Modelling of pH and inorganic aluminium after termination of liming in 3 000 Swedish lakes
(English)Manuscript (preprint) (Other academic)
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.
Acidification, surface water, geochemical equilibrium model, pH, Ali, Visual MINTEQ
IdentifiersURN: urn:nbn:se:kth:diva-94537OAI: oai:DiVA.org:kth-94537DiVA: diva2:525936
QS 20122012-05-112012-05-092012-05-11Bibliographically approved