| The development of cyanobacteria in Chao Lake is influenced by various natural factors and human activities,and has a high degree of spatial and temporal variability and imbalance.Evaluating the temporal and spatial distribution characteristics of cyanobacteria through remote sensing image data is an important basis for analyzing the influencing factors and Control Countermeasures of cyanobacteria in Chaohu Lake.When studying the temporal and spatial distribution characteristics of cyanobacteria bloom,we usually use single band threshold method,multi band spectral relationship method and machine learning method to retrieve the cyanobacteria bloom,and analyze the temporal and spatial distribution of cyanobacteria bloom from the aspects of coverage area,initial outbreak time,duration and main environmental driving factors.On the other hand,Chaohu Lake area has a large number of wetlands and rich natural resources,its landscape pattern changes directly affect the region’s various ecological processes and functions.Therefore,by studying the landscape pattern around Chaohu Lake,we can understand the landscape diversity of the region,and provide important reference for improving the protection and sustainable utilization of ecological landscape.In view of this,this paper takes the cyanobacteria in Chaohu Lake and the landscape around Chaohu Lake as the research object.In order to comprehensively evaluate the temporal and spatial distribution characteristics of cyanobacteria in Chaohu Lake,based on the inversion of cyanobacteria by NDVI,proposes an evaluation method based on the coupling of NDVI mean and Gini coefficient.In order to understand the temporal and spatial changes of the landscape pattern around Chaohu Lake from 2012 to 2021 and its impact on the cyanobacteria in Chaohu Lake,this paper uses a variety of classification methods to compare,selects the method with the highest classification accuracy to extract the landscape information,uses the landscape pattern index to analyze the changes of the landscape pattern around Chaohu Lake,and further selects the typical areas around Chaohu Lake to explore the impact of the landscape pattern on the cyanobacteria in Chaohu Lake.The main conclusions are as follows:(1)A comprehensive evaluation system for the temporal and spatial distribution of cyanobacteria bloom in Chaohu Lake was constructed.In order to quantitatively evaluate the temporal and spatial distribution characteristics of cyanobacteria in Chaohu Lake,a comprehensive evaluation system is proposed,in which the mean value of NDVI is taken as the evaluation index of the overall severity of cyanobacteria and the correlation relationship between "NDVI value and corresponding cyanobacteria quantity" is taken as the evaluation index of equilibrium degree.The comprehensive evaluation results show that the overall severity of cyanobacteria blooms shows a decreasing trend from 2012 to2021,indicating that the overall severity of cyanobacteria blooms in Chaohu Lake has been improved in recent years.The Gini coefficient range of 62 images is [0.02,0.40],and 34 scenes are larger than 0.10,indicating that the uneven distribution of cyanobacteria blooms is more common in Chaohu Lake over the years.The imbalance degree of cyanobacteria varies greatly in different years.(2)This paper reveals the evolution characteristics of landscape types in the 5km area around Chaohu Lake from 2012 to 2021.In order to select the classification method with the best classification effect and extract the landscape pattern information of the 5km area around Chaohu Lake from 2012 to 2021,the classification accuracy of maximum likelihood method,object-oriented single-layer method and object-oriented multi-level method is compared.The results show that compared with maximum likelihood method and object-oriented single-layer method,the overall accuracy of object-oriented multi-level classification method is increased by 10.57% and 1.86% respectively,and the kappa coefficient is increased by 0.13 and 0.02 respectively.The object-oriented multi-level method is used to extract the landscape information of the 5 km area around Chaohu Lake from 2012 to 2021.It is found that dry land accounts for the largest proportion among them.(3)Quantitative analysis of temporal and spatial changes of landscape pattern around Chaohu Lake and its impact on cyanobacteria bloom in Chaohu Lake.In this paper,the landscape pattern index is used to analyze the landscape pattern of the area 5km around Chaohu Lake,and four typical areas 5km around Chaohu Lake are selected to analyze the impact of the proportion of landscape types on the cyanobacteria bloom in Chaohu Lake.The results show that from 2012 to 2021,the landscape types have been decomposed,and the degree of landscape fragmentation has become higher;The landscape diversity index increased,and the distribution of various landscape types tended to be uniform.Buildings and bare land in the 5km area around Chaohu Lake can promote the outbreak of cyanobacteria bloom,and high vegetation coverage can inhibit the outbreak of cyanobacteria bloom.In conclusion,the evaluation method based on NDVI mean and Gini coefficient is helpful to scientifically measure the large-scale temporal and spatial distribution law of cyanobacteria and predict the related risks.The research results can provide decision support for government departments to control cyanobacteria.It can provide a reference basis for ecological planning and ecological protection decision-making around Chaohu Lake. |
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