Study On The Temporal And Spatial Characteristics Of Water Erosion And Sediment Production Or Transport In Watershed Of The Black Soil Region,Northeastern China

Black soil is known as"the giant panda in cultivated land".The black soil region in Northeast China is severely suffering freezing and thawing activity and snowmelt runoff erosion,and its erosion amount accounts for a large proportion of the whole year.In the present study,fifteen watersheds in the black soil region were selected as the research object,and the spatiotemporal distribution characteristics of water erosion in the watershed and their influencing factors were explored and analyzed using statistical analyses and water erosion models,in combined with runoff and sediment monitored data from hydrological stations and field observation.The potential influencing factors of soil erosion and sediment yield,including freezing and thawing factors,watershed morphology,meteorology and hydrology,and underlying surface properties were used to explain the variations of soil erosion and sediment yield of the watersheds.The contributions of snowmelt runoff erosion to the annual total were also given by using correlation analysis and multiple linear regression methods.The specific conclusions are as follows:（1）The duration of freezing and thawing activity was becoming shorter for the eastern watersheds,and longer for the western watersheds in the study region.Due to global warming,the freezing and thawing duration in the study area is decreasing at a rate of 3.9 d·10a^-1,with an average of 201.6 days.the spatial distribution characteristics were strongly influenced by latitude,terrain,and altitude.In recent years,the freezing index has significantly decreased and the melting index has significantly increased.The air freeze thaw index ranged from 1280.8 to3350.1℃·d and 1865.8 to 3629.0℃·d,respectively,while the ground freeze thaw index ranged from 830.4 to 2881.7℃·d and 2478.5 to 4302.7℃·d,and the change rates from 2000to 2020 were-5.26,6.01,-13.58,and 9.84℃·d·a^-1,respectively.（2）The rainfall erosion and snowmelt erosion modulus of the watersheds were larger in the southeast.The rainfall and snowmelt erosion modulus in No.10 watershed which controlled by Min Li station were the largest,with values of 5556 t/km²·a and164 t/km²·a.The interannual variation of rainfall erosion modulus in No.3 which controlled by Liang Jiazi station watershed was the largest,with a coefficient of variation of 93.42%.For the study watershed,most of them were suffering mild erosion,and there has been no transition in the erosion level during the study period.No.10 watershed has suffered an extremely severe erosion stage from a mild erosion stage,with a coefficient of variation of 52.45%.Although it had decreased in2020,it was still in a severe erosion stage.（3）The annual watershed sediment t modulus ranged from 3.42 to 390.81 t/km²·a,and those derived from snowmelt runoff ranged from 1.30 to 21.29 t/km²·a.The snowmelt and yearly soil erosion modulus of No.10 and No.7 controlled by Wu Daogou station watersheds were both the two largest ones the 15 watersheds.During the study period,the average snowmelt erosion modulus reached 21.29 t/km²·a and 20.44 t/km²·a,respectively,while the annual erosion modulus reached 390.81 t/km²·a and 111.42 t/km²·a.From the perspective of spatial distribution characteristics of watersheds,there is a significant difference among watersheds,and the spatial distribution regularity of snowmelt and annual erosion modulus were poor.It may be related to the complex and variable meteorological and hydrological factors and underlying surface factors of the watersheds.（4）During the study period,the annual watershed sediment modulus（SSY）was negatively correlated with watershed perimeter（Pe）and forest area ratio（PF）at the level of0.05,with correlation coefficients of-0.54 and-0.70,respectively,and also negatively correlated with vegetation coverage（PV）,with a correlation coefficient of-0.30.Forest land has a significant inhibitory effect on soil erosion and sediment yield.The key driving factors affecting erosion and sediment yield（SSY＿s）during snowmelt period in a watershed were snowmelt runoff depth（Hs）,temperature freezing index（TEM＿FI）,temperature melting index（TEM＿TI）,low temperature freezing index（GST＿FI）,ground temperature melting index（GST＿TI）,and forest land percentage（PF）,which were significantly correlated at the level of0.05.The absolute value of the correlation coefficient was greater than 0.51,and the correlation coefficient between the proportion of forest land and the sediment transport modulus during the snowmelt period was the largest,with a correlation coefficient of 0.73.（5）The key driving factors affecting the contribution of snowmelt erosion to annual total C_SY in the 15 watersheds are watershed area（A）,forest land percentage（PF）,freeze thaw duration（FT）,soil erodibility factor（Ks）,annual snowfall（Fs）,annual snowfall to precipitation ratio（Ps）,and annual runoff depth ratio（Pr）during snowmelt.The partial least squares regression model expression was C_SY=0.439+0.556+0.639+0.161-0.106+0.771+0.562-0.256,with a model determination coefficient of R²=0.798.