| The anaerobic ammonium oxidation(Anammox)process is a research focus of the nitrogen cycle in recent years.This process not only plays an important role in the nitrogen loss of natural ecosystems,but also in the nitrogen removal treatment of wastewater.Coastal ecosystems which located in the interlaced zone between land and ocean,are heavily affected by human activities,and are also important sites for the Anammox process.At present,studies on Anammox mainly focused on the wastewater treatment process and some anaerobic natural environments.However,the research on Anammox bacteria and its response to environmental stress in the coastal zone are rarely documented,especially the effects of different organic pollutants on Anammox bacterial community and function in the coastal zones of Hainan has not been reported before.The coastal zone of Hainan is located in the tropical and subtropical area,which is an ideal place to study the marine nitrogen cycle.In this study,three typical coastal zones in Hainan(Yangpu Bay,Dongzhai Harbor and its intertidal zone,and Bamen Bay)were selected as study areas.Organic pollutants in sediments from these areas were indentified and quantified by using trace/ultra-trace non-target compound screening analysis;and the community structure and abundance of Anammox bacteria were studied by molecular biology techniques;Yangpu Bay was then selected to study the Anammox rate and contributions to the nitrogen loss by stable isotope tracing technique.What’s more,the main environmental factors affecting the ecological distribution and function of Anammox bacteria in sediments of Hainan coastal zone were explored,and the response mechanism of Anammox bacteria to these factors were clarfied.The main findings are as follows:(1)Different types of organic pollutants were detected in sediments from different coastal zones by using non-target compound screening analysis.Totally,114,84,75 and 58 kinds of organic pollutants were detected in Yangpu Bay,intertidal zone of Dongzhai Harbor,Dongzhai Harbor and Bamen Bay respectively.These organic pollutants were polycyclic aromatic hydrocarbons(PAHs),organochlorine(DDT)and its metabolites,organotin compounds,monoaromatic compounds and their derivatives,and halogenated compounds.The concentrations of three main types of organic pollutants(PAHs,DDTs,organotin compounds)in sediments from different regions were quite different.The total concentration of PAHs was the highest,followed by DDTs and organotin compounds.The average concentration of ∑PAHs was highest in Yangpu Bay(1643.4 ng/g),and the lowest in the intertidal zone of Dongzhai Harbor(98.3 ng/g);the average concentration of∑DDTs was highest in Bamen Bay(226.0 ng/g),the lowest in Dongzhai Harbor(1.2 ng/g);the average concentration of total organotin compounds was highest in Bamen Bay(178.2 ng/g),the lowest in the intertidal zone of Dongzhai Harbor,with 2.5 ng/g.Compared with other coastal zones in the world,PAHs and organotin compounds in this study were at the moderate pollution level,while DDTs was at the high pollution level.Risk assessment showed that the potential ecological risks of PAH individuals and total PAHs exist in all three regions,and the biological effects on local organisms may occur frequently.Compared to Dongzhai Harbor,the ecological risks in Yangpu Bay and Bamen Bay were more serious.p’-DDT,p,p’-DDD and p,p’-DDE and total DDTs may have frequently adverse effects on the local environment of all three regions.Yangpu Bay and Bamen Bay were more seriously affected by this type of pollutants.The concentrations of TBT in parts of Yangpu Bay may have harmful effects on local ecosystem,and the other areas in this study were relatively safe.In addition,high concentrations of tetraphenyltin and other types of organotin compounds detected in Yangpu Bay and Bamen Bay were unable to carry out ecological risk assessment due to lack of relevant biological effects data,but their potential ecological risks need to be taken seriously.