Impacts Of Soil Erosion On Soil Aggregates And Particles Losses In The Black Soil Region

Black soil region of Northeast China was one of regions which faced serious soil erosion.Soil aggregates and particles losses were caused by soil loss, which directly threatend theproduction and development of agriculture in black soil region. This thesis, based on rainfallsimulation and confluence scour experiments and laboratory analysis, studied the differencebetween surface and gully erosions, and analyzed the influence of soil aggregates andparticles losses at surface and gully erosion processes. The main conclusions are as follows:(1) The differences of the surface and gully erosion chractresitics were analyzed. Runoffand soil loss increased with the increase of rainfall and confluence intensity. Runoff and soilloss of gully erosion were much greater than surface erosion, which were1.1times and2.8times than these of surface erosion, respectively. The increase of runoff and soil loss with theincrease of rainfall intensity was significantly greater than those with the increase ofconfluence intensity. Under surface erosion, increased runoff rate and increased soil loss ratewere48.1%-61.0%and82.5%-91.3%resulted from increasing the50mm/h rainfall intensity.Likewise, increased runoff rate and increased soil loss rate were19.4%-37.1%and9.5%-71.6%resulted from increasing the50mm/h confluence intensity. Under gully erosion,increased runoff rate and increased soil loss rate were55.2%-59.6%and68.3%-88.9%resultedfrom increasing the50mm/h rainfall intensity. Likewise, increased runoff rate and increasedsoil loss rate were33.3%-45.5%and19.5%-80.0%resulted from increasing the50mm/hconfluence intensity.(2) Effects of surface and gully erosions on soil aggregates losses were studied.Comparing with the test soil, the proportion of macroaggregates in the sediment reduced by3%-52%, while microaggregates increased by1%-62%. The dominated aggregate loss size inthe sediment was＜0.25mm, which occupied46.5%of the total aggregates loss.0.25-0.5mm increased resulted from>1mm aggregates in sediment broken. Comparing with the testsoil,>1mm aggregates in the sediment decreased by38%, while0.25-0.5mm aggregateswere2.3times than that of the test soil. Comparing with the test soil, mean weight diameter(MWD) and geometric mean diameter (GMD) of aggregates in the sediment decreased. MWDand GMD of surface erosion were generally less than gully erosion. MWD and GMD of surface erosion decreased with the increase of rainfall and confluence intensity; MWD andGMD of gully erosion increased as rainfall intensity increased. MWD and GMD could wellreflect aggregates losses.(3) Effects of surface and gully erosions on soil microaggregates losses were analyzed.Comparing with the test soil,0.087-0.25mm microaggregates in the sediment decreased by60%, while <0.002mm microaggregates was2-15times than that of the test soil.<0.002mmmicroaggregates decreased as rainfall and confluence intensity increased, the change of0.087-0.25mm was more complicated. Mean weight of specific surface area (MWSSA) andfractal dimension (D) of surface erosion decreased as rainfall and confluence intensityincreased. MWSSA and D of gully erosion increased with the increase of rainfall intensity, butit was opposite under confluence treatments. MWSSA and D could well reflectmicroaggregates losses.(4) Effects of surface and gully erosions on soil particles losses were explored. The lossamount of particles decreased in the order of silt> clay> sand, and the loss proportions ofthem were56%,37%and7%, respectively. Sand in the sediment was12%-62%lower thanthat of the test soil, while clay approximately increased9%than that of the test soil. Theimpacts of erosion patterns, rainfall and confluence intensity were not obvious to clay. D50ofgully erosion was generally greater than that of surface erosion, which indicated that sedimentparticles of gully erosion treatments were coarser than those of surface erosion treatments. D50could well reflect particles losses. The aggregate ratios of sand and silt (AR) in the sedimentwere greater than1, and AR of clay was smaller than1. This indicated that sand and silt weretransported as the original particles, while clay was transported as clay group.