Multiple Factor Analyses On Evolution Of Erosion Environment In Wind-water Erosion Crisscross Region Of Loess Plateau

The wind-water erosion crisscross region, which is located in the northwest of Loess Plateau, is the ideal region to study changes of erosion environment. There are significant transition characteristics of the ecological environment in this region and it is the frequent subrogation and staggered distribution region of farming and stockbreeding. The region with fragile ecological environment and serious soil and water loss has experienced long fluctuations in the evolution and is sensitive to global change. Therefore,7 typical profiles with clear cross-section of dark, loessial soil near the north-south dividing line of wind-water erosion crisscross region in Loess Plateau were chosen and nine samples were systematically selected on each profile. The original conclusions were shown as follows.1. Soil texture of the downtown area was obviously superior to that of the uptown area near the dividing line between north and south in wind-water erosion crisscross region. As to soil particle composition, surface soil had more sand than the other layers in the whole area. And the size orders of soil moisture were as follows: dark loessial soil water content> Malan loess water content> modern loess water content. Also it was drought gradually wet from northeast to southwest in wind-water erosion crisscross region. So we have known that the environment for developing loess was becoming more and more drought. In horizontal direction, Kd values showed that Shen Mu and Gao Jia Bao area were relatively warm and wet, however, Yong Ping area was relatively dry and cold.2. Geochemical elements showed that:since the formation of dark loessial soil, the wind-water erosion crisscross region in Loess Plateau has had a tendency to be dry with characteristics of decreasing rainfall, strong physical weathering, weak eluviations and weak pedogenesis. The climate fluctuated between warm and cold, wet and dry. However, dark loessial soil and topsoil profile indicated that western had an obvious warming phenomenon and eastern became arid. There were teeterboard torsional characteristics of erosion environmental with the expansion from eastern to southern and migration from western to northern. Nevertheless, this variety trend would fluctuate locally due to topography and man-made disturbances.3. Soil nutrient contents of C,N,P were relatively low in wind-water erosion crisscross region. Generally speaking, soil nutrient contents of 0-20cm were larger than that of 20-40cm, but there was little difference between surface nutrients and nutrients of the other layer. Therefore, it indicated that it was possible that potential nutrients were lost and leaching. We should not neglect that the amount of surface flow or base flow was higher.4. Pollen analysis showed that the biological climate of the wind-water erosion crisscross region in loess plateau was semi-arid desert steppe. Generally speaking, it was desert grassland climate during the formation period of Malan loess. While; it was mild and partially wet during the formation period of dark loessial soil. And now, erosion environment of the regions which implemented soil and water conservation measures become better, otherwise, erosion environment become worse.