Effects of soil rock fragment content on the USLE-K factor estimating and its influencing factors

Rock fragments are an important component of soil,and their presence has a significant impact on soil erosion and sediment yield.In this paper,the effects of rock fragments in the topsoil profile(RFP)and rock fragments on the soil surface(RFS)on the soil erodibility factor(K)were assessed at a global scale.The spatial pattern of the relationship between stoniness and erodibility(RS-K)and its predominant factors were explored through correlation analysis,pattern analysis,and random forest model analysis.The results were as followings:(1)The existence of RFP increased K by 2.84%.The RFS of the mountain land and desert/Gobi reduced K by 18.7%;therefore,once the RFP and RFS were taken into account in the calculation,K was 6.98%lower.(2)The predominant factors of the effect of RFS and the joint effect of RFP and RFS were elevation and slope gradient.The predominant factors of the effect of RFP were annual average precipitation and annual average temperature.(3)In assessing and mapping soil erosion in large regions,special attention should be given to areas with large rock fragment contents,a relatively high altitude,and the presence of steep slope.If rock fragments were not taken into consideration,the mapping results of soil erosion may be biased.This article made the calculation of K more complete and accurate,thereby improving the accuracy of regional soil erosion estimation.This research was of sig-nificance for the investigation of global hydrological effects and simulation of the global soil carbon budget.

Impacts of horizontal resolution and downscaling on the USLE LS factor for different terrains

Slope length and slope steepness are critical topographic factors(L and S)in the Universal Soil Loss Equation(USLE)and Chinese Soil Loss Equation(CSLE)for soil erosion modelling.Both slope length and slope gradient are potentially sensitive to spatial resolution when calculated in a GIS framework.The resolution effect on the LS factor and approaches suitable for improving the LS factor at a coarse resolution have not been well identified.To address this problem,the LS factor at 5-m and 30-m resolution in twenty-four watersheds with various terrains was estimated.And a downscale model based on matching of the lower resolution LS cumulative frequency curves to a higher resolution("Histogram Matching"method)was tested for its potential to improve LS factor estimation accuracy.In the larger relief mountainous area,compared to 5-m resolution,the 30-m resolution generated LS was generally overestimated by more than 20%and in lower relief areas underestimated by more than 15%.This bias is less than 10%in medium relief areas.The downscale model improved LS factor estimates compared to the 30-m resolution estimate by more than 10%when comparing frequency distribution curves and more than 20%in mean values in larger relief areas.The downscale model worked well in all regions except for the low relief areas,which intuitively are the low soil erosion potential areas.The results of this research help quantify the uncertainty in soil erosion estimates and may ultimately help to improve the assessment of soil erosion through its impact on LS factor estimates,especially at regional and global scales.

Study on a soil erosion sampling survey in the Pan-Third Pole region based on higher-resolution images

Soil erosion is one of the most severe global environmental problems,and soil erosion surveys are the scientific basis for planning soil conservation and ecological development.To improve soil erosion sampling survey methods and accurately and rapidly estimate the actual rates of soil erosion,a Pan-Third Pole region was taken as an example to study a methodology of soil erosion sampling survey based on high-spatial-resolution remote sensing images.The sampling units were designed using a stratified variable probability systematic sampling method.The spatiotemporal characteristics of soil erosion and conservation were taken into account,and finer-resolution freely available and accessible images in Google Earth were used.Through the visual interpretation of the free high-resolution remote sensing images,detailed information on land use and soil conservation measures was obtained.Then,combined with the regional soil erosion factor data products,such as rainfall-runoff erosivity factor(R),soil erodibility factor(K),and slope length and steepness factor(LS),the soil loss rates of some sampling units were calculated.The results show that,based on these high-resolution remote sensing images,the land use and soil conservation measures of the sampling units can be quickly and accurately extracted.The interpretation accuracy in 4 typical cross sections was more than 80%,and sampling accuracy,described by histogram similarity in 11 large sampling sites,show that the landuse of sampling uints can represent the structural characteristics of regional land use.Based on the interpretation of data from the sample survey and the regional soil erosion factor data products,the calculation of the soil erosion rate can be completed quickly.The calculation results can reflect the actual conditions of soil erosion better than the potential soil erosion rates calculated by using the coarse-resolution remote sensing method.

Quantitative assessment of the influence of terrace and check dam construction on watershed topography

Terrace and check dam construction has substantially changed land surface morphology,which in turn affects modern surface processes.Digital elevation models(DEMs)provide an effective way to quantitatively analyze surface morphology and processes.However,existing DEMs lack sufficient ability to express artificial terrain.Based on 1:10000 topographic maps of the Zhifanggou watershed,a series of artificial terrain DEMs for the study site were constructed by both field investigation and remote sensing images from 1938 to 2010.Digital terrain analysis was used to quantitatively assess the influence of terrace and check dam construction on the watershed terrain.The results showed that the artificial terrain DEM could capture the spatial distribution patterns of terraces and dam lands and improved the ability of DEM to express terrain.The construction of terraces and check dams clearly changed the surface elevation.The average elevation change of each terrace mainly ranged between–1.5 and 1.5 m,while the annual average deposition height of the dam lands was 9.16 cm.The average slope,slope length,and slope length and steepness factor of the watershed decreased with the effect of the artificial terrain on the surface,and their averages decreased by 0.65°,6.75 m,and 0.83,respectively,from 1938 to 2010.Although the construction of terraces reduced their surface slope to nearly 0°,the slope of terrace embankments rapidly increased,to more than 45°,which may lead to gravitational erosion and potential terrace damage.Terracing reduced the slope length in both the terrace distribution area and downslope of the terraces.Check dam deposition reduced the slope and slope length of the channel.This study contributes to a better understanding of the topographic change rules after terrace and check dam construction,and aids in elucidating the mechanisms of soil erosion process influenced by artificial topography.

Unpaved road erosion after heavy storms in mountain areas of northern China

More frequent extreme rainfall events associated with global climate change cause greater challenges for soil conservation.Severe erosion occurs on many unpaved roads since these structures create important water flow paths during heavy storms.The present research aimed to investigate the intensity and influencing factors of unpaved road erosion under varied land use and management conditions(sloping cropland,terraced cropland,forest&grass).The erosion occurred in the watersheds contributing runoff water to roads after the greatest rainfall event recorded in the mountain area of northern China caused by Typhon Lekima.The research was conducted in an agricultural-forest-dominated watershed based on field investigation and UAV-based image analysis.A road erosion level classification standard was given according to the occurrence of rills,ephemeral gullies,and gullies.Significant erosion happened on 67% of the unpaved roads;42% of them suffered moderate to severe erosion in which ephemeral gullies or gullies developed.The average erosion amount from these roads was 2280.75 t ha-1 and was significantly influenced by the watershed land use type and management.The dominant factor governing unpaved road erosion associated with terraced cropland was vegetation coverage on roads.Drainage area was the most important factor for road erosion in sloping cropland and forest&grass land,and road gradient was also a critical factor.Terraces,and forest&grass in drainage areas significantly reduced unpaved road erosion by 85%and,47%,respectively,compared to sloping cropland.More integrated measures should be used to prevent unpaved road erosion.The results of this research can be applied to road protection against erosion in heavy storms.