MEASURING SOIL REDISTRIBUTION IN SEMIARID GRASS AND SHRUB COMMUNITIES USING 137-CESIUM

Authors: Ritchie, Jerry; Herrick, Jeffrey - Jeff; RITCHIE, C - CONSULTANT

Submitted to: International Association of Hydrological Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/10/2003
Publication Date: 4/15/2003
Citation: Ritchie, J.C., Herrick, J.E., Ritchie, C.A. 2003. Measuring in semiarid grass and shrub communities using 137Cesium. In: E. Servat, W. Najem, C. Leduc and A. Shakeel(eds.). Hydrology of Mediterranean and Semiarid Regions. International Association of Hydrological Sciences Publication. 278.

Interpretive Summary: Understanding the soil stability of Northern Chihuahuan Desert landscapes is key to developing management strategies to conserve this landscape. In this study we used radioactive fallout cesium-137 to measure soil movement (i.e., soil stability) under different vegetation communities at the USDA-ARS Jornada Experimental Range in New Mexico. The cesium-137 data showed that significant soil redistribution has occurred at the shrub sites with net soil accumulation under the shrub canopy. The data shows a significant plant-interspace scale soil redistribution pattern at mesquite dune vegetation with little Cs-137 found between dunes while in the arid grassland sites with black grama grass and tobosa grass Cs-137 data show a homogeneous distribution of soil resources with little evidence of net soil movement from the area in the past 50 years. Our data clearly show that soil redistribution is related to vegetation type and that fallout Cs-137 can be effectively used to quantify patterns of soil redistribution at both plant-interspace and Jornada basin scales.

Technical Abstract: Soil redistribution across semiarid landscapes is often associated with changing vegetation patterns. Semiarid grasslands tend to have uniform patterns of soil properties while shrublands have nonuniform patterns of soil properties. In the 1950's and 1960's radioactive Cesium-137 was deposited uniformly across the landscape from atmospheric fallout from nuclear weapon tests. Once in contact with the soil, Cs-137 is rapidly and strongly adsorbed to soil particles and any redistribution is due to the physical movement of soil particles. Thus, by measuring Cs-137 redistribution across the landscape, soil redistribution can be estimated. Soil profiles were collected from grass (Black Grama and Tobosa) and shrub (Tarbush and Mesquite) sites at the USDA-ARS Jornada Experimental Range in the Northern Chihuahuan Desert in New Mexico USA. Concentrations of Cs-137 were determined in these soil profiles. At the Black Grama and tobosa sites, Cs-137 was uniformly distributed across the sites. At mesquite sites, Cs-137 was concentrated in the dune area under mesquite shrubs with little to no Cs-137 in the interdune areas indicating soil redistribution from the interdune space to the dune. At the tarbush sites Cs-137 concentration was variable. Calculated erosion rates varied with vegetation type and within vegetation type. The black grama showed no net soil loss, while the tobosa site showed a net soil deposition of 5 t/ha/yr. The tarbush site had both soil erosion and deposition depending on sample location. The mesquite sites were also highly variable depending on location of the site and whether samples were taken from the dune area under the mesquite plant or from the space between dunes. Interdune areas always showed soil loss while some dunes showed gains in soil and others showed soil loss. This study shows that Cs-137 data from soil profiles can provide insights into the redistribution patterns of soil resources in these semiarid grass and shrub communities.