| Sichuan wetlands are the most important water sources and conservation areas of the two most important mother rivers,Yangtze River and Yellow River of the Chinese nation,which plays an important role in maintaining ecological security in western China and even the middle and lower reaches of the Yangtze River,promoting national economic and social development,and governing the regional ecological environment.However,Sichuan is an agricultural province with a large population but a small amount of wetland per capita.With the ongoing global change,rapid population growth and social and economic development,wetlands are facing unprecedented threats and interferences.Scientific conservation and rational utilization of wetland resources has become the consensus of the government and all sectors of society.However,how did the landscape pattern of Sichuan wetlands evolve?What are the driving factors?How did wetland protection affect the regional ecological environment quality?Against the background of increasing global changes in the future and increasing social and economic activities,how will Sichuan wetlands respond?These are not clear yet.Based on these,this study takes the entire Sichuan Province wetland as the research object and uses 4 phases of 318 scene Landsat series remote sensing images covering Sichuan Province in 1990,2000,2010 and 2015 as the data source to divide the wetland into natural wetlands(swamps wetlands,river wetlands and lake wetlands)and constructed wetlands(ponds and other constructed wetlands).Using artificial visual methods for interpretation,the provincial wetland spatial database was established from 1990 to 2015;using landscape pattern indexes and centroid migration models,this study analyzed the spatio-temporal variation characteristics of Sichuan wetland landscape.then studied the correlation between wetland type changes and driving factors through CCA analysis,and finally try to reveal the driving force of wetland type changes.Based on the ANN-CA coupling model,a province-wide wetland area simulation system and model is established to predict the wetland landscape pattern of Sichuan Province in 2030.Taking a typical southwest inland river basin an example——the mainstream of Jialing River(Lizhou section)and Guangyuan Nanhe National Wetland Park located in this area,by constructing the Remote Sensing Ecological Index(RSEI),we quantitatively analyze the impact of wetland protection on regional ecological environment quality.The main results obtained are as follows:(1)Characteristics of spatio-temporal dynamic changes of wetland landscape patternThe wetland composition of Sichuan Province is largest proportion by swamp wetlands,followed by river wetlands,artificial wetlands,and lake wetlands with the smallest area.The plateau wetland in northwestern Sichuan is the main distribution area of Sichuan wetlands,and the wetland area accounts for more than 70%of the total wetland area.In the past 25 years,the total area of wetlands in Sichuan has shown a decreasing trend---a total decrease of 29744.84 hm~2,of which,natural wetlands decreased by92994.03 hm~2,while constructed wetlands increased by 63249.19 hm~2.The province's wetland landscape pattern has changed significantly during the study period.At the landscape level,the number of patches increased by 495,the patch density increased by 2.9555,the maximum patch index decreased by 3.5068,the area-weighted average patch fractal dimension decreased by 0.0094,and the Shannon diversity index increased by 0.0811.At the type level,the number of patches in each wetland landscape type generally shows an increasing trend,among them rivers,swamps,reservoirs and lakes increased by 148,181,311 and 5,respectively;from the average patch area,rivers,swamps and lakes decreased by 272.7893,56.5054 and 3.7356,respectively,while ponds increased by 37.7405;from the largest patch index,rivers and lakes increased by 0.9322and 0.3226,and swamps and ponds decreased by 4.9868 and 4.1086,respectively.The spatial structure of the wetland landscape in the province is developing in the direction of fragmentation,regularization and diversification,which is mainly manifested as:the spatially connected natural wetland landscapes(rivers and swamps)have been developed with great intensity into artificial wetland landscapes with obvious plot division,prominent small patch characteristics and regular shapes,making the advantages of natural wetlands continuously weakened.Features are becoming more prominent.In the past 25 years,the wetland landscape centroid of the whole province has shifted to the southeast with an average annual migration distance of 0.34 km,and the position deviation of the centroid was dominated by the swamp and river wetland that occupied the main part of the wetland.