长江上游土地利用变化与冲沟发生和演变

冲沟侵蚀是中国西部山区一个重要的环境问题。小流域研究表明，黄河和长江中的泥沙主要是冲沟侵蚀引起的。目前，长江上游80%的冲沟因被幼林草植被覆盖而处于非活跃期。到底这些冲沟系统是什么时候形成的？未来的暴雨和径流是否会激活这些冲沟系统？土地利用与景观结构对冲沟系统的发生、演变有何关系？基于这些问题，近几年来在中科院山地环境学“百人计划”和“国外引进杰出人才”项目及德国洪堡基金的资助下，中德科学工作者进行了合作研究。本文介绍了长江上游地区土地利用变化与冲沟发生、演变的部分研究成果。我们在西昌安宁河干暖河谷选择了两个冲沟系统一个位于西溪乡长山岭，一个位于大青梁子。为了定量评价土地利用对冲沟发育的影响，我们对研究小流域的航片、土壤剖面、泥沙堆积与土地利用历史等进行了详尽的综合对比分析。同时，对两个冲沟系统的大小和土壤流失的体积进行了详细的野外调查、测定和计算。据此，获得了研究流域的冲沟侵蚀速率。研究结果表明，长江上游数百年的持续景观演变，尤其是20世纪中期人为强烈的不合理农业垦殖和利用土地，造成了四川西南部大量冲沟系统的形成和发展，研究流域的冲沟侵蚀速率高达375t/hm2*a-1。采取成功的水土保持措施以控制冲沟侵蚀，对中国西南山地退化环境的生态修复具有重大实践意义。

Land Use Changes and Gully Developmentin the Upper Yangtze River Basin, SW_China

More than 80% of the gullies in Southwest China are not activetoday due to a cover with young vegetation. The objective of this study is to investigate the development of these gully systems and their relation to land use changes over the last 2000 years. The first investigations were carried out at the slopes bordering of the Anning Warm_Dry Valley of southern Sichuan in the territory of Xichang. Two gully systems were investigated in details. The size (length, average depth and width) and the volume of the gully system were measured in the field and calculated. The size of the surface catchment of the gully system was measured in the field, too. Air photos were analyzed, senior experts and farmers were interviewed for a detailed reconstruction of land use history.After several centuries of sustainable landscape development namely the intensive agricultural land use during the second half of the 20th century caused excessive floods and gullying in wide parts of southern Sichuan. Valley bottoms were flooded, rivers changed their position, many villages ceased there and lakes were filled with sediments. Gullying rates that could be reconstructed are unexpectedly high and strongly demand sudden successful measures of soil and water conservation.