Processes Controlling the Composition of Infiltrating Water in Forested Mountain Watersheds

摘要

Chemical weathering in a high-elevation pine forest was studied by analysis of percolating soil solutions and associated solid phases. In the shallow soil, 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. 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.