(2)Drivers factors of wetland type change based on CCA analysisFrom 2000 to 2015,the changeable area of Sichuan wetlands were 705374 hm~2.Swamps and rivers were the main changeable wetland in each period.The ponds were the most changeable wetland type,while lakes were the most stable.The main types of change were:swamps transformed into non-wetlands,rivers and non-wetlands changed into ponds.The average temperature,GDP and population explained 16.6%,30.7%and 2.1%of changes in wetland types,respectively,while precipitation and average relative humidity can only explain 0.6%and 0.3%,indicating that GDP,average temperature and population were the main driving factors for the change of wetland types in Sichuan Province.However,the driving factors for the change of different wetland types were different.Specifically,as the GDP increases,the amount of swamp wetlands converted to non-wetlands decreases,while the non-wetlands and river wetlands converted into ponds increases;with the increase of average temperature,the area of swamp wetlands converted into non-wetlands increased.The research results showed that the rapid development of society and economy has played a positive role in protecting and increasing the area of Sichuan wetlands,but global warming still leads to the continuous reduction of swamps.Therefore,in the context of global change,strengthening the protection and restoration of swamps will plays an important role in stabilizing Sichuan wetland resources.In addition,the influencing factors of the same type of wetland transformation also changed over time.From 2000 to 2010,the transformation of lakes into swamp wetlands was negatively correlated with precipitation;while between 2010 and 2015,the correlation with precipitation decreased and was positively correlated with temperature;from 2000 to2010,the conversion between lake wetlands and non-wetlands was positively correlated with the number of people,but between 2010 and 2015,the correlation with the number of people decreased and was negatively correlated with precipitation.(3)Wetland landscape prediction based on ANN-CA coupling modelThe results showed that the ANN-CA model has a high accuracy in simulating the changes of wetland landscape patterns,with an overall accuracy of 98.1%;the accuracy of swamps,rivers,lakes and ponds is 71.9%,72.7%,89.0%and 50.0%,respectively.The prediction results of the wetland landscape pattern in Sichuan Province in 2030 showed that the total scale of wetlands in the next 15 years will show a decreasing pattern,decreasing by 57822.54 hm~2;all types of the wetland will be in a decreasing state,the area reduction of swamps,rivers,lakes and ponds is 41180.83 hm~2?9690.46 hm~2?398.64 hm~2and 6552.64 hm~2,respectively.Furthermore,the reduced areas are mainly distributed in the plateau wetlands in the northwestern part of Sichuan Province,the total amount of wetlands in the Sichuan Basin and the southwestern Sichuan has changed little.These results showed that in the next 15 years,we should strengthen the protection of swamp wetlands in the plateau wetlands to slow down the wetland degradation in the northwestern part of Sichuan Province.(4)Impacts of wetland protection on regional ecological environmentFrom 2000 to 2015,the mean value of RSEI of the study area increased from 0.6378to 0.6388,with an increase of 0.16%.During the 15 years,34.66%of the regional eco-environmental quality has been improved,while 24.42%degenerated.The ecological quality improved area was mainly located in the mountain afforestation area along the two banks of the Jialing River,while the deteriorated area was in the Lizhou urban along the two banks of the Jialing River,where are greatly affected by urbanization.Although the Nanhe National Wetland Park is located in the overall ecological deteriorated area of the study area,the quality of the ecological environment has improved more obviously.Compared with the before construction,the mean value of RSEI increase rate of the wetland park was 109 times higher than the study area.A total of 55.29%of the regional ecology has been improved,while 19.41%degenerated.The ecological quality improved area was mainly located in forest and water areas,while deteriorated area was in the the construction areas,such as roads,squares and venues.Our results showed that the construction of wetland parks plays an important role in protecting the regional eco-environment quality.In conclusion,From 1990 to 2015,Sichuan natural wetlands decreased,while constructed wetlands increased,the total area of wetlands has shown a decreasing trend;The spatial structure of wetland landscape changed to fragmentation,regularization and diversification.GDP,average temperature and population were the main driving factors for the change of wetland types.The construction of wetland parks plays an important role in protecting the regional eco-environment quality,The total area and all types of the wetland will show a decreasing trend in the next 15 years. |
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