AN EXAMPLE OF SOIL PROCESSES IN THE ABIES AMABILIS ZONE OF CENTRAL CASCADES, WASHINGTON

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Abstract
Tension lysimeters were used to monitor continuously the soil solutions from the O2, A2, IIB2hir, and IVB32 of a Podzol (Cryandept) in the central Cascades, Washington. Precipitation, forest throughfall, and stream water were also collected. Averages of three years of data show a drop in pH as the meteoric water passes through the canopy and the forest floor. Solutions leaving the IIB2hir show an increase in pH; a further increase occurs in the IVB32 and the stream. There is an increase in the summation of the major cations (Ca, Mg, K, and Na) and electrical conductivity as the precipitation penetrates the canopy; a further increase occurs as the solutions pass the forest floor. A lowering of these parameters is recorded in the solutions leaving the IIB2hir. Below the IIB2hir, the concentration of the cations, the electrical conductivity, and the pH increase. The concentrations of the major rock-forming elements, Si, Al, and Fe, are low in the precipitation. In the soil, soluble Si is the most abundant at any level, and Fe is the least. Al has intermediate values. In general, the three elements have a minimal level after passing the IIB2hir, but they increase below it. Total N decreases from the precipitation to the IIB2hir, where a minimum value is obtained; it increases below. Total P follows a similar trend. Mobile fulvic acids, seen to arise in the 0 horizons, are reduced by 60 percent to 70 percent within the IIB2hir. According to these data, the IIB2hir delineates the lower boundary of the biopedological compartment that starts at the top of the canopy. The geochemical compartment starts below the IIB2hir and includes the IVB32 and bedrock material in contact with groundwater. It is suggested that the pH and the anionic balance in the upper compartment are controlled by soluble organic acids, whereas the bicarbonate system dominates the lower. The presence of these compartments points to the invalidity of the use of stream and groundwater data to delineate the biopedological sector of a forest ecosystem. © Williams & Wilkins 1977. All Rights Reserved.

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