| Water-wind Erosion crisscross region is the strongest soil erosion area on the loess platea due to the combination effects of water and wind erosion. Previous studies concentrated on erosion by wind and water, mechanism, processes, spatial and temporal distribution, erosion intensity and influence factors. Research on wind erosion research is very limited compared to the water erosion, in which farmland wind erosion has few reports. This study chose a typical area of the water-wind erosion crisscross region named liudaogou watershedin shenmu county as the study area on the loess platea. Through the analysis of ~7Be background content and profile distribution characteristics for three types of local soil(silt loam(partial coarse, partial fine), silt loam(red) sand and silty clay loam), we estimated the feasiblity of the ~7Be meaurements to soil water erosion and wind erosion in this region. The spatial distribution of wind erosion was analyzed using ~7Be mearuments on plots with different slope gradients(0-25° with a interval of 5°). Moreover, on field scale, the spatial distribution of the isolines of wind erosion rate obtaied by ~7Be mearuments implied the effective resultant wind direction, field microreliefs and their influence scope of sloping cropland. This research mainly got the following conclusion:(1) The ~7Be background content and distribution characteristic profiles for three types of local soil both rainy season(2015.05-2015.10) and windy season(2014.10-2015.05) showed that the ~7Be content of the monsoon season were higher than that of the wind season, and it decresed exponential increasing the soil depth of trend in each plot as a whole. The ~7Be content and distribution depth of raniy season were greater than those of windy season, while the relaxation mass depth of rainy season was smaller than that of windy season. The ~7Be background contents of silt loam(partial fine), sand and silty clay loam of the rainy season were higher than those of the windy season at 2.4, 1.1 and 0.7 times respectively, suggesting the deposition of ~7Be in the rainy months was significantly higher than that in the windy season. As to the depth of detectable ~7Be in soil profile, silt loam(partial fine) had the deepest distribution depth(0 to 12.5 mm) in windy season, while sand had the deepest distribution depth in rainy season(0 to 15 mm). The relaxation mass depth of sand was the largest was(10.2 kg/m2) in windy season, while of silty clay loam(partial fine) was the largest(3.7 kg/m2) in rainy season.(2) The spatial distribution of soil wind erosion rate was analyzed based on ~7Be measuments on plots(1.7×5 m) with different slope grasients. The content of ~7Be showed that 5°-plot had the maxium average ~7Be value(231.2 Bq/m2), while the ~7Be content of 25°-plot had the minimum(145.3 Bq/m2). Both the isolines shape and values of ~7Be content were different from plot to plot. There were high or low ~7Be content for plots except 0°-plot. The ~7Be content increased gradually from southwest to northeast in 0° and 15° plot. For 5° plot, The ~7Be content increased then decreased from bottom to top slope along prevaling wind direction, and at the central slope area, it increased then decreased from southwest to northeast direction. For 10° plot, The ~7Be content undulated from bottom to top. According to the unit width sediment discharge of the north direction in eight directions of different gradients was largest, so the north wind erosion force was most erosion forceAccording to the ~7Be wind erosion rate estimation model, the wind erosion rate of 25° plot was the largest, reached 2790.7 t/(km2·a), while the wind erosion rate of 5° plot was smallest, just1536.5 t/(km2·a). In addition to 0° plot, wind erosion rate increased increasing the slope gradient.The high erosion center distributed at different parts of plots, suggests that there were small mounds microrelif. The curved shape and direction of upwind isolines center showed that small mounds caused air speeded up on the upwind direction airflow within certain scope, and intensified erosion. The low erosion center suggested a concave area. The negative wind erosion rate indicated a deposition.(3) On the field scale, study on two windward sloping farmland with sandy loam and clay loam soil using ~7Be measuments showed that the average wind erosion rate of sandy loam and clay loam was 1560.8 t/(km2?a) and is 694.3 t/(km2?a). The annual loss thickness of them averaged 1.2 mm and was 0.6 mm respectively. It impliecated the difference of erodiblility for different soil types. The sandy loam was easier to be blow away by wind than clay loam in this study. The wind erosion rate decreased from top to bottom for both slopes. The isolines of the wind erosion rate visually showed the effective resultant wind direction, scope of microreliefs and upwind direction of barriers. The distribution of wind erosion rate for both slopes showed the north wind was the effective resultant wind direction. For the sandy loam slope, there was some barrier upwind affected the wind, and there was a circular concave at the middle of slope with a diameter about 10 m. There were small mounds distributed at the middle area of the clay loam slope, and it changed wind erosion rate upwind area with a lengh around 10 m. |
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