QUANTIFYING THE INFLUENCE OF CALCIUM CARBONATE ACCUMULATION ON THE HYDRAULIC PROPERTIES OF SEMIARID SOILS: SEVILLETA NATIONAL WILDLIFE REFUGE, NEW MEXICO

Soil properties have a major influence on the partitioning of rainfall into infiltration and runoff. Hence, they determine the water available for aquifer recharge, stream flow, and ecosystem processes. Quantifying hydraulic properties for soils requires the use of pedotransfer functions; however no previous functions have taken into account calcium carbonate accumulation at depth and how the calcium carbonate accumulation affects the rate of water movement into the soil. The accumulation of calcium carbonate in semiarid soils increases with age and produces systematic morphological changes in calcic horizons. 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 profile. A semiarid site in the Sevilleta National Wildlife Refuge, New Mexico, has been excavated gradually to 1.45 m with each soil horizon characterized hydrologically using a tension infiltrometer. Carbonate concentration and bulk density was also measured for each horizon. At the site carbonate development increased with depth to a recognized stage three level. The soil texture is predominately sandy loam. Saturated hydraulic conductivities range from 9*10^-4 cm sec^-1 to 8*10^-2 cm sec^-1. Dry bulk densities vary from 1.42 g cm^-3 to 1.85g cm^-3. Calcium carbonate levels range from 4 to 29%. Preliminary results indicate that as the calcium carbonate accumulates with depth and fills in the pore spaces of the soil substrate, the water flow decreases as reflected by a reduction in hydraulic conductivity. To determine the changes in soil hydraulic properties due to calcium carbonate alone, we use pedotransfer functions based on the measured soil texture assuming that the measured hydrologic properties deviate from that indicated by the pedotransfer functions. This difference represents the changes due to calcium carbonate accumulation.