Evolvement Of Soil Erosion And Sediment Transport In Typical Black Soil Small Watershed

Due to its special features of topography and soil properties, the soil and waterloss in the Black soil area of Northeast China is significant difference from that in theLoss Plateau of Northwest China. Soil and water loss was/is the main reason of blacksoil degradation. The deterioration of soil physical and chemical characters andfertilization have greatly threatened soil productivity and food security of China. Thelarge scale Balck soil erosion in Northeast China has been progressed. However, fewstudys focused on slope soil and gully erosion and their influencing factors in smallwatershed. This study was carried out in a small watershed scale in typical black soilarea of Northeast China. The surface soil erosion was evaluated by USLE model, andgully erosion was evolutated by remote sensing data, topography data as well as field-survy during the past41years. The primary results were as follows:The study area was/is being under intensive surface erosion, and the predictedaverage annual soil loss was3454.7t/(km~2·a). More than95percent of eroded soilwas deposited in the watershed; very little sediment reached the river in the form ofsediment yield.32.7percent of total small watershed area where was in severelyintense erosion, which created79percent of total small watershed sediment; there was37.6percent of small watershed area was slightly eroded, but only5percent of totalsmall watershed sediment was yielded.There was a significant relationship between predicted soil loss amount and landuse. All of the predicted soil loss amount of very severe and extreme soil erosion waslocated in conventional tillage area; and also half area of the predicted severe soilerosion located in conventional tillage;80percent of moderate soil erosion was found in shrubbery buffer strip with bund area; all of slight soil erosion located in soil andwater conservation tillage area; the prediction showed the soil loss intensity wasmoderate in forest area.The trend of gully erosion in study area was/is becoming severely during the past41years. The gully erosion indensity increased from3.33km/km~2in the year of1968to4.96km/km~2in2009, namely increased from very severe to extreme. The gullyeroded area increased from0.86km~2to2.22km~2, and its percentage increased from3.6percent to9.2percent in the same period. The units of farmland were increasedfrom27to68due to gully erosion.The process of slope erosion was affected by soil and water conservationmeasures, slope steepness along the ridge direction and slope length; Slope steepnessis one of natural factors, which determines the location gully formed and gully size;agriclutral practice management is one of artifical factors, which determines the speedof the gully develepoment and its intension.In order to efficiently protect the eroded farmland, the soil and waterconservation measures should preferentially applied in high slope steepness area,namely in the extreme soil erosion area,32.7percent of total watershed area,80percent sidements was formed; The prediction result showed the soil erosion intensionin the total small watershed would decrease to slight under soil and waterconservation measures.