Influence Of Clay Minerals On Organic Carbon And Microbial Community In Channel Sediments

Minerals are important components of sediments solid phase,clay minerals are part of the most active inorganic colloids,which is the basis of fertility.The unique surface of clay minerals has the adsorption function for organic matter,active ions,microbial communities and some other substances.The sediment transfer in channel will affect the particle composition,and change the organic carbon content and microbial community structure.However,the influence of sediments clay minerals on the organic carbon and microbial communities is still unclear.Based on the main channel of Wangdonggou basin in Loess Plateau Gully Area,this study focused on bed load sediments and suspended sediments at gully head,upstream,midstream,downstream and checkpoint station.We adopted X-ray diffraction,high-throughput sequencing,qPCR and some other technical methods,conducted these following of research:（1）Distribution characteristics of organic carbon content of channel sediments from different basin locations.（2）Changes of clay minerals and active calcium ion and magnesium ion of channel sediments.（3）The relationship between the changes of channel sediments microbial communities and clay minerals.The following main results were obtained:（1）There is no significant difference in carbon content of bed load sediments in different basin locations,but what for suspended sediment is different.From gully head to checkpoint station,organic carbon（OC）content of suspended sediments shows an upward trend,with a decrease in silt particle content and an increase in clay particle content.The clay particle content of sediments is highly significantly positively correlated with the organic carbon content（p<0.01）,what is the key factor affecting nutrient content in particle composition.As the basin location changed,relative abundance of stable carbon isotope(δ¹³C)in sediments can remain stable,and there is no significant difference in the physical and chemical properties of the topsoil foundation.There is a significant difference between the relative abundance of channel sedimentsδ¹³C at the same basin location and the surface soil.（2）The crystal structure material in clay particle of suspended sediments is mainly clay minerals,the relative content of illite is close to 40%,chlorite and kaolinite can account for20%～30%,montmorillonite content is about 10%,and quartz can only account for about 3%.With the change of basin location,the relative content of illite in suspended sediments shows a downward trend,while the relative content of kaolinite and montmorillonite increase.The content of active calcium ion and magnesium ion in suspended sediments varies significantly at each basin location.From gully head to checkpoint station,the exchangeable calcium ion(Ca²⁺)and magnesium ion(Mg²⁺)content of suspended sediments shows an upward trend.The exchangeable Ca²⁺and Mg²⁺content is significantly positively correlated with OC and clay content in suspended sediments（p<0.01）.（3）From gully head to checkpoint station,the microbial community diversity and richness of suspended sediments show a downward trend,and the microbial community structure varies significantly in different basin locations（p<0.001）.The relative abundance of Proteobacteria and Ascomycota decreased by 7.7%and 9.3%respectively in suspended sediments,while Verrucomicrobia and Cyanobacteria increased by 8.2%and 5.5%respectively.The interspecific relationship of bacterial community tends to be complex,with enhanced community stability and anti-interference ability,while the above indicators of fungal community are opposite.With the change of basin location,the abundance of amyA,a functional gene related to starch degradation,and the activity of extracellular enzymes related to cellulose and hemicellulose degradation increase in suspended sediments.The microbial communities of suspended sediments are interrelated with nutrient content and particle composition,which can play an important role in the carbon cycle process and is related to the change trend of clay minerals.This study had clarified the change characteristics of clay minerals in channel suspended sediments with erosion transfer.In combination with the change trend of sediments organic carbon and microbial communities,we further analyzed and discussed the influence of clay minerals on them.This study can provide ideas for in-depth research on the impact mechanism of erosion transfer on sediments nutrient changes.