三江源区生态系统状况变化及其成因

三江源区是黄河、长江和澜沧江的发源地.为研究三江源区生态系统状况变化及其可能成因，利用InVEST（Integrate Valuation of Ecosystem Services and Tradeoffs）、CASA（Carnegie-Ames-Stanford Approach）、RUSLE（Revised Universal Soil Loss Equation）和RWSQ（Revised Wind Erosion Equation）模型模拟，结合实地观测数据，系统全面地评估2000年以来三江源区生态系统构成、质量和服务功能变化，并揭示其成因.结果表明:① 2000—2010年三江源区生态系统结构基本稳定.草地退化状况轻微好转，产草量和生产力微弱增加.植被生长季水热条件的改善是促使产草量增加和草地退化态势趋缓的重要原因，同时生态工程的实施也发挥了积极作用.② 2005—2010年局部重点生态工程区的水土流失状况轻微好转，但区域整体好转趋势不明显.土壤中w（有机质）明显增加，但对于土壤保持功能起到关键作用的植被根系层的恢复却比较缓慢，降雨侵蚀力的增强加速了土壤侵蚀过程，生态系统的土壤保持功能基本上没有提高.③ 2000—2013年地表水、地下水资源量和土壤湿度均呈明显增加趋势，水质稳定在GB 3838—2002《地表水环境质量标准》划定的Ⅰ~Ⅱ类.降水量和冰川/积雪融水量增加导致径流量增大，气候变暖引起的冻土退化导致地下水库枯水季径流调节作用增强.④ 生态工程实施后，生物栖息地的生境退化状况轻微改善，野生动物的分布范围和种群数量都有了较为明显的增加. 

Ecosystem Status Changes and Attribution in the Three-River Headwaters Region

The Three-River Headwaters Region (TRHR) is located in the hinterland of the Qinghai-Tibet Plateau, China, and is the source area of the Yangtze River Basin (YARB), the Yellow River Basin (YRB) and the Lancang River Basin (LRB). TRHR is an important component of the ecological barrier of China, which is related to national ecological security and long-term development.In order to investigate the ecosystem structure, quality and ecosystem service changes, observation data and model simulation results, including Integrate Valuation of Ecosystem Services and Tradeoffs (InVEST), Carnegie-Ames-Stanford Approach (CASA), Revised Universal Soil Loss Equation (RUSLE) and Revised Wind Erosion Equation (RWSQ), were combined to quantitatively assess the spatial pattern of ecosystem types and ecosystem service change since 2000, and then to understand and reveal the causes of the ecosystem health status.The main conclusions are as follows:(1) During 2000-2010, the ecosystem structure in TRHR was basically stable; the farmland and desert area decreased, and urban land and wetland slightly increased. The vegetation coverage increased in more than 65% of the area of TRHR, and the grassland degradation trend improved to a certain extent, but the overall degradation pattern did not show fundamental changes. The carbon sequestration in TRHR and sub-regions increased slightly, which was more obvious in the northern part of YRB and Qinghai Lake Basin. The temperature and rainfall increment jointly promoted Net Primary Productivity (NPP) and grass yield significantly, and ecological engineering also play a positive role. (2) After the implementation of ecological engineering in 2005, the soil loss status in key project areas improved, but the overall improvement trend was not significant.The soil organic matter obviously improved during 2005-2010, but the root layer restoration of vegetation is a slow process, and the rainfall erosivity increment also enhanced the soil erosion process, so the ecosystem's soil conservation function was basically not improved. (3) Over the period 2000-2013, surface water, groundwater and soil water resources in TRHR showed a significant increasing trend. The water quality stabilized at class Ⅰ-Ⅱ as classified by Environmental Quality Standards for Surface Water (GB 3838-2002), indicating basically no change. The increment in precipitation and ice/snow melting water led to stream flow increase, and permafrost degradation induced by regional warming resulted in enhancement in runoff regulation effect of underground reservoir in the dry season. (4) The wildlife habitat degradation conditions were slightly improved; the population of wild animals and distribution range increased significantly, such as Alpine Musk Deer, White-lipped Deer and Eastern Elk. The ecological engineering since 2005 effectively improved the grassland degradation and soil loss, and wildlife habitat developed in a positive direction.However, the ecological status change was also influenced by climate change, and the ecological consequence of ecological engineering still has local and temporary characteristics. Besides, grassland rodents and other factors threatening healthy grassland development still exist; the arduous task of ecological construction should not be ignored.