近50a长江黄河源区生态与环境变化综合研究

本论文主要从宏观尺度分析了近50a长江黄河源区冰川、冻土、积雪、湿地、植被的动态变化过程与特征，并在此基础上使用分布式水热耦合模型(DWHC)对长江源区典型高寒山区小流域水文过程进行了模拟研究。使用主成分分析法评价了江河源区生态环境的脆弱性，基于评价结果，确定了江河源区各分区生态环境变化的主导因子，并就各区存在的生态与环境问题进行了驱动力分析。 　　1江河源区气候与环境变化研究 　　根据行政与地貌单元的完整性；生态环境构成中主成分的趋同性；源区对生态环境体系的包容性；地理与水文源区的同一性四大原则，在综合分析基础上，对长江黄河源生态与环境研究范围进行了科学界定，界定出黄河流域生态与环境研究的源区以达日水文站为界，流域控制面积约4.49×104km2；长江河源区以聂恰曲汇合口为界，流域控制面积约12.24×104km2。 　　对江河源区近50a气候变化的研究表明，近50a江河源区气温显著变暖，两地年平均气温分别增加约0.8℃和0.7℃。与全球、全国以及青藏高原不同，江河源区变暖是四季均变暖的结果。近50a来江河源区降水量略有增加，但降水量的增加主要体现在20世纪80年代中后期以来春季与冬季降水量的明显增加上，夏季降水量总体上没有明显变化。 　　过去50a江河源区冰冻圈变化显著。长江源各拉丹冬地区1969～2000年冰川总面积减少了1.7﹪，而黄河源阿尼玛卿山地区冰川面积减少了17.3﹪。在冰川长期退缩的总趋势下，存在阶段性变化，长江源区在1969年至1995年，黄河源区在1966年至1981年，大多数冰川处于前进状态或稳定。长江源区冰川转入退缩阶段的时间要比黄河源区晚约10a左右。冰川退缩使江源区和河源区年均各自损失冰川水资源约0.7亿m3。近20年来，江河源区岛状多年冻土和季节冻土区年均地温升高约0.3～0.7℃，大片连续多年冻土区升幅较小，为0.1～0.4℃。长江源区冻土退化程度小于黄河源区。近40年江河源区平均冬春累积积雪深度增加了61.0﹪，其中长江源区增长了约62.1﹪，黄河源区约60.2﹪，两源区积雪变化具有自身特征。在江河源区，影响积雪变化的因子有气温、降水量、地温等，但积雪与影响因子间的相关关系具有显著的地域性。 　　2植被生态系统与水文变化研究 　　近20年江河源区高寒湿地数量与面积显著减少。1986到2000年间，长江源区湖泊湿地减少了18.1﹪，水域面积萎缩了10.6﹪，而黄河源区河流湿地数量和面积分别减少了15.8﹪和9.0﹪。反映在河川径流变化过程上，长江源区流量减少约12.4﹪，黄河源区减少约19.0﹪。江河源区沼泽湿地分布面积锐减24.4﹪，其中，长江源区减少28.1﹪，黄河源区减少了13.4﹪。湿草甸减少主要发生在长江源区，减少了27.6﹪，黄河源区减少较少，为7.5﹪。长江源区泥炭沼泽减少了34.9﹪，黄河源区减少了44.2﹪。 　　NDVI植被指数记录的长江黄河源区过去20年植被覆盖整体变化较小，局部显著恶化。年NDVI变化表现出显著的空间差异性。在长江源区的布曲、托托河、楚玛尔河、昂日曲、通天河等流域部分地段与黄河源区的星宿海地区和达日县南部地区，年NDVI为增加区域，变化率为12.86﹪～27.22﹪。在长江源区的托托河沿至伍道梁之间的青藏公路两侧一定范围、曲麻莱和治多一带、黄河源区的扎陵湖和鄂陵湖周边及其北东部地区、巴颜喀拉山北麓的多曲源头地区，年NDVI为较显著减少区域，变化率为-12.5﹪～-56.0﹪。江河源区植被覆盖状况的好坏主要受温度，尤其是40cm附近地温的影响。在江河源多年冻土区，冻土的退化将会直接影响该区植被的生长。 　　长江源区冬克玛底河流域典型草地生态系统变化的研究表明，该流域高寒草甸植被变化主要表现为藏嵩草沼泽化草甸的退化，这种退化是以种群和生境变化为可见标志，以优势种群的变化为主要特征。原生草甸群落发生退化后，群落物种组成与结构发生巨大变化，植被覆盖度由95.4﹪大幅降低为38.8﹪，相同样方地上生物生产量由15.1g减少到6.1g，但群落物种多样性增高。 　　对长江源区冬克玛底河流域2005年6～9月份的日平均流量进行了水文过程模拟研究，模拟结果相对较好。模型的效率系数为0.55，平衡误差为4.05﹪，解释方差为0.56。研究表明了严寒气候与多年冻土条件决定了流域浅表产流特性；高山草甸具有拦蓄作用和水源涵养功能，其生态功能更大于其水文功能。

