Scale effects on runoff and soil erosion in rangelands: observations and estimations with predictors of different availability

Authors: MARTINEZ, GONZALO - Universidad De Cordoba; Weltz, Mark; Pierson Jr, Frederick; SPAETH, KENNETH - Natural Resources Conservation Service (NRCS, USDA); Pachepsky, Yakov

Submitted to: Catena
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/14/2016
Publication Date: 1/6/2017
Citation: Martinez, G., Weltz, M.A., Pierson, F.B., Spaeth, K., Pachepsky, Y.A. 2017. Scale effects on runoff and soil erosion in rangelands: observations and estimations with predictors of different availability. Catena. 151:161-173.

Interpretive Summary: Water runoff and soil erosion are the key processes to account for in agricultural land management decisions. There have been indications that the scale (i.e. size of the land parcel) affects the runoff coefficient (percentage of water lost to runoff), and sediment yield (amount of soil lost per unit of water lost). The objective of this work was to evaluate the importance of this effect for predictions and management decisions in rangelands. We analyzed data from the National Range Study database containing data from 444 coupled large and small plot field experiments. We found a substantial scale effect not only on the runoff coefficient and sediment yield, but also on the relative importance of runoff and erosion predictors. Results of this research are expected to be widely used by the various groups of professionals concerned with rangeland management and evaluation of ecosystem services derived from rangeland conservation practices.

Technical Abstract: Runoff and erosion estimates are needed for rangeland management decisions and evaluation of ecosystem services derived from rangeland conservation practices. The information on the effect of scale on the runoff and erosion, and on the choice of runoff and erosion predictors, remains scarce. The objective of this work was to evaluate this effect with the rich National Range Study database containing data from 444 coupled large (3.05 m by 9.1 m) and small (0.61 m by 1.22 m) plot field-experiments. With data from both plot sizes, we assessed the usefulness of adding site-specific soil surface information to basic soil and rainfall data in order to estimate runoff and erosion in rangelands. We observed the scale-dependence of runoff coefficient and sediment yield. Smaller values of both variables were found at large plots as compared to small plots. Regression trees were used to build predictive relationships and evaluate the relative importance of predictors. Rainfall and basic soil properties were identified as the major predictors of runoff coefficients and sediment yields at both scales. Differences in the importance of predictors were observed between the two plot sizes and between the prediction of runoff and sediment yield. Antecedent soil moisture was not as important as rainfall parameters. Overall, including site-specific soil surface properties did not improve the predictability of the runoff coefficient and sediment yield. The difference in runoff and sediment yield between small and large plots is found most likely because the small plots only contain a single soil/vegetation expression. In the large plots there is a matrix of vegetation clumps and bare interspaces in a non-uniform pattern. The variability of runoff and sediment yield may depend on how this pattern expresses itself in each of the large plots. More research or a different approach is required to account for vegetation-driven spatial hydrologic processes and its influence on rangeland runoff and soil erosion processes.