltrating precipitation, on the occurrence of surface disturbances (e.g. deforestation) and NOM composition. HF:LF indices complement the existing array of speleothem climate proxies, but each specific system and setting must be understood to ensure their proper interpretation.

Type of Work:Ph.D. thesis.
Supervisor(s):Fairchild, Ian and Lead, Jamie
School/Faculty:Colleges (2008 onwards) > College of Life & Environmental Sciences
Department:School of Geography, Earth and Environmental Sciences
Keywords:Colloids; trace metals; stalagmites; palaeoclimate
Subjects:QE Geology
GE Environmental Sciences
QD Chemistry
Institution:University of Birmingham
ID Code:1659
Refereed:YES
This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder.
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