The Hydrologic Implications of Soil Variability within a Small, First Order Semi-Arid Drainage Basin, Sevilleta LTER, New Mexico

The distribution of soils in a small first order drainage basin on the Sevilleta Wildlife Refuge reflect long term variability in moisture fluxes. The east-west orientation of the drainage results in differences in solar fluxes on north and south facing aspects and very different vegetation communities on the opposing hillslopes. The south facing hillslope is dominated by creostote and black gramma grassland and the north facing hillslope juniper trees and black gramma grasses. The soils on the north facing hillslope have more organic carbon, silt and calcium carbonate than soils on equivalent slope positions on the south facing hillslope. The depth to the calcic horizon is 30 cm on the north facing hillslope soils and only 5 cm on south facing hillslope. There are no clear catenary relationships for the soils on the sideslopes, because the slopes are convex to linear downslope. Within the headslope however, a catena is observed in the depth to calcic horizon and in the profile amount of calcium carbonate. The depth to the calcic horizon increases and the profile amount of calcium carbonate decreases down the catena.

Variability in soil physical properties produces concomitant changes in soil hydrologic properties. For example, soils on the north facing hillslopes will have higher soil moisture retention, and increased unsaturated hydraulic conductivity in the B horizons compared to soils on the south facing hillslope enhancing the initial differences in soil moisture produced by different solar fluxes.

The topographically induced variation in soil properties within the drainage means that the two sideslopes and the headslope respond differently during a rainfall event. Furthermore, as soil properties are evolving over time, the hydrologic properties of the different hillslopes have also changed during the evolution of the drainage basin.