(2)Anammox bacteria were detected in all sediment samples from the three typical coastal zones in Hainan by Anammox bacterial 16S rRNA gene clone library.The diversity of Anammox bacteria in the study areas was quite high,among which Anammox bacterial diversity in Yangpu Bay was the highest,followed by Bamen Bay,Dongzhai Harbor,intertidal zone of Dongzhai Harbor.The known dominant genera of Anammox bacteria detected in the three regions were Candidatus Scalindua,Candidatus Kuenenia and Candidatus Brocadia.The intertidal zone of Dongzhai Harbor was dominated by Kuenenia,while the other areas were characterized with iScalindua.The community structures of Anammox bacteria in the different three regions were quite different.In Yangpu Bay,Scalindua was the most dominant genus,followed by Brocadia and Kuenenia;in Dongzhai Harbor and Bamen Bay,Scalindua was also the most dominant genus,while followed by Kuenenia and Brocadia;in the intertidal zone of Dongzhai Harbor,only Kuenenia and Scalindua were detected,and Kuenenia was the dominant genus.Correlation analysis showed that the main environmental factors affecting the community structure and distribution of Anammox bacteria in different regions were different.In Yangpu Bay,Anammox bacterial community structure was mainly affected by the contents of nitrite,total organic carbon,PAHs and DDTs.In Dongzhai Harbor,the main influencing factors were pH,temperature,salinity,water depth,total phosphorus,active phosphate and total organic carbon and PAHs in sediments.In the intertidal zone of Dongzhai Harbor,Anammox bacterial community was mainly affected by ammonia,nitrite and total organic carbon in sediments.In Bamen Bay,the main influencing factors were pH,salinity,conductivity,water depth,Prometryn,Galaxolide,ammonia,nitrite and nitrate in sediments.It is indicated that the community structure and ecological distribution of Anammox bacteria are affected by mixed environmental factors in the natural environment.(3)The results of fluorescence quantitative PCR showed that Anammox bacterial 16S rRNA gene and hzsB functional gene abundance in different coastal zone were quite different.The average abundance of Anammox bacterial 16S rRNA gene was highest in Bamen Bay(60.0×105 copies/g),and lowest in the intertidal zone of Dongzhai Harbor(22.7×105 copies/g);the hzsB functional gene of Anammox bacteria was highest in Bamen Bay(45.4×105 copies/g)and lowest in Yangpu Bay(32.6×105 copies/g).The main environmental factors affecting the abundance of Anammox bacteria in different regions were different.In Yangpu Bay,nitrite,PAHs and DDTs in sediments were the main influencing factors.In Dongzhai Harbor,pH,depth,nitrite,nitrate of water,and nitrite,total organic carbon in sediments were the important environmental factors.In Bamen Bay,the main influencing factors were ammonium,nitrate in sediments and prometryn.It indicates that the abundance of Anammox bacteria in the coastal zone is also affected by various environmental factors.(4)According to the previous results,the number of organic pollutants detected in Yangpu Bay was the highest,and the concentrations of these organic pollutants were quite higher than other areas.Therefore,Yangpu Bay was selected as a representative area to study the anaerobic ammonium oxidation reaction activity.Based on the stable isotope tracing technique,it was found that the activity of Anammox reaction was detected in some areas of Yangpu Bay,and the average rate of anammmox reaction was lower than the denitrification rate,and the contribution to the nitrogen loss was also lower than denitrification.The rate of Anammox reaction was in the range of nd-6.21 nmol/g/h,and the average rate was 1.81 nmol/g/h.The contribution of Anammox reaction to total nitrogen loss ranged from 0 to 34.4%,with an average value of 8.5%.The denitrification rate ranged from 9.62 to 42.52 nmol/g/h,with the average rate of 24.04 nmol/g/h.It indicates that the nitrogen removal process was dominated by denitrification in sediments of shallow coastal areas.The main environmental factor affecting the rate of Anammox reaction in Yangpu Bay was pH of water.No other environmental factors were found to be significantly correlated with the reaction rate.(5)Based on the structural equation model(SEM),it was found that the response mechanism of Anammox bacteria to environmental factors in different coastal zones was different.In general,ammonium,nitrite and nitrate in sediments were the most important environmental factors affecting Anammox bacteria.hzsB functional gene of Anammox bacteria can be affected directly and indirectly by PAHs,DDTs and Galaxolide.All of the three pollutants have influence on the diversity and 16S rRNA gene abundance of Anammox bacteria,and further affect the hzsB gene expression.In addition,water depth,pH,ammonium,nitrite,and nitrate have direct effects on the pH,dissolved oxygen and the substrate concentration required for the Anammox reaction in sediments.The changes of these factors directly affect the diversity of Anammox bacteria and its 16S rRNA gene abundance,and functional genes,which have further impact on the nitrogen removal efficiency of Anammox bacteria. |
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