| Despite their small size,small and micro wetlands are widely distributed and are of great importance to biodiversity conservation,improvement of the surrounding living environment and climate regulation.In recent years,governments at all levels and the public have been paying more and more attention to small and micro wetlands,but there has been less research on the spatial and temporal evolution characteristics and influencing factors of small and micro wetlands.Therefore,the study on the long-term dynamic evolution of small and micro wetlands and its influencing factors is not only conducive to the protection and utilization of micro-wetland,but also to sponge city construction and rural revitalization.Based on long time series remote sensing images,this study used MNDWI index,NDVI index,support vector machine classification and artificial visual interpretation to extract the spatial information of natural small and micro wetlands(hereinafter referred to as small and micro wetlands)in Wuxi City from 1985 to 2020.The spatial and temporal evolution characteristics of small and micro wetlands in Wuxi City in recent 35 years were discussed from the aspects of dynamic change,transfer matrix,centroid transfer and landscape pattern index.CA-Markov model,In VEST model and geographic detector model were used to study the change of land use type,habitat quality changes and driving factors in Wuxi City,and the possible influence of natural factors and human activities on the evolution of small and micro wetlands in Wuxi City was revealed.The main research conclusions are as follows:(1)In recent 35 years,the total area and number of small and micro wetlands in Wuxi have both increased,with the total area increased from 4349.59 hm~2in 1985 to 10,841.59 hm~2in 2020,an increase of nearly 1.5 times,while the number of small and micro wetlands increased by nearly 1.7 times.The proportion of the total area of natural wetlands increased from 5%in 1985to 12%in 2020.In terms of spatial distribution,Wuxi’s small and micro wetlands are mainly located in Yixing City,which has 34%of the small and micro wetlands area in Wuxi.The small and micro wetlands in Wuxi City have obvious seasonal characteristics,the number of seasonal small and micro wetlands is more,and the number of near-permanent small and micro wetlands is less.The area of small and micro wetlands in Wuxi was mainly 0.1-1 hm~2and 1-3 hm~2,accounting for 36%and 33%of all micro and small wetlands respectively.(2)The results of the landscape pattern indices show that the overall landscape of Wuxi is becoming less aggregated,less connected and more fragmented;the number of patches(NP),patch density(PD),maximum patch index(LPI),edge density(ED)and shape index(LSI)values for natural small and micro wetland landscape types have shown an increasing trend in the last 35years,indicating that the patch structure of micro and wetland is becoming more complex and fragmented.Based on the CA-Markov model,the spreading index(CONTAG),Shannon diversity index(SHDI)and aggregation index(AI)values in Wuxi are predicted to decrease and the scattering and juxtaposition index(IJI)values to increase in 2030,indicating a possible loss of equilibrium,a further decrease in connectivity and a further increase in fragmentation within the overall landscape of Wuxi in the future.(3)Over the past 35 years,land use changes in Wuxi have been characterised by significant urbanisation,as evidenced by a significant increase in the area of urban and rural construction land,which has increased by nearly 2.3 times.In the whole city,4,839.09 hm~2of small and micro wetlands flowed out,of which about 61%were converted into urban and rural construction land;while the main source of inflow of small and micro wetlands is arable land,accounting for about52%of the total inflow area,followed by waters and larger natural wetlands,at 16%and 13%respectively.It is predicted that the total area of wetlands in Wuxi will be further reduced by 12%in 2030 compared with that in 2020,of which 57%will flow out to cultivated land and 35%will flow out to urban and rural construction land.(4)In Wuxi,the habitat quality was mainly general,accounting for 48.54%of the total land area.In general,the habitat quality showed a trend of increasing first and then decreasing,especially after 2005,the overall habitat quality decreased significantly.In the past 35 years,the habitat quality grade in Wuxi City was mainly transformed from average grade,good grade to poor grade,with a range of 70.75%and 10.01%,respectively.The overall spatial distribution of habitat degradation in Wuxi is high in the north and low in the south,and the overall habitat degradation was continuously increasing and the degradation level is increasing,among which89.45%of the slightly degraded grade area is transformed into mild degradation,71.69%of the mildly degraded grade area is transformed into moderate degradation,and 68.06%of the area of moderate degradation grade was transformed into highly degraded area.(5)The distribution of small and micro wetlands in Wuxi is mainly influenced by combination of natural factors and human activities,including average annual temperature,average annual precipitation,GDP and distance from main roads.The interaction among the influencing factors is nonlinear enhancement and two-factor enhancement.Before 2010,natural factors were the main influencing factors of wetland change,among which average annual temperature was the most significant(q>0.04);After 2010,the role of anthropogenic factors increased.It shows that human activities have more and more strong influence on small and micro wetlands.This study has certain reference value for revealing the spatio-temporal evolution characteristics of small and micro wetlands and deepening the cognition of their driving factors,and can provide guidance for the subsequent conservation and sustainable management of small and micro wetlands in the future. |
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