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We measured dissolved organic carbon (DOC) in soil solutions collected from the A and B horizons of a Spodosol in central New Hampshire. DOC averaged 33 mg/L in the A2 horizon and declined to 2 to 3 mg/L, similar to stream water concentrations, in the B horizon. DOC concentrations in A2 horizon lysimeters were inversely related to the volume of water collected per day; we observed maximum concentrations (approximately 55 mg/L) during September. In the B horizon lysimeters, DOC levels were relatively constant, as were levels in stream water. In laboratory experiments, DOC in A2 horizon soil solution was rapidly absorbed by B horizon soils. The equilibrium DOC concentrations predicted by adsorption isotherms agreed to within 1 to 2 mg/L with lysimeter results. Our results suggest that coprecipitation of iron and organic matter in the upper B horizon, a process central to podzolization, largely controls the concentration of dissolved organic carbon in stream water at Hubbard Brook.
McDowell et al. (Sun,) studied this question.