1956-2010年三江源区水土流失状况演变

为研究三江源区水土流失状况变化及其可能成因，基于1956—2010年三江源区水文、气象观测资料以及遥感数据，借助Mann-Kendall趋势检验法分析了输沙量的年际变化，并采用双累积曲线、RUSLE（修正的通用土壤流失方程）分析了水土流失状况变化的可能成因.结果表明:① 三江源区输沙量表现为黄河源区>长江源区>澜沧江源区，输沙量最大值均出现在6—8月，最小值均出现在12月—翌年1月.② 各流域输沙量的年际变化较大，并且均以20世纪80年代为最大.2005—2010年黄河源区输沙量较多年平均值减少32.25%，而长江源区和澜沧江源区分别相应增加24.76%和41.86%.黄河源区土壤水蚀量增加明显，长江源区不同河段各有增减，澜沧江源区土壤水蚀强度降低.③ 引起水土流失状况变化的原因主要包括气候变化和生态工程两个方面.即① 降雨量的增加导致降雨侵蚀力和径流量增加，使得土壤水蚀量和河流输沙量有所增加；② 生态工程实施后，土壤中w（有机质）虽有所增加，但仍明显低于1980年的水平.尽管植被覆盖度有所提高，但对水土保持功能起重要作用的根系层恢复却较为缓慢，因此，土壤保持功能基本上未得到提高. 

Soil Erosion Status Variation and Attribution in the Three-River Headwaters Region during 1956-2010

The Three-River Headwaters Region (TRHR) in China is a critical ecological barrier as well as soil and water conservation area. In order to analyze soil erosion status variation and find possible causes, the intra-annual distribution and inter-annual variability of sediment load were investigated based upon actual observation data from 1956-2010, by using Mann-Kendall test and other statistical approaches. Meanwhile, we tried to find the possible causes of soil erosion status change by using meteorological, remote sensing, soil sampling data and the double mass curve, Revised Universal Soil Loss Equation (RUSLE). The results showed that:(1) The sediment load in the Yellow River Basin (YRB) was larger compared with that in the Yangtze River Basin (YARB) and the Lancang River Basin (LRB). The continuous three months' maximum sediment load appeared in June, July and August, while the minimum monthly value usually appeared in December and January. (2) The fluctuation of sediment load was relatively violent; the highest decadal value appeared in the 1980s. Over the period of 2005-2010, sediment load in YRB was -32.25% lower than mean value; however, for YARB and LRB, it was 24.76% and 41.86% higher than mean value, respectively. Soil erosion amounts in YRB increased obviously; however, the change of soil erosion amount in YARB did not show a consistent trend. The soil erosion intensity in LRB decreased to some extent. (3) The causes of soil erosion status change include two aspects of climate change and ecological engineering. On the one hand, increased rainfall led to increase of rainfall erosivity and water discharge, so that soil erosion amount and sediment load increased. On the other hand, after the implementation of ecological projects, the soil organic matter content increased, but it was still lower than the level in 1980. Vegetation coverage increased over the period 2000-2010; however, the root layer did not recover significantly, which played an important role in the soil retention function, so the soil retention function basically did not improve. The research showed that soil erosion status variation in TRHR was jointly influenced by rainfall change and ecological engineering, and the ecological consequence of ecological engineering still had local and temporary characteristics. The arduous task of ecological construction should not be ignored.