Submitted to: Earth Surface Processes and Landforms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/23/2016
Publication Date: N/A
Interpretive Summary: Sediments stored in depressions contain a record of long term landscape erosion as well as evidence of major natural and anthropogenic disturbances. Accurate sediment chronologies are critical for interpreting these records. In this study erosion and sedimentation rates in three artificial ponds fed by small watersheds were determined using isotopes 210Pb and 137Cs. Documented management practices such as mesquite treatment and dredging, as well as long term trends could be identified in the time sequences determined from this technique. Overall 210Pb technique can be a reliable tool for estimation of erosion rates on small arid watersheds given proper sampling approaches. Better understanding and quantification of the factors that control soil erosion will provide guidance to inform national and international efforts to manage lands for erosion and productivity.
Technical Abstract: This study investigates erosion dynamics of the past 90 years on three small semi-arid watersheds with histories of grazing and vegetation change. Activity of 137Cs and excess 210Pb from 18 cores collected from sedimentation ponds were measured using a gamma spectrometer. The sediment was dated using a constant rate of supply (CRS) model. This study represents the first time that reservoir sediment accumulation rates determined from fallout isotopes have been verified by direct volumetric measurements of aggradation based on topographic surveys. Measured sedimentation in the ponds ranged between 1.9 and 2.3 cm y-1, representing average sediment delivery rates from the watersheds of between 0.6 and 2.0 t ha-1 y-1. These sediment delivery rates were in agreement with those established by other methods for similar catchments in the region. Past variations in sedimentation rates were identified and correlated with recorded history of anthropogenic disturbance. 137Cs and 210Pb methods are suitable for use in arid environments and can complement each other to increase reliability of erosion rate estimates. The abundance of stock ponds in southwestern US presents an opportunity to quantify historic