| Wetlands are essential for human survival and the sustainability of the global environment because they offer a wide range of essential ecosystem services for human well-being.However,wetlands are alarmingly degrading and disappearing globally as a result of numerous factors including climate change,pollution,and reclamation.Contrary to wetland mapping and area change monitoring,which are actively conducted on a large scale or even globally,current studies on the ecological status of wetlands and their change evaluation typically concentrate on one or a few specific wetlands,and there are only a small number of assessment studies exploring their change patterns and characteristics on a large-scale region.Uncertainty exists regarding the long-term patterns and factors influencing changes in the ecological status of Ramsar sites,which are chosen as distinctive and typical ecologically important places on a worldwide scale.An important foundation for the creation of realistic conservation strategies and sustainable management is the ongoing monitoring and change evaluation of the biological status of nationally Ramsar sites.In order to study the longterm ecological change trends and characteristics of various types of Ramsar sites covering national scales with different basic ecological environments,and to analyze the natural and anthropogenic factors affecting their ecological condition changes,this study proposes an efficient and highly scalable rapid wetland ecological assessment method applicable to Ramsar sites in China.This study creates a remote sensing ecological indicator dataset covering Ramsar sites in China and inter-scale wetlands from 1986 to 2021 using Landsat images.Seven remote sensing ecological indicators are jointly constructed from two aspects of vegetation health and hydrological dynamics,and a 30-meter interannual scale longtime series wetland remote sensing ecological indicator dataset covering China’s Ramsar sites from 1986 to 2021 is constructed.Interannual time series can be analyzed for trends in ecological conditions using a combination of the Sen algorithm and the MK test.The ecological index dataset is analyzed in this way to check for mutation spots and segment fitting using the Breakout Detection method.Using this method,we may investigate how the ecological status of China’s Ramsar sites has changed over the past few years,with a focus on areas that have recently seen significant ecological disturbance or policy adjustment.The technique may also disclose the geographical and temporal characteristics and patterns of ecological condition changes across and within different wetland divisions in China’s Ramsar sites from 1986 to 2021.With the help of long time series ECMWF-ERA5 meteorological reanalysis data and the extracted data set of internal floor area of each wetland,we use Pearson correlation analysis to examine the impact of natural and human factors on wetland ecological condition changes.The main findings of this study are as follows:(1)From 1986 to 2021,the vegetation quality of Ramsar sites in China demonstrated long-term changes that were mostly stable with local damage features.Vegetation cover increased in 70.7% of Ramsar sites across the country,and the health status of vegetation in 93.1% of Ramsar sites improved.However,the changes in hydrological indicators revealed a trend of aridification in most of China’s Ramsar sites between 1986 and 2021.The Ramsar sites with permanent water and seasonal water coverage decreased by 55.6% and 56.9%,respectively,across the country.The coastal area was the most concentrated region of permanent water reduction in Ramsar sites,and the loss of seasonal wetlands in eastern China’s Ramsar sites was more severe.While certain wetlands around the Yellow River,the middle and lower sections of the Yangtze River,the Qinghai-Tibet Plateau,and the northeastern part of China had a rise in average wetness,72.4% of Ramsar sites exhibited a drop in remote sensing wetness.(2)Currently,70.7% and 82.8% of Ramsar sites in China show an increasing trend in vegetation coverage and vegetation health indicators,respectively.The northeastern region and the middle and lower reaches of the Yangtze River are the regions with the trend of vegetation ecological status of Ramsar sites.Over half of the Ramsar sites are still facing the threat of water shrinkage and decreased wetness.Ramsar sites with permanent water coverage decrease,seasonal water coverage decreases,and remote sensing wetness decrease are 59.3%,56.9%,and 62.1%,respectively.All vegetation and hydrological ecological indicators are highly volatile during long-term changes.The seven vegetation and hydrological ecological indicators of Ramsar sites in China have strong fluctuations in their long-term changes,and more than 50% of Ramsar sites have trend reversal points for all indicators.Overall,the change in hydrological ecological indicators is more significant than vegetation ecological indicators.seasonal water cover is the ecological indicator with the highest proportion of trend reversal points in the long-term change process.(3)In general,there is no correlation between climatic variables and changes in ecological state indicators of Ramsar sites in China.Only 0.65% and 0.33% of the ecological state indicators of Ramsar sites in China shown substantial positive and negative associations in the correlation study with 25 natural components,respectively.The key correlation indicators were summer,autumn,and year average temperature,and most of the vegetation ecological indicators had a high positive connection with temperature.Particularly seasonal wetlands,which are greatly impacted by precipitation,show a substantial positive association between the hydrological ecological indicators and precipitation.With a high positive association for 5.2% of the ecological state indicators and a negative correlation for 6.3%,the intensity of human activities also had varying impacts in various wetlands of worldwide significance.Wetland restoration is significantly influenced by national macro-policies and restoration initiatives.This study provides a practical and reproducible strategy for large-scale wetland ecological assessment,which can be extended to larger areas or global studies with the support of multiple data sources in the future.Adjusting the indicators within the remote sensing evaluation framework can better adapt to large-scale studies according to the ecological characteristics of different regions.Moreover,further analysis of wetland changes drivers after segmenting the ecological indicator curve can better explore and solve regional ecological problems. |
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