关键词: NDVI, 高寒湿地, 黄河源区, 玛曲, 生态格局

Abstract: Wetland as a unique ecosystem has important environment regulating functions and irreplaceable role in maintaining regional ecological balance, conserving biodiversity, and providing food, materials and water resources to humans. The Maqu alpine wetland located in the northeast of the Tibetan Plateau is an important water conserving and supplying area to the upper reach of the Yellow River. In the past 30 years, global warming has led to significant vegetation changes on the Tibetan Plateau. The Maqu alpine wetland is undergoing a process of prominent warming and drying, and degradation of its water conservation function is very significant in recent years. Wetland vegetation dynamics , regional differentiation and causes of degradation of the alpine wetland ecosystem were investigated using multi-source remote sensing data in this study. Land use information and ecological patterns of Maqu were extracted via analyzing Landsat-5/TM and Landsat-7/ETM+ satellite images of 2000 and 2010, through visual interpretation and supervised classification using GIS techniques. NDVI (Normalized Difference Vegetation Index) was used as an indicator in monitoring vegetation changes. MODIS NDVI time series data of 2000-2010(after applying the S-G filtering method and MVC) were used to detect temporal and spatial variations and evolution trend of wetland ecosystems. Point data from weather stations was interpolated using Kriging interpolation method. Based on long-term observations from weather stations，the relationship between Maqu wetland changes and climatic factors(temperature and precipitation) was examined using the least squares method. The results show that areas of rivers, inland beaches, ponds, and swamp meadows were decreasing. Summer NDVI of 2000-2010 in the study area also decreased. Areas with significant decline in NDVI are located in Cairima, Manrima and Hequmachang. Changes in vegetation type also occurred, as signified by swamp meadows shifting to subalpine meadows. The warming and dry climate appears to be a critical factor contributing to the degradation of the Maqu alpine wetland. The changes of the Maqu alpine wetland are related to the inter-annual variability of precipitation and temperature, with 61% and 51% of the total area showing a positive correlation between NDVI and annual precipitation as well as between NDVI and mean temperature respectively. A stronger correlation exists between NDVI and annual precipitation, indicating that the vegetation growth is more sensitive to the inter-annual variability of precipitation.

Key words: alpine wetlands, ecological pattern, Maqu, NDVI, Yellow River Source Area