The Spatial Distribution Pattern And Storage Of Organic Carbon In China’s Wetlands Facing Carbon Neutrality

As an important part of the terrestrial carbon pool,wetlands play a crucial role in the global carbon cycle.Wetland organic carbon exhibits high spatial heterogeneity due to its susceptibility to climate change and human activities.The impact of carbon emissions and absorption by wetlands on global climate change has become a matter of great concern worldwide.China has a large number of wetlands,containing a large amount of organic carbon.The estimation of wetland organic carbon storage is of great significance in the context of the national carbon neutral strategy.Despite the availability of wetland area information,sample point information,and spatial interpolation methods,there are still large uncertainties in the organic carbon storage of wetlands in China.Therefore,accurate estimation of organic carbon storage in wetland of China,and understanding of the spatial pattern and storage changes of wetland organic carbon can provide a basis for the protection and scientific restoration of wetlands,thus providing theoretical guidance for the sustainable management of wetlands,which is of great significance to the implementation of carbon neutral strategy in China.Additionally,it can also provide adaptive decision-making advice for wetlands in response to future climate.In this study,a sample database for soil organic carbon and vegetation biomass of wetland was constructed through Meta analysis and field sampling methods.The correlation between soil organic carbon density and vegetation biomass density of wetland and various environmental factors was then analyzed.By leveraging geospatial data of various environmental factors,different machine learning models were established.Using the optimal model,we successfully completed the spatial simulation of soil organic carbon density and vegetation biomass in wetlands.The spatial distribution characteristics of soil organic carbon and vegetation biomass in wetlands were analyzed to assess the differences in various geographical regions and watersheds,as well as the potential impact of future climate change on wetland organic carbon.In view of the current main contradictions and problems faced by China’s wetland protection,targeted suggestions and measures are proposed.This study aims to provide a decision-making basis for coping with global climate change,and provide a strong data support for China to implement the carbon neutral strategy.The main research conclusions are as follows:（1）Based on Meta-analysis and field sampling data,the random forest model performed best to predict and estimate the density and storage of soil organic carbon in wetlands with R² of 0.65.It was found that the spatial distribution of soil organic carbon was significantly affected by various environmental factors,such as temperature,soil,and vegetation.Based on the model prediction,the average soil organic carbon density of wetlands in China is 26.57 kg C m^-2.The density of soil organic carbon shows the trend of higher in the north and lower in the south,and exhibited relatively higher values in the Khingan Mountains and Ruoergai regions.The total storage of soil organic carbon in wetland of China is 4.35 Pg C,in which Northeast China is the concentrated distribution region and accounted for 57.66%of the total soil organic carbon storage.（2）The spatial distribution of vegetation biomass in wetlands is significantly related to elevation and temperature.Higher altitudes generally resulted in lower temperatures,and consequently lower vegetation biomass.Among the different vegetation biomass prediction models,the random forest model has the highest accuracy（R²=0.72）.The prediction results based on this model indicate that the average vegetation biomass density in wetlands of China in 2020 is 240.2 g C m^-2,with higher density in the south,east and coastal areas,and lower density in the west.The total biomass of wetland vegetation in China is 39.23 Tg C,with significant spatial variations.（3）Analysis was conducted on the status,changes and trends of organic carbon storage in wetlands.Results showed that the average organic carbon density in wetlands in China in 2020 is 26.81 kg C m^-2,and the organic carbon storage is 4.39Pg C,inwhich soil organic carbon accounts for 99.08%.In the past two decades,the density of wetland organic carbon increased by 6.09%,but the organic carbon storage of wetland decreased by 8.06%with the decrease of wetland area.Future climate change is projected to have a significant impact on the organic carbon storage of wetlands,with temperature increase of 1.5℃leading to a reduction of 30.48 Tg C in wetland organic carbon storage.Under the low-emission climate model,there is no significant change in the wetland organic carbon storage,while under the high-carbon emission model,the wetland organic carbon storage will decrease by 48.84 Tg C and250.98 Tg C by 2060 and 2100,respectively.（4）At present,the main contradictions and problems in the process of increasing carbon sink,improving carbon storage and realizing carbon neutral strategy in China’s wetlands mainly involve wetland and agricultural development,wetland development and protection,invasive alien species and global climate change.In order to better improve the function of wetlands to increase carbon sink and sequester carbon and implement carbon neutral strategy,we should strictly implement the national spatial planning,classify wetlands for protection and restoration,and establish a long-term protection mechanism for wetlands.