This paper mainly analyzes the dynamic processes and characteristics of glaciers, frozen soil, snow cover, wetlands and vegetation in the source regions of the Yangtze and Yellow Rivers over the past 50 years at a macro scale. On this basis, the Distributed Water-Heat Coupling Model (DWHC) was used to simulate the hydrological processes of a typical alpine mountainous small watershed in the source region of the Yangtze River. The Principal Component Analysis (PCA) was employed to evaluate the ecological environment vulnerability of the source regions of the two rivers, and based on the evaluation results, the dominant factors driving ecological and environmental changes in each sub-region of the source areas were identified, followed by a driving force analysis of the ecological and environmental issues existing in each sub-region.

1 Research on Climate and Environmental Changes in the Source Regions of the Yangtze and Yellow Rivers
Based on four principles: the integrity of administrative and geomorphic units, the convergence of principal components in the ecological environment composition, the inclusiveness of the source regions to the ecological environment system, and the identity of geographical and hydrological source regions, the research scope of the ecological environment in the source regions of the Yangtze and Yellow Rivers was scientifically defined. The source region of the Yellow River basin for ecological and environmental research is bounded by the Dari Hydrological Station, with a controlled watershed area of approximately 4.49×10^4 km²; the source region of the Yangtze River is bounded by the confluence of the Nieqiaqu River, with a controlled watershed area of approximately 12.24×10^4 km².

Studies on climate change in the source regions of the two rivers over the past 50 years show that the temperature has warmed significantly, with the annual average temperature increasing by approximately 0.8°C and 0.7°C respectively in the two source regions. Unlike the global, national and Qinghai-Tibet Plateau warming trends, the warming in the source regions of the two rivers is the result of warming across all four seasons. The precipitation in the source regions has slightly increased over the past 50 years, but the increase is mainly reflected in the significant increase in spring and winter precipitation since the mid-to-late 1980s, while the summer precipitation has not shown an overall significant change.

The cryosphere in the source regions of the two rivers has changed significantly over the past 50 years. The total glacier area in the Geladandong region of the Yangtze River source decreased by 1.7% from 1969 to 2000, while that in the Anyemaqen Mountains region of the Yellow River source decreased by 17.3%. Under the overall trend of long-term glacier retreat, there are periodic changes: most glaciers were in an advancing or stable state in the Yangtze River source region from 1969 to 1995, and in the Yellow River source region from 1966 to 1981. The timing of the shift to the retreat phase for glaciers in the Yangtze River source region is approximately 10 years later than that in the Yellow River source region. Glacier retreat caused the Yangtze and Yellow River source regions to lose approximately 70 million m³ of glacial water resources annually each. In the past 20 years, the annual average ground temperature in the island-shaped permafrost and seasonally frozen soil areas of the two source regions has increased by approximately 0.3–0.7°C, while the increase in large continuous permafrost areas is smaller, at 0.1–0.4°C. The degree of permafrost degradation in the Yangtze River source region is less than that in the Yellow River source region. The average cumulative snow depth in winter and spring in the two source regions has increased by 61.0% over the past 40 years, with the Yangtze River source region increasing by approximately 62.1% and the Yellow River source region by approximately 60.2%; the snow cover changes in the two source regions have their own characteristics. In the source regions of the two rivers, factors affecting snow cover changes include air temperature, precipitation, ground temperature, etc., but the correlation between snow cover and these influencing factors shows significant regional differences.

