Study On Aggregate Stability And Organic Carbon Mineralization Characteristics In Erosional Gully Region

In order to reveal the impact of soil erosion on soil structure stability and organic carbon（OC）mineralization characteristics,and explore the effect of carbon source and sink in the forest under water erosion area,this paper selected the typical southern red soil hilly region-Qingyuan Mountain small watershed as the research area.According to the terrain factor,the surface is divided into top,up,middle and foot of the slope.The ¹³⁷Cs tracer technique is used to study the current status of soil erosion in eroded valleys in small watersheds and the dynamics of OC mineralization in aggregates.The research results are as follows:（1）The ¹³⁷Cs content at the top of the slope in erosional gully area is the highest,and is higher than the background value.It belongs to depositional area,while the up of slope and the foot of the slope are moderately erosional,and the mid of slope is slightly erosional.Soil erosion has a significant effect on soil physical and chemical properties.Nutrients are enriched in depositional area.In addition to OC,TN,and C/N ratio,other physical and chemical properties are significantly affected by slope position in erosional area.The erosional gully area shows absolute sedimentation,absolute erosion,relative sedimentation,and absolute erosion along the slope,and the topography factor is the dominant factor.（2）The content of macroaggregates in the depositional area was significantly higher than that in erosional area.Increasing erosion intensity led to the conversion of more macroaggregates to microaggregates,resulting in the soil aggregates in depositional area being more stable than erosional area,the up and foot of moderately eroded slopes above the mid of slope of light erosion.Secondly,soil erosion resulted in an even distribution of OC in each particle size in erosional area,while depositional area showed that the OC in macroaggregates was higher than that of microaggregates.Comprehensive aggregate index and physical and chemical properties index found that soil erosion has a direct effect and an indirect effect on the stability of the aggregate,in which the indirect effect is mainly reflected in the influence of the OC and related contribution rate of the 2-0.25mm aggregate,which ultimately affects the aggregate stability.（3）The rate of mineralization of OC in all soils and aggregates first increased in the early stage of culture（1-3d）,and then decreased rapidly until it stabilized.The cumulative mineralization in erosional area was lower than that in depositional area.The cumulative mineralization at the foot and up of the slope is higher than in the mid of slope.Soil aggregates are the main contributors to the mineralization of OC in the whole soil,mainly because the OC content and percentage of macroaggregates are higher than that of microaggregates,but the physical protection of macroaggregates is higher than that of microaggregates.In terms of protection,it is more susceptible to soil erosion.There are significant differences in the kinetic parameters of mineralization between erosional area and depositional area.Depositional area has a higher potential mineralization C0 value,a lower OC turnover rate constant k value and mineralization potential C0/SOC value.The kinetics of mineralization kinetics of OC in macro aggregates is similar to that in whole soils,while in microaggregates there are slight fluctuations.The mechanical composition of soil physical and chemical properties,capillary porosity,saturated water holding capacity,and C and N nutrients have significant effects on soil OC mineralization.In summary,soil erosion reduces the stability of the soil structure,leads to the loss of soil nutrients,and increases the risk of soil organic carbon mineralization.From the perspective of small watershed,soil erosion supports the view of carbon sources.The difference in mineralization characteristics of OC between erosional area and depositional area mainly depends on the level of background OC,that is,the OC redistribution caused by soil erosion;In the erosional area,the increase in erosion intensity increases the aerobic respiration of erosional area,increases the cumulative mineralization of the soil,and higher mineralization at the foot of the slope The amount and higher OC level are mainly due to the excitation effect of OC and the enrichment of sediment;the increase of anaerobic respiration in the deposition area also increases the mineralization of soil OC,regardless of whether it is an erosional or depositional areas,macroaggregates are the main contributors to soil OC mineralization.