Remote Sensing Characterization Of Soil Erosion Intensity And Its Impact On The Spatial Pattern Of Cropland Carbon Sequestration Potential In The Degraded Black Soil Region

With the increasing pressure of high-intensity human activities on land resources,land degradation,with soil erosion at its core,has become increasingly prominent,posing a serious threat to global food and ecological security.In the black soil area of Northeast China,the fertile black soil resources formed since the Holocene have been affected by extensive cultivation and rough management,and degradation problems such as thinning of the black soil layer and decreasing of Soil Organic Carbon（SOC）content have occurred.Soil erosion in degraded black soil areas not only causes a decline in soil quality,but the lateral transport of materials driven by soil erosion is also closely linked to the carbon cycle of terrestrial ecosystems and interferes with the source-sink function of the soil carbon pool.Although the academic community has formed a broad consensus on the seriousness of the soil erosion problem in the black soil zone,it is still difficult to synchronize the fine identification of local hotspot areas of soil erosion in the black soil region and the regional comprehensive evaluation due to the limitation of the precision and timeliness of the traditional methods of soil erosion investigation and quantitative evaluation,which further restricts the research of the spatially differentiated constraints on the carbon sequestration potential of arable land due to soil erosion.To this end,this paper takes the thin-layered black soil area in central Jilin Province as the study area,integrates soil parametric remote sensing inversion,soil-landscape model simulation,soil carbon fraction technology and other diversified research methods,applies soil visible-near-infrared spectroscopy technology to spatial simulation of soil erosion,constructs a fine spatial characterization method of the intensity of soil erosion in the black soil area,and realizes the precise identification of the hotspot of soil erosion at the watershed and regional scales.In addition,the spatial evaluation of soil carbon sequestration potential was carried out,revealing the influence mechanism of soil erosion on the spatial variation of carbon sequestration potential of arable land,and laying a theoretical and methodological foundation for the spatial investigation and control of black soil degradation,as well as carbon sequestration and emission reduction of soil.The main research contents and results are as follows:（1）Optical remote sensing identification of soil erosion intensity at watershed scaleAiming at the lack of spatial characterization methods for high-resolution soil erosion intensity in black soil areas,the feasibility of spectral diagnosis of soil erosion intensity was firstly verified.Combined with training data from the ¹³⁷Cs nuclide tracer method,the theoretical and methodological feasibility of soil visible-near-infrared spectral characterization for soil erosion intensity classification was demonstrated at the watershed scale.It was found that different erosion intensities showed significant differences in spectral features in the visible-near-infrared band due to soil erosion-driven topsoil transport and spatial redistribution.Based on the response relationship between soil spectral features and erosion intensity,a spectral classification model of soil erosion was constructed in a sequential manner for both laboratory near-earth sensing and satellite remote sensing platforms,and spatial characterization of soil erosion intensity at the watershed scale was realized,with the areas of severe erosion,moderate erosion and deposition accounting for15.9%,65.4%and 18.7%of the total cropland area,respectively.Compared with the spatial simulation results based on the generalized soil loss equation,the spatial distribution characteristics of the soil erosion classification results based on soil spectral information are similar,but with higher resolution,which is more suitable for the identification of severe erosion hotspots.The spatial superposition comparison with the normalized vegetation index during the growing period of maize revealed that the soil erosion intensity showed a significant negative spatial correlation with the production status of maize,which proved the prediction accuracy of this soil erosion classification method from a spatial perspective.（2）Upscaling studies:remote sensing modeling of soil erosion intensity at the regional scaleOn the basis of the feasibility verification at the watershed scale,an upscaling study was carried out and a large-scale regional soil erosion remote sensing modeling and spatial mapping method was constructed.A“two-step”remote sensing classification and modeling scheme for soil erosion intensity was developed based on the integrated process of bare soil image recognition,multi-temporal composition and soil mapping feature extraction.In the first step,Google Earth’s Very High Resolution（VHR）images were used to extract the“heavily eroded zone”,“sedimentary zone”and“moderately eroded zone”as training sample points,and a random forest classification model was established,with a prediction accuracy of 80%,which was mainly attributed to the significant importance of the red edge band and the slope factor.In the second step,to address the problem of high proportion of moderate erosion zone（>58%）,the Iterative Self Organizing（ISO）unsupervised