| Since the last century,the growing demand for marine food from population growth has stimulated the development of marine aquaculture.Marine aquaculture is one of the most important activities in the tropical and subtropical coastal regions.Due to poor planning and management and lack of appropriate regulations,a large amount of wastewater rich in nutrients and aquaculture antibiotics were discharged directly into adjacent coastal areas and had adverse environmental impacts on coastal ecosystems.During the high-level aquaculture activities in southern China,wastewater with a large amount of nitrogen nutrients was discharged into adjacent mangroves,but the effect of wastewater on the functional microbial communities and N2O production in the mangroves was still unclear.Therefore,the project studied the time dynamics and mechanism of N2O emission in mangrove sediments and studied the mechanism of the effect of antibiotics which were the most concerned pollutants in aquaculture wastewater on N2O production in sediments.This will help to further understand the contribution of mangrove wetlands caused by aquaculture to the atmospheric greenhouse effect and provide guidance for marine environmental protection,national greenhouse gas inventory calculations and the protection of mangrove wetlands.(1)The N2O flux and sediment characteristics of mangrove sediments and the microbial abundance of sediments during N2O production were measured continuously on the south bank of the mangrove wetland in Jiulongjiang Estuary to study the impact of wastewater on the N2O emission and its mechanism in June 2017.The results showed that wastewater discharge immediately stimulated the sediment N2O emission,from<3 ?mol 11m-2 h-1 at the reference site without discharge to about 120 ?mol m-2 h-1.Although the flux significantly decreased in the 2nd day,the flux was also significantly higher at the discharged site than those at the reference site,and this stimulation lasted for about 10 days.Wastewater with a large amount of NH4+-N was discharged into mangrove sediments and NH4'-N content was up to 200 ?g g-1 in the sediment after discharge.The discharged sediment was collected in the 1st day had a significantly higher ammonia-oxidizing bacterial(AOB)amoA gene(encoding ammonia monooxygenase subunit A)abundance than that of ammonia-oxidizing archaeal(AOA-amoA),while the reference sediment had equal abundance of A OA-amoA and A OB-amoA genes.The wastewater discharge had no significant effect on the sediment narG and nirK genes(encoding nitrate reductase and nitrite reductase,respectively)and increased the nosZ gene(encoding nitrous oxide reductase).The similar temporal variation patterns betwe en N2O flux and sediment NH4+-N content or AOB-amoA gene abundance suggested that microbial nitrification plays an important role in the formation of N2O in sediments.(2)The pollution status and spatial distribution of antibiotics in mangrove sediments on the south bank of the Jiulongjiang Estuary were investigated and seventeen aquaculture antibiotics were selected.The results showed that Sulfanilamide(SA)and Chloramphenicol(CAP)were not detected at all sampling points.Ofloxacin(OFL),Florfenicol(FF)and Terramycin(TA)were detected at all sampling points.Sulfadiazine(SD),Sulfathiazole(STZ),Sulfapyridine(SPD),Sulfamerazine(SMR),Sulfameter(SME),Sulfamethizole(SMTZ),Sulfamethazine(SMT),Sulfamethoxazole(SMT),Sulfamethoxazloe(SMX),Sulfamonomethoxine(SMM),Sulfadimethoxine(SDP),Enrofloxacin(ENR)and Erythromycin(ERY)were detected at the different points.Antibiotics decreased with the depth of sediments and the antibiotic concentrations in 30-40 cm sediments were much lower than those in 0-10 cm sediments.Antibiotic were mainly concentrated in the surface layer.Compared with other estuaries and coastal regions in China,the extent of antibiotic contamination of Jiulongjiang Estuary mangrove wetlands cannot be ignored.(3)Short-term effect of antibiotics on the N2O emission in mangrove sediments under the action of nitrogen nutrient was done through laboratory simulation experiments.N2O emissions were stimulated by wastewater rich in NH4'-N added to mangrove sediments.At 0 h after the sewage was exhausted,under the effect of Ofloxacin,Florfenicol and Sulfamethazine with different concentrations(100 mg L-'(Florfenicol,Sulfamethazine),15 mg L-1,10 mg L-1,5 mg L-1,500 ?g L-1,50Og L-1),N2O flux in the sediment was lower than that in the control(without antibiotics)and significantly inhibited at different antibiotic concentrations.The results also showed that N2O flux of the treatment group showed an increasing trend with time on each sampling day.It indicates that the microorganisms have adapted to the inhibition of antibiotics.The level of flux recovery under the effect of high concentration antibiotics is lower than that of low concentration antibiotics.(4)Cumulative effect of antibiotics on the N2O emission and functional microorganisms in mangrove sediments under the action of nutrient and its mechanism were done through laboratory simulation experiments.Three typical aquaculture antibiotics(Florfenicol,Sulfamethazine and Ofloxacin)were selected and each concentration of antibiotics was set at three concentrations(10 mg L-1,500 pug L-1 and 5 ?g L-1).At the beginning of the experiment,N2O flux of the sediment under different concentrations of different antibiotics was significantly inhibited after the sewage was exhausted.Except for 10 mg L-1 Florfenicol,the sediment N2O flux returned to normal levels with the extension of sampling time and incubation time under the effect of other concentrations and antibiotics.The copy number of AOA-amoA gene in the sediment was higher than that of the reference group without antibiotics,and the key enzyme genes of denitrifying bacteria narG,nirK and nosZ were lower than the value of the reference group under the effect of three antibiotics which indicated that recovery of N2O flux in sediments may be mainly attributed to the recovery of nitrifying bacteria under the effect of antibiotics. |
PDF Full Text Request