Monitoring the spatio-temporal dynamics of the wetland vegetation in Poyang Lake by Landsat and MODIS observations

Shaojie Mu; Bing Li; Jing Yao; Guishan Yang; Rongrong Wan; Xibao Xu

doi:10.1016/j.scitotenv.2020.138096

Monitoring the spatio-temporal dynamics of the wetland vegetation in Poyang Lake by Landsat and MODIS observations

Sci Total Environ. 2020 Jul 10:725:138096. doi: 10.1016/j.scitotenv.2020.138096. Epub 2020 Mar 20.

Authors

Shaojie Mu¹, Bing Li¹, Jing Yao¹, Guishan Yang², Rongrong Wan¹, Xibao Xu¹

Affiliations

¹ Key Laboratory of Watershed Geographic Sciences, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, 73 East Beijing Road, Nanjing 210008, PR China.
² Key Laboratory of Watershed Geographic Sciences, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, 73 East Beijing Road, Nanjing 210008, PR China. Electronic address: gsyang@niglas.ac.cn.

PMID: 32302824
DOI: 10.1016/j.scitotenv.2020.138096

Abstract

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 km² year^-1) can be observed during 2001-2009 as compared to that of the overall study period (18.4 km² year^-1). 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.

Keywords: Land cover; NDVI; OBIA; Poyang Lake; Vegetation phenology; Wetland vegetation.

MeSH terms

China
Ecosystem
Environmental Monitoring
Lakes*
Wetlands*