Study On The Contribution Rate Of Soil Surface-subsurface Loss And Its Influencing Factors In A Typical Areas Of Karst Rocky Desertification In Plateau Mountains

Soil erosion has always been the center of attention and study in the field of rocky desertification control because it is the primary factor in the development and evolution of rocky desertification.The unique binary structure in karst areas results in dual characteristics of soil and water loss,including surface erosion and underground leakage.However,there is still limited research on the contribution rate and occurrence mechanism of underground leakage in this area.Therefore,exploring the characteristics and influencing factors of soil surface/underground loss in karst rocky desertification areas is of great significance.This study focuses on the demonstration area of potential to mild rocky desertification comprehensive management in the mountainous areas of the Salaxi Plateau in Bijie,Guizhou,which is highly representative of both the process of rocky desertification and the comprehensive management of rocky desertification.Eight runoff plots under two different levels of rocky desertification and four typical land use types are selected as the research objects.Based on the precipitation characteristics and soil physical and chemical indicators of the study area,a research method combining surface erosion and underground leakage is adopted,Analyzed the characteristics of soil surface erosion and underground leakage changes in runoff plots,explored the proportion characteristics of soil surface erosion and underground leakage in karst areas,and analyzed the impact of different land use methods on karst binary structure soil erosion based on factors such as rainfall,basic soil physicochemical properties,aggregate characteristics,and soil nutrients.The main conclusions are as follows:(1)Soil underground leakage accounts for absolute advantage in the total annual erosion.From May 2021 to May 2022,the average total loss of 8 runoff communities was 26.87 kg,mainly concentrated from May to September,accounting for 67.88% of the total annual loss.The highest value occurred from May to June,accounting for 24.02% of the total annual loss.The lowest value occurred from November to March of the following year,only accounting for 4.04% of the total annual loss;The average amount of surface erosion was 4.76 kg,showing a pattern of mild rocky desertification(5.16 kg)>potential rocky desertification(4.37 kg).From a time cycle perspective,the amount of soil surface erosion roughly shows a trend of first increasing and then decreasing,concentrated in May to September,and the erosion amount in these five months accounts for 91.46%of the total annual erosion amount;The average underground leakage amount is 22.10 kg,and the variation pattern is similar to the total loss amount.The amount of soil underground leakage in each runoff plot accounts for 73.29%～89.52% of the total amount of soil erosion,with an average proportion of 83.58%,which indicates that in this experiment,soil underground leakage is the main loss.(2)Rainfall,intensity of rocky desertification,and land use patterns have significant impacts on surface underground soil erosion.During the monitoring period,the total rainfall in the research area was 1278 mm,mainly concentrated from May to September.The soil erosion amount in the rainy season accounted for 67.88% of the total soil loss amount throughout the year,and the average soil loss amount in the dry season was32.12%.In particular,the surface soil loss was highly concentrated in the rainy season,accounting for 91.46% of the total surface soil loss amount on average,and only 8.54% in the dry season;Under the same land use pattern,whether it is surface erosion or underground leakage,the soil erosion modulus of potential rocky desertification is lower than that of mild rocky desertification.The contribution rate of surface erosion in runoff plots of mild rocky desertification is greater than that of potential rocky desertification,while the contribution rate of underground leakage is the opposite,reflecting that the degree of rocky desertification is an important factor affecting soil erosion in karst areas.Mixed vegetation types are more conducive to the prevention and control of soil erosion.Compared to single land use types,the total soil erosion modulus of forest shrub grassland can be reduced by 44.10% at most and 19.09% at least.The surface erosion modulus of cultivated land is higher than that of forest shrub grassland by more than 75%,68%,and 44%,respectively.From the perspective of underground leakage,the difference in the soil erosion modulus caused by land use methods is significantly small,ranging from 5% to 33.97%.(3)Varied soil physical and chemical features have varied effects on the surface and subterranean soil erosion characteristics.The changes in soil bulk density,porosity,and moisture content between different runoff plots are modest,and the link with runoff plot loss characteristics is weak.Soil stability MWD and GMD values are lowest in cropland,potential stone desertification plots are higher than light stone desertification runoff plots,and erodibility is highest in cropland.There were highly significant negative correlations between total loss,surface loss,subsurface loss and large aggregates(>2 mm),MWD and GMD;conversely,there was a highly significant positive relationship with soil aggregates of 0.053-0.25 mm grain size and erodibility K values.Forests and irrigated grasslands have the highest levels of soil total nitrogen,total phosphorus,and organic carbon,and there is a general trend that potential stone desertification plots have higher organic carbon content than light stone desertification plots.Total loss,surface loss,soil organic carbon,and total phosphorus concentration all had highly significant relationships.Redundancy analysis(RDA)results revealed that soil aggregate particle size distribution,stability features,soil erodibility K values,soil organic carbon,and total phosphorus content were key factors in the explanation of the soil erosion process in runoff plots.The study’s conclusions provide a theoretical framework for comprehending how rocky desertification developed and for examining comprehensive soil and water conservation methods.