Research On Remote Sensing Monitoring And Risk Pre-warning Of Cyanobacterial Blooms Based On Multi-source Data In Erhai Lake

As the second largest freshwater lake of Yunnan Province,Erhai Lake is the important drinking water source in Dali.In recent decades,with the rapid development of economy,the impact of human activities on Erhai is becoming increasingly prominent.Water quality deterioration and eutrophication led to the occurrence of cyanobacterial blooms and affected the normal ecological function of lakes.So it's the primary task of water environment protection of Erhai Lake to monitoring and risk pre-warning of blooms.In this paper,we studied the spatio-temporal distribution of cyanobacterial blooms from 1999 to 2016 based on multi-source remote sensing data,and analyzed the environment driving factors of blooms,finally constructed risk pre-warning model.The research work completed and the main results of this paper can be summarized as follows:(1)Comparison of cyanobacteria identification methods and consistency analysis of multi-source remote sensing data.We find that VB-FAHhas a high consistency with FAI,and their performance is better than NDVI by analyzing the differences between VB-FAH,FAI and NDVI.And the results of different sensors also have a high linear correlation,so that we can get time series results which are normalized by empirical linear model.(2)Analysis of spatio-temporal characteristics of cyanobacteria blooms in Erhai Lake.The cyanobacterial blooms data from 1992 to 2016 were obtained by RS.The results show that cyanobacterial blooms mainly broke out in small-scale,and large-scale blooms occurred less,with the maximum area of 42km2 in 2006,the longest duration in 2013,and the latest end-time in 2016.The bloom generally occurred in summer and autumn(especially in October and November).Moreover,blooms usually were observed in northern and central regions,while the southern region is less.(3)Analysis of environment driving factors of cyanobacterial blooms in Erhai Lake.Based on the water quality and meteorological data,the environmental factors that related to the cyanobacterial blooms were identified.The results indicate that,when the nutrition satisfies the need for cyanobacteria growth,the short-term meteorological conditions are the key to the occurrence of blooms.High temperature and strong sunshine can promote the cyanobacteria to float to the surface of water and form blooms,and the water flow which affected by wind influences the distribution and diffusion of blooms.(4)Risk pre-warning of cyanobacterial blooms in Erhai Lake.The bloom risk warning model is established considering the water quality and meteorological data.First,evaluating the nutritional status of water quality by using total nitrogen,total phosphorus and chlorophyll content.Second,when the nutritional status meet the conditions of cyanobacterial blooms,assessing the meteorological risk.Third,when the risk probability meets the threshold,further,the high-risk areas can be evaluated by using the flow field data.