Deacidification effect of the litter layer on forest soil
during snowmelt runoff––laboratory experiment and
its basic formularization for simulation modeling
Department of Basic Science and Environment, ESAC––Polytechnic Institute of Coimbra, Bencanta, 3040-316 Coimbra, Portugal
Received 6 January 2003; received in revised form 26 September 2003; accepted 12 October 2003
The forest soil ecosystem can buffer and neutralize acidic airborne pollutants to some extent, but extensive acidi-
fication degrades the soil ecosystem. Several investigations have shown that surface flows often show particularly low
pH values in rivers and lakes during snowmelt and that this acidification phenomenon takes place in a short time frame.
Acid water from snowmelt first makes contact with the litter layer in the soil ecosystem. Therefore, a laboratory
experiment was performed to study the impact of forest litter on the chemical composition of the water solution. The
experiment presented in this paper confirmed that deacidification with a little leachate of organic matter is caused by
cation exchange not only in upper mineral soil but also in the litter layer and that leachate of labile Al is restrained in
the presence of litter. An attempt was made to incorporate these factors into the biogeochemical module of the model
(ILWAS) to accurately estimate damage by acidification.
? 2003 Elsevier Ltd. All rights reserved.
Keywords: Acidic pollution; Biogeochemical module; Humus soil; Leachate; Meltwater
Emissions of sulfuric and nitrogenous pollutants such
as SO2and NOxare the main causes of airborne acidi-
fication. These pollutants subsequently reach the ground
and overlying vegetation in rain and snow (Thunberg
and Hanneberg, 1993). Soil acidification may have bio-
logical effects in three respects (Thunberg and Hanne-
berg, 1993): through lowering of the pH value (namely,
increasing Hþconcentration); through an increase in the
level of labile aluminum (mainly free Al3þ) and other
toxic metals in the soil water; and through a loss of plant
nutrients such as potassium, calcium and magnesium
due to increased leaching. If a forest ceases to be nor-
mally productive, logging has to be cut back, jobs are
lost and national economies deteriorate, at the same
time as a key resource for industry diminishes. From the
economic and environmental viewpoints, it is important
to estimate soil and forest damage caused by acidifica-
tion and to take proper countermeasures.
Several investigations (Davies et al., 1982; Brimble-
combe et al., 1985) have shown that rivers and lakes
often show particularly low pH values during snowmelt
and that this acidification phenomenon takes place in a
short time frame. Acid water from snowmelt first makes
contact with the forest litter layer when it reaches the
soil. Therefore, the main purpose of this paper is to
investigate the effect of forest litter on the daily variation
of the ion concentrations in snowmelt water.
2. Acidic solute in snowmelt runoff
It is found that the first fractions of snowmelt water
contain higher amounts of ions than the bulk snow
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0045-6535/$ - see front matter ? 2003 Elsevier Ltd. All rights reserved.
Chemosphere 54 (2004) 1163–1169
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