WWRC 84-04
Processes Controlling the Composition of Infiltrating Water in Forested Mountain Watersheds
Abstract
Chemical weathering in a high-elevation pine forest was
studied by analysis of percolating soil solutions and associated
solid phases. In the shallow soil (above 40 cm), soil-water
chemistry is controlled by biological processes -- uptake by
plants and decay in the litter layer. Below 40 cm mineral
weathering becomes more important as a control, but solution
compositions are so variable in space and time that it is
impossible to define a simple weathering stoichiometry.
Kaolinite is forming in the upper part of the soil profile and
smectite in the lower part, although solution compositions
indicate that kaolinite should be the more stable phase at all
depths.
Dissolved organic carbon (DOC) values are high (average
38 mgC/l) in the forest floor litter, and decrease with depth in
the mineral soil. In clay-rich, low-permeability soil the DOC
loss and acquisition of cations take place close to the surface,
whereas in more permeable soils DOC transport and chemical
weathering extend to greater depths. There is some enhanced
transport of Al and Fe as a result of complexing by organic
acids. The mechanisms by which DOC is removed from solution are
not clear.
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