classification method was used to further subdivide the moderate erosion zone,and a five-level classification map of soil erosion intensity at 10 m resolution was generated for the study area.The validation of the accuracy of the classification results showed that,at the watershed scale,there were significant differences in the soil loss rates corresponding to different erosion intensity classes,with the soil loss rate in the severely eroded area reaching5.5 mm/yr.At the regional scale,by comparing the SOC contents corresponding to different erosion intensity classes,it was found that the SOC contents showed a decreasing trend from the depositional area to the severely eroded area.From the spatial perspective,there was also a negative correlation between soil erosion intensity and crop growth at the regional scale,and this negative correlation was more significant in the selected local areas.The above results show that the classification and spatial characterization of soil erosion intensity based on Sentinel-2 bare soil mapping features has the advantages of high precision,high resolution and high timeliness,and has a broad application potential in the field of land degradation investigation and monitoring in the black soil area.（3）Spatial evaluation of soil carbon sequestration potential of arable land based on soil carbon saturation theoryA quantitative estimation and spatial mapping method of soil carbon sequestration potential in arable land based on soil-landscape model was established.The concept of soil carbon saturation and soil carbon fraction technology were introduced,and the quantitative estimation of soil carbon sequestration thresholds and sequestration potentials based on the core coefficients of clay,silt and mineral-associated organic carbon（MAOC）was realized by combining the Fourier infrared transform（FTIR）spectroscopic data and memory learning modeling,in which the MAOC prediction accuracy（expressed by the coefficient of determination R²）reached 0.98 based on FTIR data.The accuracy of MAOC prediction based on Fourier transform spectral data（expressed as the coefficient of determination R²）reached 0.98.Based on the point data of soil carbon sequestration potential,the spatial mapping of soil carbon sequestration potential from point to polygon was further realized.Climate,terrain,soil,vegetation and spectral index were selected as covariates,and a random forest prediction model for the carbon sequestration potential of arable land in the black soil zone was established based on the theory of the SCORPAN soil-landscape model,with a prediction accuracy of R² of 0.65 and a root-mean-square error of 1.42 kg/m².In terms of spatial differentiation,the carbon sequestration potential of cropland showed an increasing trend from west to east,with the southwestern and west-central regions showing lower sequestration potentials of less than 10 kg/m²,while the southeastern region presented the greatest soil carbon sequestration potentials,averaging more than 15 kg/m².（4）Mechanisms constraining the spatial differentiation of carbon sequestration potential of cropland by soil erosion patternsSynthesizing the results of spatial characterization of soil erosion intensity and soil carbon sequestration potential of cropland,a study on the mechanism of the influence of soil erosion pattern on the spatial differentiation of carbon sequestration potential of cropland was carried out.The constraints of soil erosion intensity on the carbon sequestration potential of cropland were analyzed at the regional and field scales using Random Forest Variable Importance Analysis,Partial Dependence（PD）analysis,Shapley Additive Explanations（SHAP）analysis,and Geo Detector.The results showed that soil erosion intensity was a significant role factor in the spatial evaluation model of cropland carbon sequestration potential.With the increase of soil erosion intensity,the carbon sequestration potential of cropland generally showed an increasing trend,but this positive relationship differed in strength depending on soil type and spatial scale.In addition,the carbon sequestration potential of cropland was also influenced by environmental covariates such as multi-year annual precipitation and temperature,spectral index,and to a lesser extent by topographic factors.However,the same variable was affected by the intensity of soil erosion in different roles in localized areas.The interaction detection analysis revealed that the interaction of any two of the above factors positively contributed to the soil carbon sequestration potential.In summary,this paper realizes the spatial identification of soil erosion hotspots by establishing the remote sensing evaluation method of soil erosion intensity and soil carbon sequestration potential,reveals the mechanism of soil erosion in the black soil region on the soil carbon pool and carbon sequestration potential of agricultural land,and provides a new methodology and a new way of thinking for spatial investigation and evaluation of land degradation in the black soil region,and provides scientific bases for the formulation of land degradation control and prevention measures,the promotion of soil carbon sequestration and reduction of emissions,and the improvement of the function of soil carbon sinks.It provides scientific basis for the formulation of land degradation control measures,promotion of soil carbon sequestration and emission reduction,and improvement of soil carbon sink function.