Remote Sensing Monitoring Of Aquatic Vegetation Groups In Lake Hongze Based On Phenological Characteristics

Aquatic vegetation are not only an important part of the lake water ecosystem,but also a crucial indicator of lake water environment change.Therefore,analyzing the spatial distribution characteristics of aquatic vegetation and the driving factors of their change have big guiding significance for improving the ecological environment of lakes.At present,the main means of obtaining the status of aquatic vegetation distribution is the traditional field sample survey.The results are relatively accurate but the field sample survey is so time-consuming and laborious,it is difficult to obtain continuous spatial distribution information of aquatic vegetation.Satellite remote sensing is time-sensitive,extensive and repeated that can obtain spatial distribution information of aquatic vegetation easily and fast.If remote sensing monitoring methods of aquatic vegetation are constructed,aquatic vegetation spatial distribution and historical imformation can be quickly reconstructed with historical data.This paper attempts to construct a remote sensing classification algorithm for aquatic vegetation groups based on phenological characteristics of Lake Hongze,the fourth largest lake in China.Then the temporal and spatial distribution information of long-time aquatic vegetation in Lake Hongze is reconstructed from the interannual scale.Finaly,making a brief analysis of the changing mechanisms of aquatic vegetation by natural and human factors with meteorological,land use and other auxiliary data.The results show that:(1)The classification accuracy of aquatic vegetation group based on phenological characteristics is 86.36%and the Kappa coefficient is 79.54%.The classification accuracy of floating leaf/emergent vegetation and submerged vegetation is 86.11%and 84.62%respectively.(2)The spatial and temporal distribution characteristics of aquatic vegetation in Lake Hongze are:floating leaf/emergent vegetation is generally distributed on lakeside and beach,and submerged vegetation is distributed in shallow lake area,the aquatic vegetation of Lake Hongze has the highest frequency in the Sihong Wetland Reserve,west district and the Chengzi Lake in the north.(3)On the interannual scale,the distribution area of two types of aquatic vegetation during the period of 2002-2017 both showed a significant downward trend.The area of submerged vegetation decreased from 305.13km~2 in 2002 to 185.31km~2 in2017,with a decreasing ratio of 39.27%;the area of floating leaf/emergent vegetation decreased from 353.26km~2 in 2002 to 184.36km~2 in 2017,the decline ratio was 47.81%;(4)Meteorological factors have little effect on the temporal and spatial variation of aquatic vegetation in Lake Hongze;human activities such as purse seine culture,sand mining and unreasonable land use play an important role in the historical evolution of aquatic vegetation in Lake Hongze on an interannual scale effect.