不同时间尺度洛川塬地貌演化与侵蚀量估算

LANDSCAPE EVOLUTION AND EROSION OF LUOCHUAN TABLELAND(CENTRAL CHINESE LOESS PLATEAU)AT DIFFERENT TIME SCALES

黄土高原降雨集中与黄土沉积松散等特性,使地表侵蚀严重。洛川塬作为黄土高原中部典型的地貌体,堆积了完整的第四纪黄土-古土壤序列,成为揭示我国乃至东亚第四纪环境演变的重要地质记录。另一方面,现在洛川塬遭受强烈侵蚀作用,沟谷密度大于2km/km^2。对洛川塬地质时期侵蚀程度的定量认识有助于全面理解黄土高原堆积和侵蚀过程,进而定量判断在自然过程和人为作用下黄土高原侵蚀的未来趋势。本文利用GIS和RS技术,结合第四纪地质的研究,在定量提取地貌数据和获得侵蚀期年代的基础上,分析了洛川塬地貌特征和具代表性的黑木沟侵蚀状况,认为洛川塬已经进入地貌发育的壮年时期。通过地统计方法中的空间插值恢复古地形面,得到洛川塬自550ka以来平均侵蚀模数约为272.6t/km^2·a,黑木沟自250ka以来侵蚀模数为464.1t/km^2·a;基于通用土壤流失方程得到洛川塬现在的侵蚀模数达到4389t/km^2·a。这些结果显示,现代洛川塬的侵蚀强度是550ka以来平均侵蚀强度的16倍。本文从定量的角度证明,人类的土地利用等加强了水土流失强度。

Since loess is loose and rain mainly falls in summer time, severe erosions occurred in Chinese Loess Plateau. Luochuan loess tableland is a typical landform and sedimentary basin in this region, it preserves a complete Quaternary loess-paleosol sequence which is a good archive of Quaternary environment changes in China and East Asia. On the other hand, because of strong erosion in the Luo River catchment and its tributaries occurred, the Luochuan loess tableland and its adjacent region has a valley density greater than 2km/km2. To quantitatively understand past erosion processes in the Luochuan loess tableland will be helpful to understand dust accumulation and erosion dynamics in the Loess Plateau, and ,to separate natural and human impacts on the landscape processes and environmental changes. In this paper, we use geological and remote sensing data as well as the Geographic Information System（GIS） technique to analyze erosions in the Luochuan loess tableland and the Heimu Gully. According to Strahler＇s drainage theory, the Luochuan loess tableland has entered the prime time of erosion and has an average erosion modulus of 272.6t/km^2. a from S5 （about 550ka）to the present; the Heimu gully has an average erosion modulus of 464. 1 t/km2 · a since the $2 （ around 250ka） to the present. Based on the universal soil loss equation,the current erosion modulus is 4389t/km2.a in the Luochuan loess tableland. We can see that the recent erosion rate is 16 times greater than that in the natural past in our investigating place. Human activity such as land use and destruction of vegetation may exacerbate the loess erosion.