Quantifying current and preindustrial occurrence of inorganic
aluminium in Swedish surface waters
S. J. KÖHLER1 , M. ERLANDSSON1, J. FÖLSTER1, H. , K. BISHOP1,2, S. LÖFGREN1
1
Department of Aquatic and Environmental Sciences, Swedish University of Agricultural Sciences (SLU), Box
7050, 75007, Uppsala, Sweden
2
Department of Earth Sciences, Uppsala University, Villavägen 16, 75236, Uppsala, Sweden
Keywords: alumininum, organic acidity, acidification assessments
The occurrence of elevated concentrations of
inorganic aluminum (Ali) in surface waters is
critical for evaluating current acidity status and
liming operations in Sweden as concentrations of
above 30 ppb may affect certain fish species.
A combined statistical and hydrochemical analysis
of a large number of acid sensitive lakes all over
Sweden was used to quantify the occurrence of Ali
and to estimate projected changes of Ali in those
surface waters.
It is possible to arbitrarily separate lakes with high
(> 50ppb Ali but not >25 ppb) using ANC and
strong organic acid anions as proposed by
Lawrence et al. (2010). For this we slightly adapted
an earlier version of the strong organic acid
approach presented by Köhler et al. (2001) to
identify a breakpoint from which on Ali is below 50
ppb. We then tested whether MAGIC predicted
changes in pH would allow distinguishing those
lakes from the remaining data set. A calculated
delta pH of 0.4 pH, that is currently used an
assessment criterion for acidified lakes, is not
sufficient to identify these lakes. Instead 50% of
lakes with a calculated delta pH > 0.4 still had Ali
below 50ppb. The occurrence of naturally high
concentrations of inorganic aluminum is driven by
the presence of organic acids, fluoride and pH and
any changes in any of those parameters over time
will affect the determination of natural background
levels. Concentrations of at least 25 ppb have to be
regarded as natural in large areas of a landscape
that is mostly covered by weakly buffered soils
draining organic rich waters.
An empirical set of equations for calculating the
occurrence of Ali from pH, TOC and fluoride
explained more than 90% of the observed variation
in Ali. This model together with the projected
changes in pH at those sites using the Swedish
MAGIC library were used to quantify the potential
changes in Ali between 1860 and 2010. Changes in
pH of at least 1 pH unit were necessary to augment
the presence of inorganic aluminum by more than
25ppb. i.e a doubling of the concentration from a
natural background.
Only a combined use of MAGIC predicted pH and
the strong acid anion concept can identify lakes
with Ali above 25ppb. Predicted changes in pH and
Ali in the MAGIC code are very sensitive to the
organic acid model. Predicted changes of Ali over
time have therefore to be considered very carefully
and were possible they should be verified with
other approaches.
References
Köhler, S. Löfgren, S., Wilander, A., Bishop, K. (2001) A simple tool to predict and analyze organic acid anion
charge in low ionic strength surface waters. Water, Air and Soil Pollution 130, 1-4: 799-2804.
Lawrence, G. B.; Sutherland, J. W.; Boylen, C. W.; Nierzwicki-Bauer, S. W.; Momen, B.; Baldigo, B. P.;
Simonin, H. A. (2007) Acid rain effects on aluminum mobilization clarified by inclusion of strong organic acids.
Environ. Sci. Technol., 41 (1), 93–98, DOI:10.1021/es061437v.
Sjöstedt, C. S., Gustafsson, J. P.; Köhler, S. J. (2010) Chemical Equilibrium Modeling of Organic Acids, pH,
Aluminum, and Iron in Swedish Surface Waters. Environmental Science & Technology, 44, (22), 8587-8593.