太湖湿地植被时空变化特征及其驱动机制

基于1980—2019年Landsat长时间序列遥感影像，结合近40 a的水文和气象数据，综合最大似然、空间质心模型、小波连续变换等方法，分析了太湖水生植被时空变化特征及水位周期变化的影响．结果表明:1）近40 a来太湖水生植被总面积呈现出先减少、后大幅增加、又小幅减少的趋势，动态相对指标为217.50%．沉水植物在总植被面积中占比最大，并在2014年达到峰值340.59 km2；浮水植物面积波动较明显，波动范围为1.32%~19.74%；2014年挺水植物面积达到最低值，为13.35 km2，面积整体上呈下降趋势．2）1980—2019年，太湖水生植被群落空间分布向湖区西北部偏移，挺水植物、浮水植物、沉水植物空间质心整体向湖区西北方向分别移动11.45、25.19、7.01 km，偏移方向分别为北偏西39.74°、6.32°、69.88°．3）近40 a来太湖年均水位呈上升趋势，水位变化的主周期为28 a，经历2次丰枯转换，今后将逐渐进入丰水期；年降雨量、年均温、年日照时间也发生了一定的波动．4）太湖水位周期变化对于水生植被影响较为明显，沉水植物面积与年均水位有显著的正相关性，气象因子与植被面积变化相关性较弱，但是风向对于水生植被迁移影响较大，除此之外人类活动也是影响太湖水生植被时空分布的重要因素．研究结果可为湖泊湿地生态系统、水生植被时空动态及其驱动机制研究提供一定的理论和方法参考，对于太湖湿地生态恢复提供一定的决策支持． 

Temporal and spatial variations in vegetation in Taihu wetland and driving mechanisms

Aquatic vegetation, the primary producer of Taihu wetland ecosystem, plays a key role in the improvement of water quality and internal nutrient cycle in the Taihu Lake ecosystem．Temporal and spatial variations in aquatic vegetation in Taihu wetland and driving mechanisms need to be clarified for logical restoration and protection of the lake ecosystem．Landsat images from 1980 to 2019, hydrological and meteorological data were studied to resolve the temporal and spatial variations in aquatic vegetation; periodic changes in water level in Taihu Lake were analyzed using maximum likelihood, spatial centroid model and wavelet continuous transformation．Total area of aquatic vegetation in Taihu Lake was found in the past 40 years to initially decrease, then increase, before a slight decrease, with a dynamic relative index of 217.50%．Submerged macrophytes were found to account for most of total vegetation area, reaching a peak at 340.59 km2 in 2014．The area of floating plants was found to fluctuate markedly from 1.32% -19.74%．Area of emergent plants reached the lowest value at 13.35 km2 in 2014, with an overall downward trend．The spatial distribution of aquatic vegetation communities in Taihu Lake shifted from 1980 to 2019 to the northwest part of the lake, the spatial centroids of emergent plants, floating plants and submerged plants moved 11.45 km, 25.19 km and 7.01 km to the northwest part of the lake, respectively, with migration directions at 39.74°, 6.32° and 69.88° respectively．The average annual water level at Taihu Lake has showed a rising trend in the past 40 years, the main period of water level change was found to be 28 years．Two periods of abundant and dry changes were identified; gradual entry to a period of abundant water is predicted for the future．Annual rainfall, average annual temperature and annual sunshine hours were found to all fluctuate．The periodic change in water levels in Taihu Lake had marked impact on aquatic vegetation, with a significant positive correlation between area of submerged plants and average annual water level．The correlation between meteorological factors and vegetation area was weak, but wind direction was found to greatly influence migration of aquatic vegetation．Human activity was an important factor in the temporal and spatial distribution of aquatic vegetation in Taihu Lake．These data are significant for the study of temporal and spatial dynamics and driving mechanism of aquatic vegetation in lake wetland ecosystem, and for decision making in the ecological restoration of Taihu wetland．