Key Laboratory of Watershed Geographic Sciences, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, 73 East Beijing Road, Nanjing 210008, PR China.
Key Laboratory of Watershed Geographic Sciences, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, 73 East Beijing Road, Nanjing 210008, PR China.
Sci Total Environ. 2020 Jul 10;725:138096. doi: 10.1016/j.scitotenv.2020.138096. Epub 2020 Mar 20.
Poyang Lake, the largest freshwater lake of China, provides critical ecological functions for water circulation and biodiversity conservation as a dynamic wetland system. However, recent climate change and human activities exerted strong pressures on this ecosystem. In this paper, we applied object-based image analysis (OBIA) and Radom Forests (RF) classifier to ten Landsat images to examine the land cover composition and its change during 1987-2017 low water season at Poyang Lake. NDVI time series (2000-2017) derived from MODIS imagery was used to document the changes of vegetation growth status. To investigate the potential driving mechanism of the inundation patterns, we differentiated the spatial-temporal changes of vegetation coverage and NDVI accumulation on eight elevation bands. Major result indicates that the vegetation area increased by 15.5% of the lake area during 1987-2017. A much faster-increasing rate (58.0 km year) can be observed during 2001-2009 as compared to that of the overall study period (18.4 km year). Analysis of NDVI accumulation showed that 42.1% of the lake's area displayed a significant increasing trend during 2000-2017. Spatially, the increase of vegetation area and NDVI accumulation mainly took place in the 11-12 m elevation band in the lower lake center. Early dry season and prolonged exposure period after the operation of Three Gorges Dam (TGD) was the major reason for the spatio-temporal evolution of the wetland vegetation in Poyang Lake. The Lake's water level started to fall below 12 m before 9th November might cause a boost of vegetation growth in the low lake center, and in turn, triggering xerophilization for the vegetation in the highlands and a shift in foraging patterns of waterbirds due to phenology variations. The findings of this study provide a clear reference for sustaining the inter-annual stability of the ecosystem by controlling the depth of water in the lake.
鄱阳湖是中国最大的淡水湖，作为一个动态湿地系统，为水循环和生物多样性保护提供了关键的生态功能。然而，最近的气候变化和人类活动对这个生态系统施加了强大的压力。在本文中，我们应用基于对象的图像分析（OBIA）和随机森林（RF）分类器，对 1987 年至 2017 年低水位季节的 10 张 Landsat 图像进行了分析，以研究鄱阳湖的土地覆盖组成及其变化。从 MODIS 图像中得出的 NDVI 时间序列（2000-2017 年）被用来记录植被生长状况的变化。为了研究淹没模式的潜在驱动机制，我们区分了植被覆盖和 NDVI 积累在八个高程带的时空变化。主要结果表明，1987 年至 2017 年间，湖区的植被面积增加了 15.5%。与整个研究期间（18.4km 年）相比，2001-2009 年的增长率（58.0km 年）要快得多。NDVI 积累分析表明，2000-2017 年间，湖区有 42.1%的地区呈现出显著的增加趋势。空间上，植被面积和 NDVI 积累的增加主要发生在湖区中心的 11-12 米高程带。三峡工程（TGD）运行后，枯水期提前和暴露期延长是鄱阳湖湿地植被时空演变的主要原因。湖水位在 9 月 11 日之前降至 12 米以下，可能会促进湖区低水位地区的植被生长，进而导致高地地区的植被干旱化和水鸟觅食模式的转变，这是由于物候变化。本研究的结果为通过控制湖泊水深来维持生态系统的年际稳定性提供了明确的参考。
