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Title: Quantifying decadal-scale erosion rates and their short-term variability on ecological sites in a semi-arid environment

item POLYAKOV, V.O. - University Of Arizona
item Nearing, Mark
item STONE, J.J. - Retired ARS Employee
item Holifield Collins, Chandra
item Nichols, Mary

Submitted to: Catena
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/22/2015
Publication Date: 11/24/2015
Publication URL:
Citation: Polyakov, V., Nearing, M.A., Stone, J., Holifield Collins, C.D., Nichols, M.H. 2015. Quantifying decadal-scale erosion rates and their short-term variability on ecological sites in a semi-arid environment. Catena. 137:501-507.

Interpretive Summary: Ecological Site Descriptions (ESD) are currently being developed and mapped for the western states of the US. These ESDs describe the different types of ecological plant communities that can exist on a piece of land, based on the type of soils, topography, and climate at that location. The State and Transition Model concept describes not only the types of ecological plant communities that can be found on a particular ecological site, but also the drivers that cause one plant community to shift to another. For many ecological sites soil erosion can play a significant role in how one plant community transitions to another, for example, as a site degrades from a healthy condition to a poor one. In this study we used two existing tools to measure soil erosion at different time scales in order to better understand the role that soil erosion might play in such transitions. We measured soil erosion using an isotopic technique with 137Cs, which quantifies erosion as an average over approximately the last 50-60 years, and with a rainfall simulator, which characterizes erosion at essentially a single point in time. We learned that the measurements at a single point in time could vary quite a lot depending on the conditions at the location at that point in time, for example, if the measurements are made shortly after a fire. The longer term 137Cs measurements probably have more meaning in terms of characterizing the long-term differences in soil erosion rate as a function of plant community, but the rainfall simulator measurements are more useful to identify processes that have the potential to impact the ecological system and potentially cause a change in the state of the site.

Technical Abstract: Soil erosion rates on six semi-arid loamy upland rangeland sites located in southeastern Arizona were measured using a rainfall simulator and 137Cs fallout methods. Site characteristics that have the greatest effects on soil erosion and runoff were identified. Long term (50 years) soil erosion rates as estimated using 137Cs method varied between 5.1 t ha-1 y-1 and 11.0 t ha-1 y-1and showed significant differences between Historic Climax Plant Community and Mesquite/Native states of the States and Transition Model. Erosion rates measured under simulated rainfall varied greatly, as much as 8-fold on the same location, depending on the time of the simulation. Temporal variability of erosion rates within a site was in some cases much greater than inter-site differences. This variability was attributed to natural or management driven changes of plant community and soil characteristics. For meaningful interpretation rainfall simulation results must be placed in the context of the range of possible vegetation and surface conditions of a given ecological site.