| Most of rivers in China are sandy.As carriers of chemical matter and microorganism,solid particles play an important role during material,energy and information exchange between land,surface water and sediment,which are also important participants in the geochemical process of river basin.For the complexity and diversity of river sediment sources,and the sediment migration is often accompanied by changes in physical and chemical properties between different habitats,the microbial ecological impact caused by particulate matter is difficult to be clearly understood.This study focuses on “river sediment–water–microbial ecological effect” and choose the Weihe River(Shaanxi section)as the representative of seasonal sandy river.First of all,suspended particle,surface water and sediment were sampled in three different hydrology period to reveal the spatial-temporal variation rules of dissolved and particle-associated organic matter,nitrogen and phosphorus,as well as sediment influence on river water quality change.On this basis,the bacterial community in water and sediment were characterized by using Terminal restriction fragment length polymorphism(T-RFLP)technology and 16 S rRNA amplicon sequencing on Illumina Miseq platform.Then the key environmental driving factors of bacterial communitiy in different hydrological period were identified by CCA/RDA,and the contribution degree of particulate matter characteristics on water and sediment bacterial community change were also calculated.Considering the important role of particulate matter during land-river communication,bacteria community composition and diversity in three kinds of habitat,including riparian soil,surface water and sediment were characterized and compared by Bray-Curtis similarity and ternary diagram.Finally,the influence of sediment change on river water quality and bacterial community diversity was systematically elucidated.Relevant results could provide theoretical basis for the protection and management of water ecological environment in seasonal muddy rivers.Main results are as follows:(1)The total suspended solid concentration in the Weihe river basin(Shaanxi section)varied between 0.003g/L~16.332g/L.and the mean value in main stream during the wet season is 23 times that in the normal and 58 times that in the dry.Suspended particles in wet season are mainly clay and fine silt(d(0.5)=7.34 micron).Rainfall floods from upstream and north tributaries,agricultural non-point sources in Guanzhong basin,urban municipal sewage and rainwater runoff are the main sources of TSS in Weihe river(Shaanxi section).Their relative contributions in different hydrological seasons determine the spatial variation rules of TSS concentrations.During the wet season in 2014,sediment was deposited in the Baoji section,then combined erosion and sedimentation in the Xianyang-Xi'an section,and finally deposited again in the Weinan section after receiving the sand from the north tributaries.The spatial difference of sediment particle size is caused by the change of sediment erosion and siltation in different river reaches.(2)TN and TP content in flood sediment was 11.28g/kg and 5.31g/kg from upstream,while 8.21g/kg and 4.65g/kg from north tributaries.These exogenous particles make the proportion of particle-associated COD,TN and TP in surface water raised to 49.3%,40.8% and 98.8%,which was 9,59,and 15 times of other two period.Meanwhile,proportion of dissolved complex organic matter and dissolved organic nitrogen were also increased.RDA analysis results indicated that TSS is an important explanatory factor for water quality change in different periods,which can independently explain 28.1%(normal),2.0%(dry)and 7.3%(wet)comprehensive water quality change.The influence of suspended particle concertration and TN,ammonia nitrogen content on water quality spatial change is more significant than particle size characteristics in wet season.Flood process,sediment behavior and the land use pattern of river basin shape the spatial pattern of Weihe River water quality in different hydrological periods.(3)The Shannon diversity of bacterioplankton community changed between 1.42~2.91,while the order of spatial mean value of the three seasons is wet > normal >dry.The seasonal variation of bacterioplankton community structure is greater than the spatial variation.There existed a consistent “core bacterial community” including many functional species which can degrade river pollutants,indicating the potential self-purification ability of the Weihe river water body.TSS,dissolved TP and C/N ratio are the key driving factors for the variation of bacterioplankton communities in Weihe River during different hydrological seasons.Independently,the TSS can explain 12.5%,23.5% and 9.4% bacterial community changes in normal,dry and wet season respectively.Proteobacteria(46.7%~56.4%)and Bacteroidetes(27.2%~33.4%)was the dominant Phylum of bacterioplankton community in high sediment load river water during wet season.Betaproteobacteria was most abundant in Proteobacteria,while the abundance of delta-proteobacteria(4.99%~6.29%)and epsilon-proteobacteria(0.98%~ 7.72%)is higher than that of most other surface waters.During the wet season,the bacterioplankton community was most sensitive to the volume ratio change of 32-63?m particles,and different communities had special preference to different particle size range.The concentration of TSS was significantly relative with function bacterial group or indicator bacterial group associated to rainfall flood,agricultural non-point source and urban pollution source in wet,normal and dry season.The presence of particulate mat ter plays a positive role in increasing the proportion of function bacterial community and act as a carrier for terrestrial microbial genetic information in wet season.(4)The sediment bacterial community Shannon diversity changed from 1.05 to 3.18,which was higher than that of phytoplankton community except in the wet season.The NMDS analysis indicated that bacterial communities separated into two types of habitats,surface water and sediment,in different hydrologic seasons.And it also showed different seasonal and spatial succession directions between sedimental and suspended bacterial communities.The dominant species of sediment bacterial community were more abundant during wet season(dominant T-RF rised from 21/26 to 31),and the complex scouring-silting process increased the spatial difference of sediment bacterial community composition and diversity.Due to coarse particle size and high pressure of heavy metal pollution,the diversity of bacterial community in Xi'an section(2.37)was the lowest of mainstream in normal season,and the dominant T-RF fragment with metal tolerance appeared.During the dry season,the sediment particles provided shelters for pathogenic bacteria in Xi'an section and cause long-term health risks for downstream water bodies.The results of multivariate direct gradient analysis showed that,among many environmental factors,the influence of nitrogen and phosphorus content as well as particle size characteristics of sediments on the change of bacterial community was most prominent in normal and dry season.(5)The diversity of riparian soil bacterial community was higher than surface water and sediment in Weihe River basin during the wet season.The phyla of bacterial communities in the three habitats are very similar,but the relative abundance is different,and the difference is more sufficient at the lower level.The bacterioplankton community and soil bacterial community showed higher Bray-Curtis similarity at different classification levels.Ternary diagram analysis showed that relative abundance of Epsilonproteiobacteria and Sphingobacteria in surface water was significantly higher than that of the other two types of habitats,while Bacilli,Bacteriodia,Clostridia,Synergistia and Themoleophilia showed higher abundance in the sediment samples,and Nostocophycideae,Synechococcophycideae,Spartobacteria,Chloracidobacteria and Solibacteres showed higher abundance in the river soil samples.there were unique high abundance species in all three habitats,and the unique group types in sediments and soil were more abundant than those in surface water.Rainfall flood with terrestrial material and resuspension of sediment is beneficial for keeping the rare species in Weihe River channel.Soil could make more contribute to the stability of bacterioplankton community structure comparing to sediment.The nitrate content and particle size characteristics of particulate matter could explain the 65.5% change of bacterial community among the three habitats in the study area.Particle size diversity and median particle size are the most critical factors in chosen particle characteristic index. |
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