Impacts Of Surface And Gully Erosions On Soil Aggregate And Organic Carbon Losses In The Typical Black Soil Region

Soil aggregate and soil organic matter losses are the major forms of soil degradationprocess in the typical black soil region. In order to analysis the influence of soil aggregate andorganic carbon loss at surface and gully erosion processes at sloping farmland in northeastblack soil area, this thesis designed different rainfall simulation experiments, includingdifferent intensities of rainfall and inflow, and combination of rainfall and inflow, to researchthe differences of surface and gully erosions and to analyze the relationship between soilaggregate loss and soil organic carbon loss. The main results obtained are as follows:1. Studied the differences of the surface and gully erosion at sloping farmland. Under therainfall intensities of50and100mm/h, the sediment amount in the gully erosion was almost1.42and3.51times greater than that of surface erosion, respectively. Under differentconbination of rainfall and water inflow, including (50+50),(100+100),(50+100) and(100+50) mm/h, the soil loss at the treatment of gully erosion were about2.38,1.23,8.38and3.04times to the treatment of surface erosion, respectively. Under the same condition of theinflow intensity, when the rainfall intensity increased from50to100mm/h, the amount ofsoil loss increased by89.6-97.3%at the treatment of surface erosion, as well as the treatmentof gully erosion, which increased by81.8-99.7%. While under the same condition of therainfall intensity, when the inflow intensity increased from50to100mm/h, the amount ofsoil loss increased by17.2-78.4%at the treatment of surface erosion, as well as the treatmentof gully erosion, which increased by45.4-76.5%. As a result, at these two treatments ofsurface and gully erosions, increased rainfall intensity to the soil loss amount was greater thanthat of increased intensity of inflow.2. Investigated how surface and gully erosion affected the soil aggregates losses. Whenrainfall intensity increased from50to100mm/h,<0.25mm of micro-aggregates inthe sediment from surface erosion treatment increased from45to74%; while for gullyerosion treatment, aggregate in sediment was mainly≥0.25mm of macro-aggregates, whichoccupied65.5%of total aggregates loss. Compared with the test soil, mean weight diameter(MWD) and geometric mean diameter (GMD) of aggregates in the sediment for bothtreatments of surface and gully erosion were decreased. Under two rainfall intensities of50 and100mm/h, MWD and GMD in sediment from the surface erosion treatment were lessthan those from the gully erosion treatment. This paper also proposed that under theexperimental condition, two indicators of MWD and GMD could reflect the lost aggregatecharacteristics, and MWD could be better to reflect aggregate variation with an increase ofrainfall intensities. Under the relatively smaller rainfall and inflow intensities condition, theratio of lost macro-aggregate and micro-aggregate ratio was averaged from the two treamentsof surface and gully eroison. While under the relatively larger rainfall and inflow intensitiescondition, aggregate in sediment was mainly macro-aggregates, which occupied68%of totalaggregates loss. In these two conditions, the indicators of MWD and GMD could well reflectthe changed intensity of rainfall and inflow, however, they cound not tell the two erosiondifferences and lost aggregate characteristics. In the larger inflow intensity combination trial,aggregate in sediment was mainly micro-aggregates, which occupied73%of total aggregatesloss at the surface erosion, while the macro-aggregates occupied61%were mainly lost objectat the gully erosion. In larger rainfall intensity combination, the ratio of lost macro-aggregateand micro-aggregate ratio was averaged at surface eroison, but at the gully erosion, aggregatein sediment was mainly micro-aggregates, which still occupied61%of total aggregates loss.The indicators of MWD and GMD could well reflect the two erosion differences and lostaggregate characteristics under these two conditions.3. Studied the results of soil organic carbon (SOC) loss in different erosion processes, aswell as the SOC distribution in different graded aggregate. Under the rainfall intensities of50and100mm/h, the SOC loss in the gully erosion was almost1.65and3.74times greater thanthat of surface erosion, respectively. Under different conbination of rainfall and inflow,including (50+50),(100+100),(50+100) and (100+50) mm/h, the SOC loss at the treatment ofgully erosion were about2.39,1.26,6.20and2.54times to the treatment of surface erosion,respectively. The content order of SOC in different graded aggregates in the sediment was:0.25-0.5、0.5-1、1-2、2-5、≥5、<0.25mm. Among these six different graded aggregates in theerosion sediment, there was a linear relationship between the soil aggregate loss and SOC loss,compared the SOC content of aggregates in the test soil, there was less difference in SOCcontent of aggregates in the sediment.