Journal of Conference Abstracts

Evidence of Current Soil Acidification in Spruce Stands (Strengbach Catchment, Vosges Mountains,
Northeastern France)

Etienne Dambrine¹ (dambrine@nancy.inra.fr), Benoît Pollier¹, Anne Poszwa¹,
Michelene Colin Belgrande¹, Anne Probst² (aprobst@illite.u-strasbg.fr),
Daniel Viville³ (daniel@equinoxe.u-strasbg.fr), Philippe Biron³ &
André Granier⁴ (agranier@nancy.inra.fr)

¹ INRA, Unité Cycles Biogéochimiques, 54280, France.

² CNRS, Centre de la Géochinie de la Surface (CGS)l 1 rue Blessig, 67084 Strasbourg, France.

³ CELEP-URP, 3 rue de l'Argonne, 67083 Strasbourg, France.

⁴ INRA, Unité Ecophysiologie, 54280 Seichamps, France.

To demonstrate ongoing soil acidification under spruce stands at Aubure (Strengbach Catchment, Northeastern France), soils from two adjacent spruce stands aged 35 and 90 years, were sampled intensively in 1990 and resampled in 1996. Although soils already were extremely acidic in 1990, the comparison showed a strongly and highly significant decrease in Ca and Mg saturation of the fine earth soil fraction at all depths in the two sites except in the 0-10 cm layer in which base saturation remained constant. Annual loss rates of base cations was calculated and compared to the results of input-output budgets calculated for 10 years at the same sites. In addition, weathering rates for base cations were modeled using the geochemical model PROFILE and a detailed mineralogical investigation of the soil profiles. Losses of Ca calculated from the budgets are similar to losses of Ca estimated from changes in exchangeable Ca stores. Ca appears to be lost at a rate of approximately 7 kg ha^-1 yr^-1. Because the total stores of exchangeable Ca in the fine earth soil fraction is less than 100 kg ha^-1, this rate of loss is extremely high and endangers the future fertility of the site. Comparatively, the loss of Mg on the exchange complex was higher than that computed from the field budget. Various reasons, including most probably uncertainties linked to the extremely low levels of Mg in the ecosystem, may explain this discrepancy. Since 1987, a general decrease in the (Ca + Mg)/Al ratio in soil solution was observed at both sites. This trend was not the result of variation in the concentrations of mineral anions during the study period. This study demonstrates the rapid acidification of soils poor in weatherable minerals in the Vosges Mountains under the influence of present-day acid deposition levels and management practices in spruce stands. In contrast, beech mineral budgets in adjacent beech stands appear to be nearly balanced.