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Aluminium speciation in streams and lakes of the UK Acid Waters Monitoring Network, modelled with WHAM

Tipping, Edward; Carter, Heather. 2011 Aluminium speciation in streams and lakes of the UK Acid Waters Monitoring Network, modelled with WHAM. Science of the Total Environment, 409 (8). 1550-1558. 10.1016/j.scitotenv.2010.12.030

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Abstract/Summary

The Windermere Humic Aqueous Model (WHAM) incorporating Humic Ion-Binding Model VI was applied to analytical data from the United Kingdom Acid Waters Monitoring Network, collected for 22 streams and lakes over the period 1988-2007, to calculate the chemical speciation of monomeric aluminium (Almon) in 3087 water samples. Model outputs were compared with analytical measurements of labile and non-labile Almon concentrations, the former being equated with inorganic forms of Almon and the latter with organically-complexed metal. Raw analytical data were used, and also data produced by applying a correction for the possible dissociation of organically-complexed Almon, and therefore its underestimation, during passage through the analytical cation-exchange column. Model calibration was performed by finding the conversion factor, FFADOC, between the concentration of isolated fulvic acid, with default ion-binding properties, required by the model, and the measured concentration of dissolved organic carbon, [DOC]. For both uncorrected and corrected data, the value of FFADOC for streams was greater than for lakes, indicating greater binding activity towards aluminium. Model fits were better using uncorrected analytical data, but the values of FFADOC obtained from corrected data agreed more closely with previous estimates. The model provided reasonably good explanations of differences in aluminium speciation between sampling sites, and of temporal variations at individual sites. With total monomeric concentration as input, WHAM calculations might substitute for analytical speciation measurements, or aid analytical quality control. Calculated Al3+ activities, aAl3+ showed a pH-dependence similar to that previously found for other surface waters, and the modelling exercise identified differences between waters of up to two orders of magnitude in the value of aAl3+ at a given pH. The model gives the net charge of dissolved organic matter, which is calculated to have risen significantly at 15 of the AWMN sites, due to increases in pH and decreases in aluminium concentration.

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1016/j.scitotenv.2010.12.030
Programmes: CEH Topics & Objectives 2009 onwards > Biogeochemistry > BGC Topic 2 - Biogeochemistry and Climate System Processes > BGC - 2.1 - Quantify & model processes that control the emission, fate and bioavailability of pollutants
CEH Sections: Shore
ISSN: 0048-9697
Additional Keywords: acidification, aluminium, chemical speciation, dissolved organic carbon, modelling, surface waters
NORA Subject Terms: Ecology and Environment
Chemistry
Date made live: 14 Mar 2011 16:00
URI: http://nora.nerc.ac.uk/id/eprint/13610

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