2 Research on Vegetation Ecosystem and Hydrological Changes
The number and area of alpine wetlands in the source regions of the two rivers have decreased significantly over the past 20 years. From 1986 to 2000, the lake wetlands in the Yangtze River source region decreased by 18.1%, and the water area shrank by 10.6%, while the number and area of river wetlands in the Yellow River source region decreased by 15.8% and 9.0% respectively. Reflecting in the changes of river runoff, the runoff in the Yangtze River source region decreased by approximately 12.4%, and that in the Yellow River source region decreased by approximately 19.0%. The distribution area of marsh wetlands in the source regions of the two rivers has sharply decreased by 24.4%, with the Yangtze River source region decreasing by 28.1% and the Yellow River source region by 13.4%. The reduction of wet meadows mainly occurred in the Yangtze River source region, with a decrease of 27.6%, while the Yellow River source region had a smaller decrease of 7.5%. The peat marshes in the Yangtze River source region decreased by 34.9%, and those in the Yellow River source region decreased by 44.2%.

The overall change in vegetation cover in the source regions of the Yangtze and Yellow Rivers over the past 20 years, as recorded by the Normalized Difference Vegetation Index (NDVI), was small, but there was significant local deterioration. The annual NDVI changes show significant spatial differences. In some sections of the Buqu, Tuotuohe, Chumarhe, Angriqu and Tongtian river basins in the Yangtze River source region, and in the Xingxiu Lake area and southern Dari County in the Yellow River source region, the annual NDVI increased, with a change rate of 12.86%–27.22%. In certain areas along both sides of the Qinghai-Tibet Highway between Tuotuohe and Wudaoliang in the Yangtze River source region, the areas around Qumarlêb and Zhidoi, the areas around and northeast of Zhaling Lake and Eling Lake in the Yellow River source region, and the source area of the Duoqu River at the northern foot of the Bayan Har Mountains, the annual NDVI decreased significantly, with a change rate of -12.5%–-56.0%. The status of vegetation cover in the source regions of the two rivers is mainly affected by temperature, especially the ground temperature around 40 cm. In the permafrost areas of the source regions of the two rivers, permafrost degradation will directly affect the growth of local vegetation.

Studies on the changes of typical grassland ecosystems in the Dongkemadi River Basin of the Yangtze River source region show that the changes of alpine meadow vegetation in this basin are mainly manifested as the degradation of Kobresia tibetica swamp meadow. This degradation is marked by visible changes in populations and habitats, with the changes in dominant populations as the main feature. After the degradation of the original meadow community, the species composition and structure of the community have undergone tremendous changes: the vegetation coverage has dropped sharply from 95.4% to 38.8%, and the above-ground biomass production in the same quadrat has decreased from 15.1 g to 6.1 g, but the community species diversity has increased.

Hydrological process simulation was conducted on the daily average flow from June to September 2005 in the Dongkemadi River Basin of the Yangtze River source region, and the simulation results were relatively good. The model efficiency coefficient was 0.55, the equilibrium error was 4.05%, and the explained variance was 0.56. The research indicates that the cold climate and permafrost conditions determine the surface runoff generation characteristics of the watershed; alpine meadows have water retention and conservation functions, and their ecological functions are greater than their hydrological functions.