| The south-east karst area of China,which is restricted by special karst geological background is a typical ecologically fragile area with serious water and soil loss,frequent flooding and high risk of groundwater pollution.The karst ecosystem is composed of a complex combination of heterogeneous microhabitats(including rock,soil surface and soil-rock microhabitats).The understanding of the soil and water process of each microhabitat is the premise of understanding the mechanism and process of the confluence and the migration of biomass on karst slope.However the study about this is insufficient.Due to the complex surface morphology,the small habitats are more fragmented in this area,the hydrological processes in karst region are highly variable in space and time,with stong karst effect.To explore the differences of hydrological characteristics between different habitats and the characteristics of nutrient loss and erosion process under hydrological drive,can provide basis for the treatment of rocky desertification,and can also provide scientific support for flood disaster and surface source pollution control in karst area.In this paper,different karst microhabitats in northwest Guangxi were selected as the research object,and rainfall simulation technology in field was combined,to clarify the differences of hydrological features and nutrient losses progrecsses among different microhabitats.The broken habitats were classified considering the different morphological characteristics among these microhabitats.On account of the viriable characteristics amomg different microhabitats,the characteristics of rainfall and runoff between different habitats were thrown light on,and the features of nutrient loss and sediment erosion for different habitats under hydrological drive were revealed,then,the model of nutrient loss law was fitted,and the sediment process of different habitats were investigated combining with the chemical index of hydration,the main results are as follows:(1)Outcrop runoff in karst area was the main pattern to runoff,with high runoff coefficient(0.50±0.19,0.49±0.21,0.70±0.17)under circumstance of 20,50,70mm/h rainfall intensities,which the average infiltration rates were 11.28,23.01 and 19.24 mm/h,respectively.And the soil interface had high infiltration rate,which the average infiltration rate of rainfall intensity at 20,50,70 mm/h were 15.98,44.55,38.01mm/h,and the surface runoff coefficient was low.The average infiltration rate of rainfall intensity at 20,50,70mm/h in soil habitat were 15.98,44.55,38.01mm/h with high infiltration performance,and the surface runoff coefficients were low(0.21±0.33,0.15±0.19)in medium and small rainfall intensities,then subface flow and deep infiltration were the important hydrological path,however,when it was the high rainfall intensity,overland flow occupied the mian part of hydrological process.The impact of antecedent moisture on soil interface microhabitat was more than rock interfance microhabitats,the overland flow was little,even non-existen under dry condition.Overland flow dominated in rock-soil microhabitat,runoff at rock-soil interface was a kind of preferential flow to supply interflow and deep infiltration.(2)The nutrient concentration of overland flow was high during the initial stage of precipitation resulting from the first flush effect among rainfall-runoff processes of all the microhabitats,and then the concentration reduced to a stable level with the increase of the runoff amount.And the rainfall intensity can affect the runoff generation,and as the rainfall intensity increased the nutrient loss flux gradually increased.The nutrient loss of carbon and nitrogen was minimal in soil microhabitat under the conditions of medium and small rainfall intensity(20,50mm/h),under the conditions of high rainfall intensity(70mm/h)the nutrient loss of carbon and nitrogen had a significant increase in overland flow.Becouse of huge amount of overland flow,the outcrop microhabitat and rock-soil microhabitat were the major area of rainfall-runoff process in karst region,and the plant-covered rock microhabitat was the important part of TOC loss.(3)The exponential function and power function can effectively match the process of carbon and nitrogen nutrients loss.The ratios of C/N in overland flow were lower(1.72 and 1.00)in the rock-soil microhabitat and the soil microhabitat,while the carbon and nitrogen ratio of the plant-covered rock microhabitat and bare rock microhabitat was 3 to 10 times that of the former.(4)There was a significant linear relationship between turbidity and sediment,and the turbidity can reflect the sediment concentration to a certain extent.The sediment processes in overland flow were the most obvious in soil interface microhabitat and rock-soil microhabitat,and the sediment erosion mainly occured between these two habitats.(5)There were differences in erosion process of soil surface on hillslope under different rainfall intensities conditions,the sediment yield was low under medium and small rainfall intensity conditions,and the surface sediment is obvious under high rainfall intensity condition.There was an increasing trend of sediment erosion on the slope,and the erosion modulus showed that the upper and lower slopes were smaller,and the slope erosion modulus was 15 times larger than that of the middle slope.The difference in the erosion process of rock-soil under bare rock rates was obvious.With the increase and decrease of the bare rock rate,the erosion modulus increased firstly and then decreased,and the erosion modulus was the largest at the 50% bare rock rate. |
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