Research On The Rates And Kinetics Of The Denitrification And Anammox In Sediments Lake Taihu

Eutrophication of lakes is a global problem.Eutrophication can lead to a series environmental problems,such as harmful algae blooms,death of creatures,and deterioration of water body.It has been considered that eutrophication of Lakes is partially derived from excessive input of reactive nitrogen(Nr).Microbially mediated denitrification and anammox are the fundamental pathways to remove nitrogen in aqueous ecosystems.Therefore,the study of the two pathways can is theoretically and scientifically crucial to our understanding of the mechanism of the nitrogen cycle in lakes and the prevention and control of nitrogen pollution.The present study was supported by the State Key Program of National Natural Science of China(No.41230640).In the present study,Meiliang Bay,a mid-eutrophic region,and Xuhu Bay,a mesotrophic region,in Lake Taihu were chosen as typical areas.Based on the molecular techniques and the revised 15N isotope pairing technique(r-IPT),denitrification and anammox were studied using 15N slurry experiments and 15NO3-intact-core continuous-flow experiments.In details,we quantified the functional gene abundances of denitrifying and anammox bacteria,analyzed the difference between and the applicability of the two r-IPT,r-IPTra and r-IPTv,calculated the rates of denitrification and anammox and the contribution of anammox to nitrogen loss in sediments,and obtained the kinetics of denitrification and anammox.The main results are as follows.(1)The occurrence of denitrification and anammox in sediments of study areas was proved based on the quantitative PCR(qPCR)techniques.Gene abundance of denitrifying bacteria was measured as 3.97×109 and 5.17×109 copies g-1 dry sediments,and gene abundance of anammox bacteria was measured as 1.88×108 and 8.07×107 copies g-1 dry sediments,in Meiliang Bay and Xuhu Bay,respectively.The gene abundance of denitrifying bacteria is more than 10 times that of anammox bacteria.The production types of 29N2 and 30N2 in two treatments,100μM 15NH4++100 μM 14NO3-and 100μM 15NO3-in 15N isotope slurry experiments further suggested the occurrence of denitrification and anammox in both sites.(2)The r-IPTv was applicable to the calculation of the nitrogen loss rates in sediments of both Meiliang Bay and Xuhu Bay,while the r-IPTra.could only result in the correct rates in Xuhu Bay,where the contribution of anammox to nitrogen loss was relatively low.The denitrification rates,the anammox rates,the true N2 production rates,and the contribution of anammox to nitrogen loss were calculated using the r-IPTv,and were 3.09,1.47,4.5 μmol N m-2 h-1 and 32.2%in Meiliang bay and 0.69,0.02,0.71 μmol N m-2 h-1 and 2.8%in Xuhu Bay,respectively.These values increased with elevated nutrient levels.(3)The results from the continuous-flow experiments incubated with a series of 15NO3-concentrations suggested that the responses of denitrification and anammox to nitrate could be well described by the Michaelis-Menten model.The maximum rates(VM)of denitrification were 152.48 and 252.55 μmol N-2 h-1,and the half saturation rates were 796.15 and 684.37 μM in Meiliang Bay and Xuhu Bay,respectively.And the VM of anammox were 19.75 and 5.66 μmol N-2 h-1,and the KM were 153.70 and 423.88μM in Meiliang Bay and Xuhu Bay,respectively.