The solubility of aluminum in acidic forest soils: Long-term changes due to acid deposition

Journal Article · Sat Jan 01 04:00:00 EST 1994 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(94)90448-0· OSTI ID:5217883

Mulder, J; Stein, A ^[1]

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1. Wageningen Agricultural Univ., Wageningen (Netherlands)

Despite the ecological and pedogenic importance of Al, its solubility control in acidic forest soils is poorly understood. Here the authors discuss the solubility of Al and its development with time in three acid brown forest soils in The Netherlands, which are under extreme acidification from atmospheric deposition. All soil solutions (to a 60 cm depth) were undersaturated with respect to synthetic gibbsite (Al(OH)[sub 3]; log K = 9.12 at 8[degrees]C), with the highest degree of undersaturation occurring in the surface soil. In about one third of the individual soil layers a significant positive correlation existed between the activity of Al[sup 3+] and H[sup +], but this relationship was far less than cubic. Kinetically constrained dissolution of Al is unlikely to explain the disequilibrium with respect to gibbsite, because undersaturation was highest through summer when water residence times were longest and temperatures greatest. Time series analysis of six year data set for several soil layers revealed a significant annual decline in soil solution pH and Al solubility (defined as log Al + 3 pH) despite a constant concentration of strong acid anions. The annual decline of both pH and Al solubility was greatest in the surface soil and was positively correlated with the relative depletion of reactive organically bound soil Al. The results support the earlier hypothesis that in strongly acidified forest soils complexation by solid phase organics controls the solubility of Al, even in mineral soil layers relatively low in organic C. The data lend no support to the current widespread, and often uncritical, use of gibbsite as a model for the Al solubility in highly acidic forest soils (pH < 4.5) of the temperate zone.

• OSTI ID: 5217883
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 58:1; ISSN GCACAK; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
540220* -- Environment
Terrestrial-- Chemicals Monitoring &amp; Transport-- (1990-)
ACIDIFICATION
ALUMINIUM
ELEMENTS
FORESTS
METALS
PH VALUE
SOILS
SOLUBILITY