The Research Of The Charcateristics Of Nitrogen Forms And Nitrogen-converting Microbial Community In The Surface Sediments In The Songhua River

The Songhua River is an important basin in China,and it is also the mother river for Heilongjiang and Jilin provinces.Nitrogen and nitrogen transformation related microorganisms are the important components of river ecosystem,and their distribution characteristics investigation could provide theoretical basis for river water-ecological restoration.Therefore,the nitrogen content,nitrogen morphological composition and nitrogen transformation related microorganisms of the surface sediments of the Songhua River whole basin in different river sections and flow periods were extensively studied in this paper,which could illustrate the spatio-temporal distribution characteristics of various morphological nitrogen and nitrogen transformation related microorganisms.The main results were shown as follows:The mean total nitrogen?TN?contents in the surface sediments of the Songhua River in the September normal river flow period and March dry season were 493.7 mg/kg and374.5mg/kg,respectively.The sequences of TN content in different parts of Songhua River were as follows:Songhua Mainstream?519.9 mg/kg?,Nenjiang River?512.5 mg/kg?and the second Songhua River?335.6 mg/kg?in the normal river flow period,and they were Nenjiang River?479.2 mg/kg?,Songhua Mainstream?379.4 mg/kg?and the second Songhua River?224.1 mg/kg?in the dry season.According to the EPA assessment criteria in US Sept.for sediment contamination and the guidelines issued by the Ministry of Environment and Energy of Ontario,Canada,there was no pollution risk of TN content in surface sediment of the whole Songhua River,but several samping sites exceeded alert values and attention should be paid to.The average contents of NH₄⁺-N,NO₃^--N and total organic nitrogen?TON?in the surface sediments of the Songhua River Basin in the September normal river flow period,i.e.92.5mg/kg,23.5 mg/kg and 377.6 mg/kg,were higher than those in the Mar.dry period,i.e.76.8mg/kg,19.6 mg/kg and 278.1 mg/kg.The NO₂^--N content were low and no obvious difference for the two river flow periods.The highest NH₄⁺-N average content of the two periods were both in the Nenjiang River reach of Songhua River,and the highest average NO₃^--N and TON contents of the two periods were all in the Songhua River Mainstream.Ammonia-oxidizing bacteria?AOB?amoA genes were 9.0×10⁷ copies/g·soil and 1.2×10⁸copies/g·soil in the normal river flow period and dry season for the whole Songhua River,and Ammonia-oxidizing archaea?AOA?arch-amoA genes were 1.8×10⁷ copies/g·soil and 8.9×10⁶copies/g·soil accordingly.The amo A genes content was higher than the arch-amoA genes,and the genes in the normal flow river period were higher than those in the dry season.The amoA gene contents succession of different reaches of Songhua River were as follows:the Second Songhua River?1.1×10⁸ copies/g·soil?,the Songhua River Mainstream and Nenjiang River,and the arch-amoA gene quantity were almost the same for different Songhua River sections,which order from high to low were Nenjiang River?2.8×10⁷ Copies/g·soil?,the Songhua River Mainstream and the Second Songhua River.In the dry season,the amoA genes and arch-amoA genes content sequences were as follows:the Second Songhua River?2.3×10⁸amo A-copies/g·soil and 1.7×10⁷ arch-amoA copies/g·soil?,the Songhua River Mainstream and Nenjiang River.The denitrification functional gene contents sequences of the Songhua River in Septembe normal river fiow period were shown as follows:nirS?8.3×10⁷ copies/g·soil?,nar G?1.9×10⁷ copies/g·soil?,nirK?8.4×10⁶copies/g·soil?and nosZ?1.7×10⁶ copies/g·soil?.The nirS gene succession of different Songhua River parts were listed as follows:the Songhua River Mainstream?9.0×10⁷ copies/g·soil?,Nenjiang River and the Second Songhua River,and the order of narG and nirK were shown as Nenjiang River?3.4×10⁷ copies/g·soil,1.0×10⁷copies/g·soil?,the Songhua River Mainstream and the Second Songhua River.The order of nosZ content from high to low were illustrated as:the second Songhua River section?2.4×10⁶copies/g·soil?,the Songhua River Mainstream and Nenjiang River.The denitrification functional gene contents sequences of the Songhua River in March dry season were shown as follows:nirS?2.4×10⁸ copies/g·soil?,nirK?2.3×10⁷ copies/g·soil?,nosZ?1.7×10⁶copies/g·soil?and narG?1.4×10⁶ copies/g·soil?.The nirS gene succession of different Songhua River parts were listed as follows:the Songhua River Mainstream?2.3×10⁸copies/g·soil?,the Second Songhua River and the Nenjiang River,and the order of nirK and nosZ were shown as the Second Songhua River?3.1×10⁷ copies/g·soil,2.5×10⁶copies/g·soil?,the Nenjiang River and the Songhua River Mainstream.The order of narG content from high to low were illustrated as:the Nenjiang River?1.9×10⁶ copies/g·soil?the Second Songhua River and the Songhua River Mainstream.The community abundance of AOB amoA genes in the normal river fiow period and dry season?30%-44%?were higher than those of the AOA arch-amoA genes?2.3%-11%?,and the denitrifying nirS genes were both dominated in the two river water periods.The nirS genes abundance?61%?in the dry season was higher than that in the normal river flow period.Correlation analysis of environmental factors and microorganisms were shown as follows:the AOA genes were only positively correlated with NH₄⁺-N during the normal flow river period,and the AOB and narG genes were positively related with TN,NH₄⁺-N,TP and the water content of the sediments.The nirS and nirZ were positively correlated with TN,NO₂^--N,TON,TP,pH and the water content.Howerver,the narG and Arch-amoA were negatively and obviously related with pH,and the similar negative correlation for the nirK with NO₃^--N and NH₄⁺-N?P<0.01?.There was no significant correlation between environmental factors and microorganisms related to nitrogen transformation in dry season.In the nitrification stage,pH was positively correlated with AOA genes,and negatively correlated with AOB genes.