Bulk Preparation Of Dissolved Organic Matter In Seawater And Molecular Composition Characteristics Of Dissolved Black Carbon-like

Dissolved organic matter(DOM)participates in the carbon cycle,and the ocean is an important reservoir of DOM.Dissolved black carbon(DBC)is a vital part of DOM in seawater.Understanding the structure and composition of DOM in seawater at the molecular level and analyzing the molecular characteristics of DBC are the frontiers and hot spots in the study of the functions of DOM Biogeochemistry.A large number of inorganic salts in seawater have been restricting the extraction and purification of DOM,which further hinders the modern instrumental analysis of DOM at the molecular level,the preparation of DOM from large volume seawater with high efficiency and low loss is the first step to obtain representative and high purity samples.Reverse osmosis coupled electrodialysis(RO/ED)was an important technique for extracting DOM.It could prepare DOM in large volume,but it had the defects of low carbon content and high salt content.In this thesis,an improved technique of extracting DOM from large volume seawater by RO/ED was presented,the original RO/ED device was improved,the desalting improved method of RO/ED sample extraction was designed,an automatic control box was added,and the control device ran automatically.Compared with the previous method,the ash content of the sample extracted by the improved method decreased from 77% to about 37%,and the enrichment efficiency of organic carbon was improved significantly.RO/ED-DOM of Aoshan Bay and South China Sea were characterized by electron microscopy,spectroscopy,mass spectrometry and nuclear magnetic resonance,the results showed that the applicability of the improved samples was enhanced,at the same time,it provided data support for the research of DOM molecular composition in seawater.Using the improved RO/ED and other large-volume extraction devices,15.38 g seawater DOM samples were prepared.According to the DOM enriched by different extraction technologies,ultra-high resolution mass spectrometry was carried out at the molecular level to screen and identify the dissolved black carbon-like and analyze the molecular composition characteristics of DBC.The origin and destination of DBC were studied by the data of Pearl River Estuary(PRE)DOM which was from ultra-high resolution mass spectrometry,the abundance and types of DBC in the PRE detected by mass spectrometry showed a decreasing trend of estuary,nearshore sea and open sea in turn,this could indicate that DBC had degraded;Several DOM from typical seawater environment extracted by PPL solid phase extraction were characterized,it was found that DBC had fewer compounds with high oxygen number and low oxygen number,more compounds with medium oxygen number and better mass spectral response;The molecular characteristics of DBC in different seawater environments and in the DOM of Aoshan Bay extracted by three different large volume extraction methods were compared,it was found that the distribution of DBC correlated with the intensity of human activity and was more readily obtainable from the acidic components of DOM extracted by the XAD resin method.