QUANTIFYING THE INFLUENCE OF CALCIUM CARBONATE ACCUMULATION ON SOIL MICRO-MORPHOLOGY OF THREE SEMIARID SOILS: SEVILLETA NATIONAL WILDLIFE REFUGE, AND FITE RANCH, NEW MEXICO

Calcium carbonate accumulation is a major influence in semiarid soil development. As it accumulates over time in soils, systematic morphological changes occur in the calcic horizons affecting the way water infiltrates the soil profile. Studies have recognized six stages of calcic horizon development recording the gradual accumulation of calcium carbonate cementing the matrix of soils until eventually producing an impermeable layer within the soil. Two semiarid sites in the Sevilleta National Wildlife Refuge, New Mexico and one semiarid site at Fite Ranch, New Mexico have been excavated with eighteen total samples taken for thin section analysis. A modal analysis was completed using a petrographic microscope and a 0.5 to 1mm search pattern using a mechanical stage. Carbonate concentration, bulk density, and saturated hydraulic conductivity were also measured for each soil horizon. Results show that as the nodular, clotted, and disseminated types of calcium carbonate accumulated with depth, the intragranular pore space decreased proportionally. This decrease in pore space of the soil framework is accompanied by a reduction in hydraulic conductivity. In the samples with the most calcium carbonate cementation, the primary pore space has been entirely occluded. Secondary porosity was created by dissolution of the framework grains and subsequent precipitation of micrite. Filamentous carbonate is present filling some pore spaces and is thought to be attributed to growth of bacteria since carbonate deposition by water is a minor factor at depth.