Source And Transformation Of Nitrogen Pollutants In Zhengzhou Section Of The Yellow River Basin

The Zhengzhou section of the Yellow River Basin is one of the regions with rapid economic development in the Yellow River Basin,while its water body is faced a greater risk of nitrogen pollution load and water body eutrophication.According to the statistics in the past five years,nitrogen pollution was the primary pollution problem facing the water bodies in Zhengzhou section of the Yellow River.Therefore,by mastering the sources of nitrogen pollutants entering the Yellow River in Zhengzhou section and their seasonal changes,we can develop targeted control measures to reduce the risk of eutrophication in the water bodies.In this paper,four sampling sections are set up at the Yellow River Jiaozuo Yellow River Bridge（M1）,the Yellow River Huankou Yellow River Bridge（M2）and the Yiluo River at the Qilipu（T1）and the Qin River at Qushou.Based on pollutant flux,the composition of pollution source in main and tributaries is analyzed.Then the potential sources of nitrogen pollution in water bodies are identified by using the stable nitrogen and oxygen dual isotope traceability technique.Finally,nitrate nitrogen conversion pathways are identified based on nitrate concentration,δ¹⁵N-NO₃^-andδ¹⁸O-NO₃^-,and Illumina Miseq^TM/Hiseq^TMhigh-throughput gene sequencing of microorganisms is used to analyze the diversity and structural composition of denitrifying microorganisms in the Yellow River sediment,suspended sediment and overlying water during abundant water.The main findings are as follows:（1）The COD_Mn（permanganate index）,NH₄⁺-N（ammonia nitrogen）and TP（total phosphorus）in the main stream and tributaries of the Zhengzhou section of the Yellow River Basin have exceeded the standard in the last five years.The Huayuankou section of the Yellow River is a non-point source pollution type.The COD_Mn and TP at the Qilipu section of the Yiluo River are mixed type pollution,NH₄⁺-N and TN are point source dominant type.The COD_Mnand TP at the Qushou section of Qin River are non-point source dominant type,NH₄⁺-N and TN are mixed type pollution.（2）Nitrate nitrogen is the main nitrogen pollutant in the water body,and its concentration is significantly higher in the dry period than in the abundant period,and the tributaries are higher than the main streams.In addition,the nitrogen and oxygen isotopes of nitrate have more obvious spatial and temporal variation characteristics.In terms of time,the dry water period is more influenced by domestic sewage,resulting in higher average values ofδ¹⁵N andδ¹⁸O than the abundant water period.In terms of space,the tributaries are more influenced by domestic sewage and manure,resulting in higher average values ofδ¹⁵N andδ¹⁸O than the main stream of the Yellow River.（3）The seasonal variation of the proportion of different sources of nitrogen in the two sections of the Yellow River and the Yiiluo River is not obvious,in which the nitrate in the main stream section mainly comes from soil nitrogen upstream of the M1 section,with a contribution rate of 40%-46%;the tributary Yiililuo River section comes from domestic sewage and manure,with a contribution rate of 44%-47%.In contrast,there are seasonal variations in the tributary section of Qin River,with 45%contribution from domestic sewage during the dry period and40%and 37%contribution from soil nitrogen,domestic sewage and manure during the rich period,respectively.（4）Nitrogen and oxygen isotope signatures indicate that nitrification is the main microbial activity for nitrate transformation in Yellow River waters,and strong denitrification occurs in Yellow River sediments and overlying water.The diversity,species evenness and number of species of denitrifying microorganisms in suspended sediment during the period of abundant water are the largest.The dominant phylum of denitrifying bacteria in the suspended sediment and overlying water is Proteobacteria,ranging from 13.82%to 30.11%.The dominant genus of denitrifying bacteria in the suspended sediment and overlying water is Vogesella,3.33%-4.82%and 15.61%-20.70%,respectively.The dominant genus of denitrifying bacteria in the sediment is Bacteroides,ranging from 1.43%to 2.82%.