Remote Sensing Monitoring And Evolution Driving Factors Analysis Of Aquatic Vegetation In Taihu Lake

Aquatic vegetation plays an important role in maintaining the balance of lake ecosystems,of which spatial distribution and dynamic information are the keys and foundation to the steady state research and evaluation of shallow lakes.and foundation to the steady state research and evaluation of shallow lakes.It is of great significance to study the spatial distribution characteristics of aquatic vegetation and to analyze the evolution driving factors to maintain the ecological balance and improve the lake water quality.In this paper,grass-type zone of Taihu Lake was selected as the study area.Using the filed measured data,Landsat-5 and HJ-CCD multispectral satellite remote sensing images of 2016 and 2017,the spectral characteristics of aquatic vegetation groups were analyzed and the sensitive spectral bands of aquatic vegetation groups were determined.Combined with wave bands operation and image enhancement technology,the sensitive spectral characteristic indexes of different groups suitable for satellite imagery monitoring were constructed.Classification decision tree(CT)model which mapping aquatic vegetation groups was established based on Classification and Regression Tree(CRAT)and three spectral characteristic indexs of EVI,FVSI,and SVSI to in turns extract the emergent,floating-leaved and submerged vegetation.By the verification of field survey points,the overall accuracy of CT model for mapping aquatic vegetation were 83.56%and 87.80%respectively.The spatial distribution characteristics of aquatic vegetation in Taihu Lake were studied of 1990,1995,2000,2005,2010 and 2015 by using long time series of Landsat-5 and HJ-CCD data.By the verification of historical field survey samples,the overall accuracy of remote sensing for aquatic vegetation in 1990,1995,2000,2005,2010 and 2015 were 76.39%?73.97%?76.54%?75.00%?76.32%?73.33%,and the Kappa coefficients were 0.68?0.65?0.69?0.66?0.68,0.64?Remote sensing monitoring results show that,in the past 25 years,the distribution area of aquatic vegetation in Taihu Lake increased from 126.78km2 in 1990 to 300.27km2 in 2000 and then decreased to 141.15km2 in 2015;The distribution area of emergent vegetation continuously decreased from 34.59km2 in 1990 to 3.66km2 in 2015.The distribution area of floating-leafed vegetation increased from 28.11 km2 in 1990 to 106.07 km2 in 2010 and then decreased to 66.81 km2 in 2015.The area of submerged vegetation increased from 64.09 km2 in 1990 to 206.77 km2 in 2000 and then decreased to 70.68 km2 in 2015.The analysis of evolution driving factors shows that the evolution of aquatic vegetation were related to the environmental factors of the lake,meteorological factors,land use,social economy,and human factors.Human factors play a major role in the succession of aquatic plants,in which the water eutrophication was the main reason for the reduction of submerged vegetation,and artificial harvesting was the main reason for the reduction of floating-leafed vegetation in Taihu Lake.