The Wind-Water Erosion Crisscross Region on the Loess Plateau of China experiences intense soil erosion due to the dual action of wind and water. Quantifying the rate of water and wind erosion in the Loess Plateau is significant for soil and water conservation programs. In this paper, the Liudaogou watershed in the Wind-Water Erosion Crisscross Region was selected for the study area. In order to exactly calculate the wind erosion rate using the 7Be technique, firstly a particle size correction factor P was incorporated into the 7Be-based water erosion model through the wind tunnel test. Then combined with the 137Cs technique and 7Be technique, the rate of water erosion and wind erosion in the Liudaogou watershed were estimated quantitatively. At last, continues simulated experiment of erosion by wind and rainfall were conducted in order to identify the 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 of China was used in wind tunnel to test the feasibility of using the 7Be technique to estimate wind erosion rate. Since wind erosion selectively removes finer particles of soil, the direct use of the 7Be-based water erosion model tends to overestimate wind erosion rate as 7Be is preferentially associated with the fine particles. The results showed an exponential function relationship between Se/So and the concentration of 7Be at the eroded site (Se and So are the specific surface areas of eroded soil and the original soil, respectively). Thus, a particle size correction factor P was incorporated into the 7Be-based water erosion model. The wind erosion rates calculated by the 7Be-based wind erosion model were within 5% error compared with the measured values, indicating that the corrected model estimates wind erosion rate fairly accurately and that the 7Be technique could be used to estimate wind erosion rate. (2) Using the 7Be-based wind erosion model we estimated the wind erosion rate of the two slopes in the Liudaogou watershed during the drought period, the results showed that the content of 7Be increased from the top of slope to the slope toe. The 7Be content for A slope (137.53 Bq/m2) is lower than that of B slope (212.58 Bq/m2). With the decrease of slope length, the rate of wind erosion increased firstly and then decreased and again increased at last. The wind erosion rate for A slope (1425.57 t/km2) was higher than that of B slope (880.98 t/km2), which proved that the soil texture had a significant influence on the wind erosion. (3) Eight hillslopes with different aspects but similar slope inclination, length, and height were selected in the Liudaogou watershed in the Wind-Water Erosion Crisscross Region. Total soil loss on different slopes was analyzed quantitatively using 137Cs. Meanwhile particle size distribution and soil organic matter of surface soil at different slope sites were analyzed. The results showed that soil particle size distribution and organic matter content at the uppermost site of different hillsides were significantly different, which demonstrated a great difference in the intensity of wind erosion on different hillside aspects. Using the erosion rate of the east facing hillside (8609 t/(km2·a)) as the benchmark we calculated the wind erosion rates (or wind deposition rates) of the other slopes. The wind deposition rate for the southeast and south facing hillsides were 299 t/(km2·a) and 207 t/(km2·a), respectively, and the percentage of wind erosion on different hillsides ranged from 16.36% to 22.07%. Wind erosion on the northwest facing hillside was highest (2439 t/(km2·a)). The average wind erosion rate of slope in this region was 1455 t/(km2·a)).
(4) Sandy loess from the wind-water erosion crisscross region on the Loess Plateau of China 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 average flow velocity along the slope, the amount of soil erosion in rainfall experiment and the amount of runoff. The runoff duration, the average flow velocity along the slope and the amount of soil erosion in rainfall experiment after wind tunnel test were all lower than that of 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 the slope and the amount of soil erosion in rainfall experiment after wind tunnel test were gradually 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 difference between the amount of rainfall erosion after wind erosion and the amount of single water erosion. The higher the wind speed and the rainfall intensity were, the lower the value of △f was.
Keywords: Water erosion rate; Wind erosion rate; 7Be; 137Cs