ABSTRACT: Bilans elementaires holocenes et alteration des mineraux dans trois sols forestiers du Quebec meridional. [Elemental budgets for the Holocene and mineral weathering in three forest soils from southern Quebec].

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Abstract

We calculated elemental fluxes for the Holocene and historical weathering rates in three forested watersheds using the method proposed by Brimhall et al. (1991a, 1991b). Thesoils (Hermine:HER; Rouyne-1: RN1; Rouyne-4: RN4) were selected because they formed in contrasting parent materials and were exposed to different levels of trace metal deposition from the atmosphere. The strain value (ICV) calculated using Zr is positive (dilation) in RN1 and in the B horizons of HER. The strain is positively correlated to the organic C concentration and to the Al and Fe oxide contents. The analysis of soil profiles further allows the identification of three element groups. A first group (Ca, K, Mg, Mn, Na, Si) shows concentrations decreasing from the C horizon to the surface of the profile because of increasing mineral weathering. The second group (Al, Fe, P, Ti, Cr, Ni) is enriched in the B horizons while being depleted in the Ae. This mixed pattern reflects the combined effect of oxide formation (Al, Fe, Ti) and of elemental retention of these oxides (P, Cr, Ni). The third group (Cd, Cu, Pb, Zn) refers to elements presenting highly positive fluxes in the surface horizons in response to the atmospheric deposition and bio concentration of trace metals. The mean weathering rates estimated for major elements are in agreement with rates published for a range of forested soils from similar environments. Classifying the elements in order of decreasing relative mobility gives Mn> Mg> Ca> Na> K> P> Si> Al> Fe> Ti.

Bibliography of Canadian Geomorphology