Estimation Of Soil Organic Carbon Storage In Marshes In The Western Songnen Plain

Wetland has praised as the kidney of the earth,with the strongest terrestrial ecosystem service capacity,especially the richest biodiversity and the greatest carbon sequestration potential,which needs the strict protection.Marsh is a typical wetland,which is essential component of the global ecosystem.Carbon accumulation and emission of marshes have played key roles in global climate changes,and have become one of the most concerned issues for governments around the world.The western Songnen Plain is an important distribution area of marshes in China.Accurate estimation of the soil organic carbon storage of marshes in the western Songnen Plain can provide a scientific basis for the wetland protection,utilization and ecological restoration,as well as the theoretical guidance for marsh management.To effectively strengthen the protection of marshes and provide a scientific guidance for the study on the marsh carbon cycle,it is of great significance on carbon storage estimation and carbon cycle researchBased on Landsat 8 OLI remote sensing images,this paper adopted an object-oriented and decision tree classification approach to extract and map marshes in the western Songnen Plain.The classification accuracy was assessed based on field verification points.Marsh soil organic carbon density at each soil sampling point was calculated through field-measured data of the soil profile.The correlation between soil organic carbon density and environmental variables was quantified and analyzed.The environmental variables included topographic indicators(elevation,slope,humidity,etc.),climatic factors(temperature,precipitation,humidity,etc.),remote sensing indices(band reflectance,vegetation reflectance),and other auxiliary variables.Based on the environmental variables,a random forest model was built to achieve the spatial prediction of soil organic carbon density in marshes.Furthermore,the total soil organic carbon storage in marshes of the western Songnen Plain was estimated.The spatial variations of marsh soil organic carbon density was illustrated.The major conclusions of this study are as follows:1.The overall accuracy of marsh classification in the western Songnen Plain was 90%,which met the needs of this study.The total area of marshes is 9656 km2,accounting for 9.51%of the area of whole western Songnen Plain.The spatial variations of marsh distribution was observed,and the majority were distributed in the northern part of the study area,which was consistent with the water resources distribution.2.The soil organic carbon density of marshes in the western Songnen Plain was estimated at depths of 0-30,30-60,and 60-100 cm with values of 6.17 kg/m2,3.02 kg/m2,and 2.79 kg/m2,respectively.The soil organic carbon density of 0-30 cm was 50.34%of that of the total soil profile.Soil organic carbon density decreased with increasing depths.3.Different environmental variables have various effects on soil organic carbon density of marshes in the western Songnen Plain.Climatic factors were strongly related to soil organic carbon density.Indeed,soil organic carbon density has a significantly negative relationship with annual average temperature and the annual average precipitation,while a significantly positive correlation between annual average humidity and soil organic carbon density was shown.The correlations of soil organic carbon density with remote sensing indices were significant.Specifically,the correlation of soil organic carbon density with net primary productivity was positive,while that of soil organic carbon density with land surface water index was negative.The correlations between topographic indicators and organic carbon density were weak.4.Spatial prediction of soil organic carbon density in marhes of the Songnen Plain was achieved with the root mean square error below 5.26 kg/m2 through the random forest model.The topsoil(0-30 cm)organic carbon density was obviously higher than that in the middle(30-60 cm)and bottom(60-100 cm)layers.Spatially,the soil organic carbon density in the north was evidently larger than that in the south.It increased with the growth of the latitude.The soil organic carbon storage of marshes in the western Songnen Plain was estimated as the value of 1.24×108t.