| Wetlands have the reputation of "the earth's kidney" and play an important role in regulating climate,flood control,water storage,protecting biodiversity,and purifying water sources.In recent years,with the global environmental changes and the disturbance of human activities,wetlands around the world are experiencing rapid and large-scale degradation.Wetland protection has becoming a hot issue of worldwide concern.Xiaoxinganling located in the middle temperate zone of China has developed many wetlands and has unique ecological functions.However,for decades,the Xiaoxinganling wetlands have been damaged by a series of production and construction activities such as agricultural reclamation,deforestation,and global environmental changes,which has caused the wetland area decreased rapidly and the wetland ecosystem function was severely damaged.In this paper,wetlands were taken as the research target in Xiaoxing'anling.(1)Using Landsat remote images,herbaceous wetlands,shrub wetlands,forest wetlands with the five periods of 1975,1985,1995,2005,and 2015 in Xiaoxing'anling were extracted,and temporal and spatial changes of three type wetlands were analyzed.(2)The spatio-temporal changes including the temperature,precipitation,ground surface temperature,Normalized Vegetation Index(NDVI)and freeze-thaw thickness of Xiaoxinganling were analyzed from 1975 to 2015(40a),1975 to 1985,1985 to 1995,1995 to 2005 and 2005 to 2015.Meanwhile,the socio-economic characteristics were too analyzed.(3)The Max Ent model was established to quantify the driving factors of wetlands reduction in five different periods,and analyze the relationships between the main driving factors and wetland reduction.Furtherly,Geodetector model was built to explore the impact of factor interactions on wetlands.This study provides scientific basis for the protection of wetlands and has important theoretical significance and application value for the sustainable development and ecological restoration of wetlands.The main results were as follows:(1)From 1975 to 2015(40a),the areas of herbaceous wetlands,shrub wetlands,and forest wetlands decreased sharply in Xiaoxinganling,and three types of wetlands were mainly transformed into forest and cultivated land.From 1975 to 1995,the areas converted from wetlands to cultivated land were on the rise.However,after 1995,the areas converted from wetland to cultivated land decreased.During the entire research period,that cultivated lands were the main transfer type of wetlands proved human reclamation was an important factor for wetland degradation.(2)From 1975 to 2015,the wetlands changed drastically and their stability deteriorated.The intensity of the wetland degradation gradually increased from north to south and west to east.The migration distance of forest wetlands and shrub wetland was larger,relative to herbaceous wetland.The main reason for the migration of the three types of wetlands was caused by the uneven of the degradation of wetlands.There were both common laws and differences between the landscape pattern evolution law of the Xiaoxinganling wetlands and the middle and low latitude natural wetlands.(3)From 1975 to 2015,temperature,ground surface temperature,and precipitation in the Xiaoxinganling showed an upward trend.The spatial characteristics of climatic elements indicated that the rising trend of the temperature in the north and central was higher than in the south,the upward trend of ground surface temperature was the largest in the central,and the northern regions were higher than the southern regions,and the upward trend of the precipitation was strongest in the south,especially southwest,compared with the north.(4)It was a significant downward trend for year and seasonal freeze thawing thickness in the Xiaoxing'anling from 1975 to 2015,and the decline rates were spring(7.87cm/10a)> summer(3.16cm/10a)> winter(1.79cm/10a)> autumn(0.873cm/10a).The spatial distribution of the freeze thawing thickness during 40 years indicated that the decline intensity of the freeze thawing thickness in the south was significantly greater than that in the north,and the decline intensity in the east was greater than that in the west.From 1975 to 2015,there was a significant downward trend for NDVI(p <0.05).NDVI in the northern,central,and southeastern areas of the study area showed a downward trend(p <0.05).(6)The driver factors for the degradation of three type wetlands were different,and the key driver factors of the same type wetland degradation in different interdecadal were different from 1975 to 2015.The driving factors of herbaceous wetland degradation had interdecadal differentiation characteristic.The inflection point of the herbaceous wetland degradation happened in 1995.The expansion of cultivated lands was most key driving force caused herbaceous wetlands degradation befor 1995,however,after 1995,especially after 2005,cultivated lands were no longer the most important driving force for the degradation of herbaceous wetlands.Therefore,the degradation of the herbaceous wetland was dominated by human activities,and was the result of the joint action of human activities and changes in the natural environment in Xiaoxing'anling during 40 years.The degradation of shrub wetlands in different interdecadal was mainly affected by the changes of temperature and freezing thawing hickness,and the degradation of forest wetlands was mainly caused by changes of ground surface temperature,temperature,and freezing thawing thickness.There were south-north and east-west differences in the driving factors for the reduction of wetlands in Xiaoxinganling.The expansion of cultivated land in the south and east was most important factor for the reduction of herbaceous wetlands.Howerver,the reduction of wetlands in the north and west had been affected by changes in natural environmental factors for a long time.Therefore,the reduction of the wetlands in Xiaoxinganling during 40 years was the combined effect of cultivated land expansion and natural environment changes,and had spatial differentiation characteristics.The interaction between the main environmental drivers that led to the degradation of wetlands had further exacerbated the degradation of wetlands. |
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