Analysis On The Spatio-temporal Change Of Wetlands And Its Driving Mechanism In Haikou City During The Past 60 Years

Wetlands with the unique environmental conditions make the wetland have abundant material flow,energy flow and information flow,and also provide a habitat for diverse organisms.It used to be considered as one of the most pr oductive ecosystems in the world.In the context of global climate change and rapid urbanization,Haikou’s wetlands face a series of problems such as sharp decline in quantity,quality degradation,environmental pollution and so on.Bas ed on six-phase remote sensing images(1959,1976,1985,1995,2005 and 2018)and three-phase land use data(1995,2005 and 2017),the vector data of wetla nd in different periods in the city were obtained by means of visual interpretat ion.On this basis,the quantity,spatial-temporal distribution and evolution of w etlan-ds in Haikou were analyzed by using transfer Matrix,landscape pattern in dex and centroid transfer model.At the same time,curve estimation,Markov model and ca-Markov model were used to predict the changing trend of wetlan d in 2031.In view of wetland change,the driving mechanism of wetland chan ge in Haikou was analyzed qualitatively and quantitatively.The main conclusio ns of the paper are as follows:(1)The change of wetland quantity:from 1959 to 2018 the area of total decrease was 19704.36 hm~2,the loss rate was 21.86%.Coastal Wetland,inlan d wetland and constructed wetland decreased by 1970.75,3539.02 and 14194.59hm~2.The annual average wetland area reduction rates for different periods wer e 1976-1985>2005-2018>1985-1995>2018-2031>1959-1976.From the point of v iew of wetland stability,only 51.57%of wetlands in the city maintained their original types from 1959 to 2018.The stability of Sandy Beach and reservoir i s higher,the stability of muddy beach,Mangrove,river and paddy field is mid dle,and the stability of other three-grade wetland is lower.(2)Wetland spatial change:only coastal and coastal wetland spatial change was small from 1959 to 2018.The change of inland wetland can be summed up as"a river on both sides of the river,small losses and big losses",that i s,the small patches of inland wetland on both sides of the Nandu River river disappear and the large patches shrink.The change of constructed wetland can be summed up as"more towns in one city,more towns inside and more tow ns outside".(3)The change of wetland landscape pattern:from 1959 to 2018,the frag mentation of wetland was increased,the complexity of patch shape was mediu m,and the wetland aggregation level and connectivity index were decreased.(4)The change of wetland centroid migration:from 1959 to 2018,the wh ole centroid of wetland moved 914.35 m to the southeast,from 1959(19°52′57.32′′N,110°25′56.39′′E),migration to 2018(19°53′20.92′′N,110°25′50.78′′E).This shows that the disturbance and influence in the northwest direction is str onger than that in the southeast direction.(5)Analysis of 20312018-2031 projections:(1)the curve estimation model ha s a good fitting degree at the level of the first and second grade wetlands.Th e forecast result of the third grade wetland shows that the wetland is further o ccupied by the urbanized construction in 2031.(2)Markov Model predicts that urban expansion in Haikou will continue to take up wetlands in 2031,but at a slower rate than the rate of decline between 2005 and 2018.(3)CA-Markov Model predicts that the total area of wetlands in 2031 is 68,570.32 hm~2,2.63%less than that in 2018.The rate of reduction of inland wetlands and construct ed wetlands has decreased significantly,but the rate of reduction of coastal an d coastal wetlands has increased,which indicates that more and more attention is being paid to wetland conservation,the increase of urban construction land mainly comes from other land use.(4)All Things considered,the CA-Markov model is the most suitable model for forecasting wetland change in Haikou.(5)Driving analysis of wetland change:Qualitative analysis——(1)climatic effect:The temperature increased 0.65°c,the climate experienced a long period of warming and drying in the early stage,and the frequent extreme precipitation events in the near future were unfavorable to the wetland recovery.(2)Socio-economy:urbanization has brought about population concentration,expansion of construction land,pollutionwastewater discharge,extensive production water,etc.,which has compressed wetland planning and aggravated water shortage and uneven spatial and temporal distribution in Haikou..(3)In terms of policy factors:reviewing the Haikou wetland policy,the city’s wetland protection is also the traditional way of"destruction first,recovery later","pollution first,treatment later".After a long period of time from 1959 to 2005,no decision was made to protect and manage wetlands.Only then did some progress be made in wetland protection and restoration.However,the area of natural wetlands showed a decreasing trend.In the quantitative analysis-(1)There is a high correlation between climatic factors and some wetlands in Quantitative analysis,but the correlation level is not high,it indicates that socioeconomic development is the dominant factor of wetland change in Haikou.(2)Principal Component Analysis(PCA)screened out three principal components,the overall variance contribution rate is 87.41%,the first principal component is the socioeconomic factor,is the main factor affecting the change of Haikou Wetland(contribution rate is 60.18%).The second principal component is climatic factor,whose contribution rate is 19.03%.It mainly causes wetland changes through precipitation and evaporation.The third principal component is agricultural production,whose contribution rate is 8.21%.(7)suggestions on wetland conservation:to ease the contradiction between economic development and wetland conservation,it is necessary to do a good job in the long-term"protection battle"of wetland ecology,including:(1)establishing and perfecting the wetland conservation management organization and formulating a long-term mechanism for wetland conservation;To adhere to the scientific management concept of attaching equal importance to the quantity and quality of wetland protection and restoration,and to combine wetland protection and development;(2)To improve wetland management laws and regulations,to strengthen the popularization of wetland science,to support wetland scientific research and to determine the scale of wetland development;(3)To guide the residents to make scientific and rational use of wetlands,and to formulate and implement a mechanism for ecological compensation for wetlands through"substitution and replacement";(4)To strengthen the construction of water resources government Macroeconomic regulation and control and"Sponge Cities";Protecting the water demand of wetlands.