Study On The Optimization Of Soil Erosion Calculation Methods In Black Soil Region Of Northeast China Based On Slope Length Factor

Soil erosion is one of the major global environmental problems.Our country is one of the most eroded countries in the world,and soil erosion in the black soil region of the north-east is also very serious.Soil erosion in the black soil areas of the north-east is increasingly threatening the food security of the country.Accurate soil erosion forecasting is the basis for developing reasonable soil and water conservation measures.Slope length is an important factor affecting soil erosion.The edges of the Northeast Black Soil Area parcels often contain features such as forest belts,drainage ditches and roads.These features can intercept runoff and slope length and reduce the slope length factor of soil erosion.They are collectively referred to in this paper as "parcel border features(PBF)".When the model is used to calculate soil erosion rates,it can overestimate the slope length factor,and therefore the amount of soil erosion,if it does not take into account PBF.However,there is currently a lack of quantitative understanding of this question.For this purpose,three typical sub-watershed in the northeastern black soil area(Weizigou 1,Hebei and Dafangshen)were selected as the study areas,and field survey data and DEM data were used to analyze the effects of PBF on the slope length factor(L)and soil erosion rate(A),and the effects of intervals between cross-slope PBFs on the slope length factor(L).The main results of this study are as follows:(1)The PBF truncated slope length,which makes the topographic slope length(λD)of the watershed different from the erosion slope length(λ).The average λD is 129.75 per cent higher than the average λ in the Weizigou 1 watershed,70.16 per cent higher than the average λ in the Hebei watershed and 34.22 per cent higher than the average λ in the Dafangshen watershed.The smaller the topographic fluctuations in the watershed,the more regular the distribution of PBF,the greater the difference between λD and λ,and the greater the degree of overestimation of slope length.(2)The slope length is truncated by PBF,which in turn affects the slope length factor.The mean λD of Weizigou 1 watershed is 14.19 per cent higher than the mean λ;the mean λ of Hebei watershed is 17.97 per cent higher than the mean λ;and the mean λ of Dafangshen watershed is 13.4 per cent higher than the mean λ.(3)The rate of soil erosion in the watershed is proportional to the topographic fluctuations.At the same time,influenced by the slope length factor,the overestimation of soil erosion rate in the three watersheds,the Hebei watershed was the largest at 94.82%,while the Weizigou 1 watershed and the Dafangshen watershed.were smaller at 36.69% and 18.02%,respectively.(4)The extent to which the slope length factor is overestimated is related to the slope and intervals between cross-slope PBFs.The degree to which the slope length factor is overestimated is positively correlated with the slope length exponent,i.e.,it is positively correlated with the slope.The smaller the intervals between cross-slope PBFs,the greater the impact on the slope length factor.Therefore,all other things being equal,the greater the slope and the smaller the intervals between cross-slope PBFs,the more important it is to calculate soil erosion using erosion slope length indicators that take into account ground cutoffs.(5)The soil erosion rate calculation for the northeast black soil area should take into account the truncation of the slope length by PBF and replace the topographic slope length with erosion slope length to make the soil erosion rate calculation more consistent with the true value.