Composition And Environmental Effects Of Dissolved Humic Substances In Taihu Lake

Dissolved organic matter(DOM)is ubiquitous in almost all aquatic ecosystems,which plays a significant biogeochemical role in aquatic ecological system,such as controlling the speciation and bioavailability of trace metals.The environmental effects of DOM link up with composition,structure,distribution and transformation in the aquatic ecosystem.Lakes are the important part of the aquatic ecosystem.In the eutrophic lakes,concurrent with the harmful algal blooms process,large quantities of DOM products enter into the ecosystem of lakes.This consequently result in changes of the character of DOM and provided a large amount of ligands for metal complexation.In addition,microbes play a significant role in the degradation of DOM and influence its environment behavior.Being a potential bio-available nutrient pool,DOM couples with soluble nutrients released from inner sources in lakes,which significantly contributes to the oneset,duration,and decline of algal blooms in lakes.Humic substances(HSs)account for 40%-80%of the total DOM,which make a great contribution to the complexation of metals and organic matter.In order to better understand the effects of DOM on biogeochemical processes,characterization of HSs from different aquatic environments,such as eutrophic ecosystems,is essential.In this thesis,the aquatic dissolved HSs(DHS)contents and binding properties during bloom and non-bloom periods in Taihu Lake were investigated by elemental analysis,nuclear magnetic resonance(NMR),thermogravimetric analysis(TGA),fluorescence spectroscopy and two-dimensional correlation spectroscopy Fourier transform infrared spectroscopy(2D-COS-FTIR).DHS were isolated by methods established by the International Humic Substances Society(IHSS).The following is a summary of the results from this study:1.The content of carbon and oxygen(around 37%-56%)were high both in humic acids(HAs)and fulvic acids(FAs).Three kinds of fluorescent peaks were observed in both the non-bloom and bloom DHS.Compared with FAs,higher nitrogen content(6.4%vs.3.0%)was observed in HAs.FAs were found to contain more aliphatic compounds while the HAs contained more aromatic groups.The DHS in bloom period contained more nitrogen-containing compounds(5.3%)than that in non-bloom period(4.2%).Compared with the non-bloom DHS,more fresh materials were found in the bloom DHS,as well as the higher content of carboxyl and phenolic groups(32.8%vs.29.3%).Algal bloom period provided more ligands for metal complexation.2.The bonding sequence of non-bloom FA to Cu(II)should be:amide I C=O>N-H deformation and C=N stretching of amide II>polysaccharide C-O>aromatic C-H in cellulose>COO antisymmetric stretching>C-O stretching of phenolic and deformation of OH>phenolic O-H>carboxyl C=O.The sequential order of B-FA binding to Cu(II)is carboxylate C=O>amide C=O>phenol C-O>amide II in proteins>polysaccharide C-O>aliphatic C-OH>phenolic O-H>aromatic C-H.2D-COS-FTIR spectra evidenced the carboxyl groups in bloom FA had the fastest response to Cu(II)binding.Also,polysaccharide in bloom FA was more susceptive to Cu(II)concentrations than that in non-bloom FA.Compared with bloom FA,the N-rich organic compounds in non-bloom FA exhibited faster binding sequence with Cu(II).A comprehensive scheme about the interaction process of FA-Cu(II)showed that both nitrogenous and oxygenic groups in FAs were active in binding to Cu(II).The extracellular polymer substances(EPS),originated from the cyanobacterial bloom secretion and excretion,contained a large amount of polysaccharide(30%)and changed the composition of FAs.The binding sequence of non-bloom FA and bloom FA changed subsequently.3.The Proteobacteria,Actinobacterzia and Bacteroidetes groups have a strong ability to utilize N-rich organic compounds,carbohydrate and different molecular weight compounds.And the relative abundance ofβ-Proteobacteria in the non-bloom period was four times higher than that in bloom period,vice versa.The abundance of Fluviicola(0.02%vs.6.4%)、SAR 11(1%vs.28.8%)、hgcI(6.7%vs.19.8%)changed from the non-bloom period to bloom period may account for the different composition and binding properities of non-bloom FA and bloom FA.