Using¹³⁷Cs And⁷Be To Investigate The Soil Erosion Rate Of The Wind-Water Erosion Crisscross Region On The Loess Plateau

The Wind-Water Erosion Crisscross Region on the Loess Plateau of Chinaexperiences intense soil erosion due to the dual action of wind and water. Quantifying therate of water and wind erosion in the Loess Plateau is significant for soil and waterconservation programs. In this paper, the Liudaogou watershed in the Wind-Water ErosionCrisscross Region was selected for the study area. In order to exactly calculate the winderosion rate using the⁷Be technique, firstly a particle size correction factor P wasincorporated into the⁷Be-based water erosion model through the wind tunnel test. Thencombined with the¹³⁷Cs technique and⁷Be technique, the rate of water erosion and winderosion in the Liudaogou watershed were estimated quantitatively. At last, continuessimulated experiment of erosion by wind and rainfall were conducted in order to identifythe role of wind erosion on water erosion. The main results were as follows:(1) Sandy loess from the wind-water erosion crisscross region on the Loess Plateau ofChina was used in wind tunnel to test the feasibility of using the⁷Be technique to estimatewind erosion rate. Since wind erosion selectively removes finer particles of soil, the directuse of the⁷Be-based water erosion model tends to overestimate wind erosion rate as⁷Be ispreferentially associated with the fine particles. The results showed an exponential functionrelationship between Se/Soand the concentration of⁷Be at the eroded site (Seand Soare thespecific surface areas of eroded soil and the original soil, respectively). Thus, a particlesize correction factor P was incorporated into the⁷Be-based water erosion model. Thewind erosion rates calculated by the⁷Be-based wind erosion model were within5%errorcompared with the measured values, indicating that the corrected model estimates wind erosion rate fairly accurately and that the⁷Be technique could be used to estimate winderosion rate.(2) Using the⁷Be-based wind erosion model we estimated the wind erosion rate of thetwo slopes in the Liudaogou watershed during the drought period, the results showed thatthe content of⁷Be increased from the top of slope to the slope toe. The⁷Be content for Aslope (¹³⁷.53Bq/m²) is lower than that of B slope (212.58Bq/m²). With the decrease ofslope length, the rate of wind erosion increased firstly and then decreased and againincreased at last. The wind erosion rate for A slope (1425.5⁷t/km²) was higher than that ofB slope (880.98t/km²), which proved that the soil texture had a significant influence on thewind erosion.(3) Eight hillslopes with different aspects but similar slope inclination, length, andheight were selected in the Liudaogou watershed in the Wind-Water Erosion CrisscrossRegion. Total soil loss on different slopes was analyzed quantitatively using¹³⁷Cs.Meanwhile particle size distribution and soil organic matter of surface soil at differentslope sites were analyzed. The results showed that soil particle size distribution andorganic matter content at the uppermost site of different hillsides were significantlydifferent, which demonstrated a great difference in the intensity of wind erosion ondifferent hillside aspects. Using the erosion rate of the east facing hillside (8609t/(km2·a))as the benchmark we calculated the wind erosion rates (or wind deposition rates) of theother slopes. The wind deposition rate for the southeast and south facing hillsides were299t/(km2·a) and20⁷t/(km²·a), respectively, and the percentage of wind erosion on differenthillsides ranged from16.36%to22.0⁷%. Wind erosion on the northwest facing hillsidewas highest (2439t/(km²·a)). The average wind erosion rate of slope in this region was1455t/(km²·a)).(4) Sandy loess from the wind-water erosion crisscross region on the Loess Plateau ofChina was selected for continues simulated experiment of erosion by wind and rainfall.The results showed that the wind erosion had an impact on the runoff duration, the averageflow velocity along the slope, the amount of soil erosion in rainfall experiment and theamount of runoff. The runoff duration, the average flow velocity along the slope and theamount of soil erosion in rainfall experiment after wind tunnel test were all lower than thatof the single rainfall experiment, but the amount of runoff were higher. With the increasing of wind speed in experiments, the runoff duration, the average flow velocity along theslope and the amount of soil erosion in rainfall experiment after wind tunnel test weregradually decreasing, but the amount of runoff was gradually increasing. We defined the△f was the coupling intensity of water and wind erosion and its value was the differencebetween the amount of rainfall erosion after wind erosion and the amount of single watererosion. The higher the wind speed and the rainfall intensity were, the lower the value of△f was.