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CLAY MINERALS AND THE ACCUMULATION OF SOIL ORGANIC MATTER IN NORTHWESTERN U.S. FORESTS
Citation:
Johnson, M G. AND J. R. Glasmann. CLAY MINERALS AND THE ACCUMULATION OF SOIL ORGANIC MATTER IN NORTHWESTERN U.S. FORESTS. Presented at 37th Annual Meeting of The Clay Minerals Society, Chicago, IL, June 24-29, 2000.
Description:
Globally soils are an important terrestrial reservoir of carbon, storing approximately 3 times the carbon held in vegetation and 2 times the amount contained in the atmosphere. With the potential for global climate change it is imperative that world soils continue to be a sink for carbon. Because clay minerals play an important part in the stabilization, and thereby the sequestration of soil organic matter, we developed a project to investigate their role in the accumulation of soil organic matter across a range of forested soils in the Pacific Northwest. We selected 11 sites in Oregon (Coast Range Mountains and Cascade Mountains) and Washington (Olympic National Park) covering a range of forest types and environments to investigate the role of clay minerals and the accumulation of soil organic matter. The eastern end of the sites is a Juniper (Juniperus occidentalis) forest growing in soils developed in Mount Mazama ash. Also included are high- and low-elevation Douglas fir (Pseudotsuga menziesii) forests growing on soils from old glacial deposits and recent glacially worked volcanics. A Ponderosa pine (Pinus ponderosa) site growing in soil derived from volcanic and colluvial deposits. Coastal forests include Sitka spruce (Picea sitchensis) and Douglas fir growing in soils from old marine sediments and basalts. Annual precipitation values range from less than 30 cm for the Juniper site to more than 300 cm for the coastal Douglas fir and Sitka spruce sites. Soil samples were collected from three depths: the organic rich 0-20 cm surface mineral soil layer and two deeper subsurface layers 20-50 cm and 50-100 cm. The mineral composition of clay fraction of each sample was determined by X-ray diffraction and transmission electron microscopy. The clay mineralogy of the 11 sites is quite diverse, reflecting the soil parent material, age and weathering environment. The sites in Washington are dominated by calorie, mica and hydroxy-interlard vermiculite. The soi