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| Matschonat, G; Vogt, R: Significance of the total cation concentration in acid forest soils for the solution composition and the saturation of exchange sites, Geoderma, 84, 289-307 (1998) | |
Abstract:
To assess the ecological quality of acid forest soils, the base saturation and the solution pH, Al
concentration and base cationrAl ratios are of interest. Relationships between these parameters
would facilitate this assessment. Examples are empirical relationships between pH and base
saturation, and between the Al concentration and the ionic strength of the soil solution. From a
mechanistic point of view, the theory of cation exchange implies that the total cation concentration
SCCssum of cationic charge in solution.is a key factor in soil–solution interactions. Our aim
was to demonstrate that relationships with the SCC to be expected from the theory can be
observed in the field. Such relationships have special relevance in view of a decrease in acid
deposition in Europe, which will lower the SCC. We studied the effects of the SCC on the soil
solution composition and the saturation of exchange sites in simulated batch experiments based on
the Gaines and Thomas equation. The results were compared to field data from a range of soils
under the influence of highEurope.and negligibleNew Zealand.atmospheric deposition.
Equilibrium calculations predict an increase in the fraction of trivalent cations in solution with
SCC, while the fraction of monovalent cations decreases. This pattern with SCC was observed in
part of the lysimeters on a site with high deposition rates. The variation in SCC among soil
solutions from New Zealand also produced the pattern, whereas this was not the case for a broad
range of European soils. We hypothesize that this difference be due to the impact of acid
deposition on the European soils. The most pronounced expression of the pattern was observed for
lysimeter solutions from a European experimental siteSolling.under ‘clean rain’ treatment,
where a large variation in SCC occurred. To estimate the development of base saturation in the
European soils under conditions of decreasing deposition, we calculated exchange equilibria for
European soils on the basis of soil solutions from New Zealand. The results indicated that an
increase in base saturation is not to be expected, as a low total cation concentration tends to lower the base saturation. We concluded that the SCC carries important information on the composition
of the soil solution and probably also on the saturation of exchange sites. The patterns created by
cation exchange can be observed in natural soil solutions on different spatial scales. q1998
Elsevier Science B.V. All rights reserved.
Keywords: acid deposition; aluminium; cation exchange; forest soils; ionic strength; soil solution |
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