| The Yunjiang dry-hot valley region (DHV), located in the upper and middle reaches of the Yunjiang river in Yunnan province, is the most concentrated and continuous distributed dry-hot valley in ChinaYu. Ephemeral gully erosion is a serious problem in the Yunjiang DHV, which resulted from the widely distributed steeper cultivated slopes as will as concentrated rainfall. Ephemeral gully erosion can not only increasing river sediments, but also result in the deterioration of soil structure, reduction of effective soil thickness, soil nutrient content, available soil water content as will as the degradation of soil producitivty, and capable of threatening local grain production. However, little research has been conducted on the spatial-temporal distribution and environmental factors of ephemeral gully erosion in the Yunjian DHV.In this study, a typical DHV watershed named LaoZhai where located in the right bank of yuanjiang river basin was selected as case area. The developing and characteristics (position, shape, size et al.) of ephemeral gullys were monitored in a growing season, the types of soil and water conservation measures, types of land use, topography indexes as will as soil physical and chemical properties were investigated. The purpose were to characterize spatial-temporal distribution of, and to evaluate the impact of environmental factors on ephemeral gully erosion in DHV, and basically have the following results and conclusion:(1) Ephemeral gullys can be divided into five categories by it’s cause in the case area:boundary ditch, ditch, pipeline ditch, road ditch and terrain ditch. Terrain ditch was the main types, which accounting for66.8%of the total length of ephemeral gully in the study area. From head to tail, a increasing of the depth of ephemeral gully was found, while no significant change in width of ephemeral gully, the wide depth ratio in the study area were almost greater than1.(2) During the monitoring period (in a single growing season), the total soil eroded by ephemeral gully erosion was251.09t. with the ephemeral gully erosion modulus was453.50t·km-2a-1and ephemeral gully density was8342.10mkm-2(3) The temporal distribution of ephemeral gully erosion in a growing season shown a trends of "after farming<before farming<after harvesting ", which indicate that farming cannot eliminate all the ephemeral gully in the DHV. The step slops in DHV had hindered the employing of mechanized farming, and the destruction to the ephemeral gully by manual farming is weaker than that by mechanized farming. This is also an important characteristic of ephemeral gullys development in the DHV.(4) Ephemeral gullys tend to development in area of slope ranged from25°to30°, and shown a trends of woodland> corn> orchard> shrub land in different types of land use, indicate that the ephemeral gullys erosion was increasing with the increasing of artificial disturbance to crop land in DHV. the crop land may abandoned cultivation when the ephemeral gullys erosion was really eriously. Generalgener, ephemeral gully developed in land which didn’t have soil and water conservation measures was more serious than that of have. However, soil and water conservation measures of horizontal stage in the orchard didn’t have significant to control effect on the developing of ephemeral gully, this may because water pipe can cause ephemeral gully. Forth more, ephemeral gully mainly developed in the soils with high bulk density, high organic matter and sand content, while with low of clay content.(5) Principal component analysis shown that the main environmental factors affect on the developing of terrain ditchs were slope gradient, soil and water conservation measures, land use and soil clay content, and the slope gradient was the key environmental factor controls on terrain ditchs. |
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