THE HYDROLOGIC IMPACT OF BIOTURBATED SOILS FOUND IN ANIMAL MOUNDS, SEVILLETA WILD LIFE REFUGE, NEW MEXICO

In the arid south west United States water resources are coming under increased pressure due to increased demand and a more recent drought. Studies have shown that for many rangeland areas, during the Holocene, there has been little vertical infiltration of precipitation beyond the rooting depths of plants. One possible process facilitating water movement beyond the rooting zone on flat grassland areas is through altering the soil hydraulic parameters through bioturbation.

Animal mounds are a common feature of the grasslands of the eastern Sevilleta Wild life Refuge. They form low (20-30 cm high), 3-4 meter diameter wide areas of bioturbation characterized by an absence of vegetation in an area of otherwise continuous grassland. As is typical of bioturbated soils, soil textures are relatively uniform with increasing soil depth, an absence of pedogenic horizons and a significant change in soil structure, density and porosity. Concomitant with these properties are changes in the hydraulic properties of the bioturbated soil. Soil moisture retention especially in the upper horizons is reduced and hydraulic conductivity is increased. To determine the magnitude of these changes we described and analyzed two soils, one within an animal mound and the other immediately adjacent to the mound. The differences in hydrological response to the same precipitation event between the two soils were quantified using Hydrus 1- D.