Carbon And Nitrogen Loss Process In Soil-epikarst System On A Karst Hillslope

The heterogeneity of surface soil and exposed rock in karst slopes and the diversity of underground rock fractures make the hydrological processes on sloping lands in karst areas unique and complex.In this paper,traditional hydrological observation methods are used in conjunction with automatic slope runoff monitoring equipment.Hydrogen and oxygen stable isotope tracer techniques are used to continuously monitor the three-dimensional production process of arable land on bare slop under natural rainfall conditions,and to study the different runoff paths of arable land on karst slopes.this study conducted rainfall induced runoff and carbon-nitrogen loss monitoring during monsoon in Karst bare slopes,Isotope-based(D and ¹⁸O)hydrograph separation method was applied to partition the ratio of‘old'and‘new'water in main hydrological path,and initially analyzed the source of runoff water.The research on the characteristics of rainfall infiltration and runoff and the characteristics of nutrient migration in karst slopes can greatly promote the development of hydrology in karst slopes.It is of great scientific significance to deepen the understanding of rational allocation of water resources on scale and loss and control of nutrient loss in slope land.The main results are as follows:?1?In different rainfall events,there is a delay effect in the volumetric water content of the soil responding to the peak value of the rainfall.During the rainfall events of June 6,June 15 and June 28,the volumetric water content of the soil basically reached an extreme value around 1 h,while in the rainfall event of July 10,the peak value of the soil moisture amount was delayed by about 6 h in response to the peak rainfall time.In addition to the?D and?¹⁸O values of the surface runoff on June 6 and the values of?D and?¹⁸O of rain,the values of?D and?¹⁸O in surface runoff and the value of?D and?¹⁸O in rain during the other three rainfall events are very different.?2?By comparing the rainfall events of different previous soil moisture contents,it is shown that the enrichment of stable hydrogen and oxygen isotopes in surface runoff is relatively large,and with the gradual increase of soil moisture,stable hydrogen and oxygen isotopes in surface runoff are depleted.And it gradually approaches the value of the stable isotopes of hydrogen and oxygen in the interflow and deep percolation.Moreover,by dividing the ratios of old and new water in different hydrological routes by using?D and?¹⁸O values,it was found that surface runoff“new water”accounted for 70%,while in the interflow and Deep percolation,the“old water”dominated the proportion of“old water”.It is 65%and 70%respectively.Comparing the changes in the ratio of“new water”in different hydrological paths with less soil moisture?June15th?and higher water content?June 28 and July 10?,it can be seen that the“new water”in the early surface runoff"There is a very high proportion?about 95%?,and the proportion of"new water"in the interflow and deep percolation is very small?about20%?,but the"new water"changes in the interflow and deep percolation are similar.?3?The results of the study found that the interflow and deep percolation are the main forms of runoff from rainfall infiltration,accounting for about 82%of the total runoff.During the course of rainfall,the characteristics of carbon and nitrogen losses in different hydrological pathways performed differently,but the carbon and nitrogen losses all showed:deep percolation>interflow>surface runoff.In addition,the difference of carbon and nitrogen loss in different hydrological paths was significant.The total carbon and nitrogen loss in the deep percolation and the contribution rate were significantly different from those in surface runoff and interflow,but the difference between the total amount and contribution of ammonium nitrogen and total nitrate nitrogen and total nitrogen of the interflow and surface runofftotal is not significant.