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．