Tracing the lateral movement of sediment through an arid landscape at seasonal, centennial, and millennial scales

As a result of desertification, semi-arid grasslands, in many parts of the world, have been displaced by woody shrubs, such as grasslands at the Jornada Experimental Range, New Mexico. In this northern Chihuahuan Desert ecosystem, grasslands on the piedmont slope and basin floor landforms have been exceptionally vulnerable to woody shrub expansion (Chapter 1). As shrubs invade perennial grasslands, the length, number, and arrangement of connected bare patches coalesce to create sediment transport corridors. Future droughts will likely result in the growth and coalescences of these bare erodible soil surfaces and lead to increased in wind and water erosion. Transport of sediments by wind and water are key components in our understanding of desertification. However, the lateral movement and transport of sediments over varying temporal time scales has been poorly characterized in arid landscapes.;This study used naturally occurring and anthropogenic radionuclides to study the rates of sedimentary processes and sediment redistribution at: seasonal, centennial, and millennial temporal scales. 7Be was used for seasonal processes on 3-6 month time scales to test new ways to alter the lateral movement of sediments (Chapter 2). Excess 210Pb and 137Cs was used for depositional processes in low-lying areas for centennial scales (Chapter 3), and optical and 14C dating were used to date periods for erosion and soil development, which occurred over millennial time scales (Chapter 4).;At the seasonal scale, short-lived radionuclide measurements indicated sediment retention structures (aka Connectivity-Modifiers) contained 30 to 50% higher surface activities than the neighboring control plots, which indicated that changes in connectivity can influence sediment movement. At the centennial scale, excess 210Pb and 137Cs measurements, in combination with optical and 14C dates, demonstrated that sedimentation in low-lying vegetated grasslands was ∼ 84% higher during the last 50 years than compared to late Holocene rates. At the millennial scale. Optical and 14C measurements, in addition to stable C isotopes, provides evidence that C3 ecosystem experienced periods of wind erosion, was present around 42 ka yrs. B.P., and was later impacted by higher water table at 13.9 ka yrs B.P.