Study On Redox Zoning In River Infiltration Zone Under The Influence Of River Bed Siltation

The interaction between surface water and groundwater has always been an important content in the study of terrestrial hydrological cycles.In the process of river water infiltration,especially when the mining by the river stimulates the infiltration of river water,river bed sediments as an important zone and key interface for the interaction between surface water and groundwater have obvious physical,chemical and biological gradients.As a result,strong biogeochemistry occurred,forming vertical redox zoning of river bed sediments.Due to the seasonal changes of river hydrodynamic conditions,the river bed will have different degrees of siltation in different periods,and the structure and lithology of the river bed sediments will also change.By affecting the infiltration rate of the river water,it will affect the river water deposition The residence time in the sediment caused the redox zoning in the river bed sediment to change.The redox zoning of river bed sediments during river infiltration has a great influence on groundwater quality.At present,the mechanism by which river siltation affects the redox zoning of river bed sediments is unclear,and the characteristics of redox zoning in river bed sediments need further study.Based on this,this paper selects the Liaohe River bed near the groundwater source of Huangjia groundwater in Shenyang as the research object,collects river bed sediment and pore water samples at different points on a typical profile,and analyzes the structure and lithology of the river bed sediment at different points Characteristics,combined with river hydrodynamic conditions,to divide the silting zoning,using thermal tracing method to calculate the hydrodynamic characteristics of river water infiltration in silt layer formed by silt,reveal the change rule of river bed sediment redox zoning under the influence of silting,analysis the microbial composition and function differences of riverbed sediments under the influence of siltation,reveal the response characteristics of microbial composition to redox zoning,and provide a scientific basis for ensuring the safety of water supply in rivers and drinking groundwater.Through this study,the following conclusions were obtained:(1)Along the direction of the groundwater mining funnel along the river,the cross section of the river bed perpendicular to the flow direction of the Liaohe River is controlled by the dynamic conditions of water and sediment,and there are obvious siltation zones in the river bed sediments.The section with weak water and sand dynamic conditions in the range of 0 ~ 40 m from the south bank of the Liaohe River is a strong siltation zone of river bed sediments,and the thickness of the sediment surface silt layer is greater than 50 cm.Within the range of 40 ~ 125 m from the south bank of the Liaohe River,it is a medium silt zone.There is a silty layer on the surface of the sediment,and the thickness is less than 50 cm.The strong range of water and sand dynamic conditions 125 m away from the south bank of the Liaohe River is the weak silt zone,the river flow velocity is large,and there is almost no silt layer on the surface of the sediment.(2)During the monitoring period(from September to November 2019),due to the gradual decrease of the river's sediment content,the sedimentation of fine particulate matter in the river began to decrease,and the permeability of the river bed sediment gradually increased over time,indicating the siltation of the river bed sediment The role gradually weakened.(3)The results of redox zoning of sediments indicate that O2 / NO3-reduction zone,Mn(?)reduction zone,Fe(?)reduction zone and SO42-reduction zone exist in order from top to bottom within 50 cm of the surface layer of river bed sediments.Affected by the degree of siltation,there are obvious differences in the extent of redox zoning extension of riverbed sediments in different silt zones.The zoning sequence of the strong siltation zone is relatively complete,forming the O2 / NO3-reduction zone,the Mn(?)reduction zone,the Fe(?)reduction zone,and the SO42-reduction zone,while only O2 /NO3-reduction zone and Mn(?)reduction zone appears in the medium and weak siltation zones.(4)The results of molecular biology tests on river bed sediments show that there are obvious differences in the composition and structure of microorganisms in different redox subzones,which is manifested in the relatively high abundance of exclusive reducing bacteria controlling redox in each subzone.Among the microbial populations in the river bed sediments,amino acid transport and metabolism,carbohydrate transport and metabolic functions have a higher abundance of microorganisms,indicating that the geochemical action of carbon and nitrogen elements in the sediments is very active.The differences in sedimentary microbial functions are significant,and they respond well to biogeochemical types.