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Modelling of pH and inorganic aluminium after termination of liming in 3 000 Swedish lakes
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Geochemistry and Ecotechnology.
Stockholms Universitet, ITM.
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Geochemistry and Ecotechnology.ORCID iD: 0000-0001-8771-7941
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Significant resources are spent on counteracting the effects of acidification, mainly by liming. Due to a lower sulphur and nitrogen deposition in Europe and North America, authorities are reducing liming, changing directives and strategies for remediation. However, as the acid-base buffer capacity differs in different water bodies, the desirable reduction of the lime dose is variable. In this study, a geochemical model is used to predict pH and inorganic monomeric aluminium (Ali) when liming reduced and finally terminated in the 3 000 Swedish lakes that have been subject to liming. The model used estimations of Ca and Mg concentrations not affected by liming based upon the Ca/Mg ratio in nearby unlimed reference lakes. For modelling of pH and inorganic aluminium we used the geochemical model program Visual MINTEQ including the Stockholm Humic Model recently calibrated for Swedish fresh water. The predictions were confirmed by results from six monitored lakes, in which liming had been terminated. The use of geochemical modelling proved to be a promising tool for the calculation of accurate lime requirements in acid waters. For simulations in which liming was completely terminated, the pH value decreased with, on average, 0.9 pH units to pH 5.9, whereas Ali increased with 18 μg L-1 to 31 μg L-1. If liming was reduced by half, the pH would drop only 0.3 pH units and Aliwould increase with 2 μg L-1. Lakes in the south-western part of Sweden were predicted to reach a lower pH and higher Ali, as could be expected due to their larger historical S deposition. The results indicate that liming can be terminated in certain areas and be reduced without large pH reductions in the fresh water.

Keyword [en]
Acidification, surface water, geochemical equilibrium model, pH, Ali, Visual MINTEQ
National Category
Geochemistry
Identifiers
URN: urn:nbn:se:kth:diva-94537OAI: oai:DiVA.org:kth-94537DiVA: diva2:525936
Note
QS 2012Available from: 2012-05-11 Created: 2012-05-09 Last updated: 2012-05-11Bibliographically approved
In thesis
1. Iron and aluminium speciation in Swedish freshwaters: Implications for geochemical modelling
Open this publication in new window or tab >>Iron and aluminium speciation in Swedish freshwaters: Implications for geochemical modelling
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Speciation governs transport and toxicity of trace metals and is important to monitor in natural waters. Geochemical models that predict speciation are valuable tools for monitoring. They can be used for risk assessments and future scenarios such as termination of liming. However, there are often large uncertainties concerning the speciation of iron and aluminium in the models, due to the complicated chemistry of these metals. Both are important in governing the speciation of other metals, due to (i) their capacity to form minerals onto which metals can adsorb and (ii) their ability to compete for binding sites to natural organic matter (NOM). Aluminium is also potentially toxic and is therefore closely monitored in acidified freshwaters. In this study different phases of iron in Swedish lakes were characterised. This required a good method for preconcentrating the iron colloids. A new method was developed in this thesis that uses an anion-exchange column to isolate the iron colloids prior to characterisation with extended X-ray absorption fine structure (EXAFS) spectroscopy. Iron was present as ferrihydrite in particles but was also strongly monomerically complexed to NOM in two Swedish lakes. Based on the results an internally consistent process-based geochemical equilibrium model was presented for Swedish freshwaters. The model was validated for pH (= 9 400) and inorganic monomeric aluminium (Ali) (n = 3 400). The model could simulate pH and Ali simultaneously, and be used for scenario modelling. In this thesis, modelling scenarios for decreases and complete termination of liming are presented for the 3 000 limed Swedish lakes. The results suggest that liming can be terminated in 30 % of the Swedish lakes and decreased in many other lakes.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. xiv, 51 p.
Series
Trita-LWR. PHD, ISSN 1650-8602 ; 1065
Keyword
Geochemical equilibrium modelling, pH, adsorption to ferrihydrite, metal-NOM complexation, liming, EXAFS spectroscopy
National Category
Geochemistry
Identifiers
urn:nbn:se:kth:diva-94528 (URN)978-91-7501-373-2 (ISBN)
Public defence
2012-10-05, V1, Teknikringen 76 1 tr, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 2007-4468
Note

QC 20120919

Available from: 2012-05-11 Created: 2012-05-09 Last updated: 2012-09-19Bibliographically approved

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