Evolution Pattern Of Salinization In Modern Yellow River Delta And Its Response Mechanism To Climate-human Interaction

As one of the important components of ecosystem,soil had an important influence on promoting the function of ecosystem and maintaining structural stability.Soil salinization directly or indirectly affected the development and utilization of land resources.As one of the three major estuary deltas in China,the Yellow River Delta（YRD）had the youngest,most complete and broadest new wetland ecosystem in the warm temperate zone of China.However,due to the influence of natural and human activities such as sea-land interaction,seawater intrusion,changes in soil salinity,unreasonable reclamation,unreasonable irrigation,and unreasonable application of chemical fertilizers,the ecosystem had been seriously damaged and the salinization situation is extremely severe.Most of the previous studies are based on two-dimensional feature space for salinization monitoring,while the research on intensive and long-term salinization monitoring based on three-dimensional feature space model has not been reported.Based on Landsat TM/ETM+/OLI images and three-dimensional feature space method,this study introduced six typical salinization surface parameters,including NDVI（Normalized difference vegetation index）,MSAVI（Modified soil adjusted vegetation index）,SI（salinity index）,Albedo（surface albedo）,I_Fe2O3（Ferric oxide index）,WI（wetness index）to construct eight different feature space monitoring index.Based on the field measured data,the accuracy analysis and comparison were carried out,and the optimal soil salinization monitoring index model of the YRD was obtained.Then,the evolution process and law of salinization in the YRD during 1984-2022 were analyzed and revealed.The response mechanism of salinization evolution to climate-human interaction was discussed by introducing trend analysis method and geographic detector.The main contents and conclusions are as follows:（1）The salinization remote sensing monitoring index method based on three-dimensional feature space model had good applicability for salinization monitoring in the YRD.The salinization monitoring index model of MSAVI-Albedo-I_Fe2O3 feature space based on point-to-point mode had the highest accuracy,with R²=0.93 and RMSE=0.678 g/kg.Followed by NDVI-WI-I_Fe2O3,with R²=0.83 and RMSE=0.799 g/kg.（2）From 1984 to 2022,the mean value of remote sensing monitoring index of salinization in the YRD was 0.97,which belonged to mild to moderate salinization.In the past 39 years,the salinization of the YRD has shown a trend of overall improvement and local intensification.The spatial distribution of salinization intensity showed an increasing trend from the southwest inland to the northeast coast,and the annual average salinization center of gravity continued to migrate to the northeast.The rate of salinization in the northeastern region was greater than that in other regions,and the salinization improvement area was mainly distributed in the cultivated land in the southwest.（3）The high frequency area of non-salinization in the YRD was distributed in the central and southwestern inland areas,while the high frequency area of salinization was mainly distributed in the northeastern coastal areas.The high frequency areas of desalinization,salinization and new salinization were mainly distributed in the main stream and tributaries of the Yellow River.（4）The effects of natural and human activity factors on the salinization process mutually enhanced.There were some differences in the dominant factors in the evolution of salinization in the YRD in different historical periods.The area of salinization evolution affected by climate change and human activities was the largest,3712.47km²,accounting for 53.55%.In the climate-human interaction salinization improvement area,the proportion of areas with human activity contribution>40%was higher than 90%.In the area where salinization is aggravated by climate-human interaction,the proportion of areas with human activity contribution>40%is higher than90%.（5）The effects of natural and human activity factors on the salinization process are mutually enhanced.Among them,soil component factors and vegetation cover factors have the strongest explanatory power for the salinization process and are the dominant factors in the evolution of salinization in the modern Yellow River Delta.