| Soil erosion has become a severe environmental and social issue throughout the world.Karst landscape represent an important facet of the earth’s geodiversity.Underground double layer space structure and bedrock bareness are the main factors that lead to complicated mechanisms of soil erosion in karst regions.In order to deeply understand the characteristics of water and soil erosion under different surface crops of karst area,based on the field investigation,according to the surface and underground double layer space structure in the karst region to design the experiments,selection of vegetable land,grassland and bare land in three types of land use as the main research object,under natural rainfall conditions,observation data from surface runoff,sediment erosion and underground leakage of water and sediment were analyzed by quantitative methods,during the experimental period.This paper research on the characteristics of soil and water loss by quantitative methods and the characteristics of soil nutrient loss by laboratory experiment under different surface crops,which is vegetable land,grassland and bare land in Karst.These can provide theoretical and practical significance for understanding soil erosion mechanisms and controlling soil and water loss in karst regions.The results show:(1)From August to November in 2016,the total precipitation reached 445.58 mm.During the period of experiment,the precipitation of November was minimum,which was only occupied14% of the total rainfall,but the precipitation of September was the maximum,accounted for 41% of the total rainfall,in August and October,the total rainfall was not different,respectively accounted for 22% and 23% of the total rainfall.During the experiment,the days of light rains were the most,but the precipitation accounted for only 19.31% of the total rainfall;the days of moderate rain were 11 days,but the rainfall was accounted for 42.71% of the total rainfall;the days of heavy rain were although only three days,but the rainfall accounted for 24.04%.There was only a rainstorm,occurring at the end of August,with the characteristics of the heavy precipitation,the high rainfall intensity and the strong rainfall erosivity.The rainfall erosivity of monthly was the strongest in September,reaching 1036.98MJ·mm/(hm2·h).The largest of daily rainfall erosivity occured in August 29 th,reaching 25.3MJ·mm/(hm2·h).(2)The characteristics of soil and water loss of different surface crops are not identical.Overall,during the experiment,the leakage of water through the underground pore fissures was more than surface runoff.The surface runoff and the leakage of water through the underground pore fissures varied with the change of the rainfall,rainfall intensity,and the loss of surface runoff and the leakage of water through the underground pore fissures were presented the trend:bare land>grassland>vegetable fields.But when it was small rainfall,light rainfall intensity,the surface of soil layer was not easy to produce runoff and not going to produce the surface soil and water loss,at the same time,the rain went into the soil,becoming to be the formation of soil grains and then seeping into the underground through underground pores,cracks and so on,at last,under the double action of water and gravity,producing the underground soil loss.But when the rainfall,rainfall intensity increased into a certain extent,surface runoff,runoff distribution ratio increased with the increasing of rainfall intensity and runoff coefficient,but the leakage of water through the underground pore fissures,with the increasing of rainfall intensity,distribution rate decreased,the surface runoff was greater than the underground pore fissure runoff.(3)Soil erosion in the karst area has two forms:soil erosion of the earth’s surface and underground pore fissure soil loss,which is the one important characteristics that is different from the not kast area.In terms of sediment of erosion,which is closely related to the runoff.The results of studies show that during the experiment,three surface crops,the leakage sediment of underground was greater than the total sediment flow on the surface of the earth,the surface sediment showed the characteristics that bare land > vegetable fields> grassland,and in the ground,soil loss of bare land was the biggest one,but the grass land and vegetable fields had not a big difference.(4)Secondary rainfall had an important influence on soil erosion.Under the same surface crops,different rainfall intensity,soil and water loss were different.Under the same rainfall intensity,different surface crops,soil and water loss were also different.(5)In terms of total nutrient loss,underground was greater than the surface.The nutrient loss of bare land was the most serious and the nutrient loss of vegetable fields was greater than the grass land.Hydrolysis of nitrogen loss was seriously,compared with available potassium and available phosphorus.The underground loss of available k was much larger than the surface.In addition,under different surface crops,most of the underground leakage of soil particles fractal dimension was greater than the surface erosion of soil,the higher the fractal dimension,the greater the coarse particles volume fraction,which suggested that the study area the surface erosion of soil particle size was greater than the underground leakage of soil particle size,but this was not absolute,it had a lot of relevance with rainfall,rainfall intensity and so on.(6)Rainfall,rainfall intensity,rainfall erosion force had a high correlation with underground pore fissure water and sediment.But correlation coefficient of the underground sediment leakage with rainfall intensity was higher than with correlation coefficient of rainfall.Besides,to the correlation coefficient of the underground sediment leakage with the underground water loss,bare eland was greater than the vegetable,the grass was the lowest.(7)Under the different surface crops,surface runoff and surface sediment erosion directly show good linear relation,and the fitting was also very good,while the underground water loss and underground soil leakage could not be presented a good linear relationship. |
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