Isolation And Chemical Characterization Of Natural Organic Matter In Coastal Wetland And Coastal Seawater

Natural organic matter(NOM)in coastal environments is an important component of the global carbon cycle and plays an important role in the response to climate change.The bioavailable fraction of NOM can be consumed by heterotrophic microbes,and is an important component of the marine microbial community.Coastal NOM also plays a key role in the chelation of metal and organic pollutants,influencing metal and organic toxicity and bioavailability.Due to the heterogeneity and complexity of the structural composition of marine NOM,and the limitations of the separation and extraction methods used,knowledge of its properties and geochemical behaviour remains elusive.This thesis focuses on the separation,purification and chemical characterization of NOM in coastal environments.Dissolved organic matter(DOM)and particulate organic matter(POM)were isolated from coastal seawater,and humic substances(HS)from coastal wetland soils.The organic matter samples obtained were analyzed using state-of-theart instruments.such as Ultra-high resolution mass spectrometry and nuclear magnetic-resonance(NMR)spectroscopy.The main findings and conclusions are as follows:1.Coastal wetlands are an important component of marine blue carbon,and research on the organic carbon composition of Yellow River Delta wetlands is helpful for the implementation of carbon sequestration and storage in Yellow River Delta wetlands.Soil/sediment physicochemical properties were analyzed and humic substances(HS)were extracted.The results showed that the soil/sediment grain sizes at the studied stations were mainly silt and sand.Due to the lack of vegetation and low soil organic carbon content on the surface of the wetlands,the humic substances(HS)fraction isolated in the soils/sediments is mainly fulvic acids(FA),while the humin(HM)and humic acids(HA)fractions were difficult to isolate due to their close association with minerals.When the FA and HA fractions were compared,we found that the O/C ratio of FA was higher(0.66-0.78),indicating a higher content of oxygen-rich functional groups such as COOX in FA.With increasing soil depth,the aromaticity of the soil FA samples gradually increased(29.5 to 30.3 to 31.4),and the surface(0-20 cm)FA had the highest HI(2.09)compared to the deep soil(20-40 cm and 40-60 cm)FA(1.75 and 1.79).2.In addition to the differences in apparent molecular weight(molecular size),highly diverse Marine DOM molecules also have differences in polar functional groups,and the different resins in tandem methods can be used to separate and enrich DOM subcomponents with different polarity.The DOC recovery of PPL-SPE,the most commonly used method to isolate DOM,is only 5060%.Using PPL→DAX-8→XAD-4 method to separate and enrich DOM subcomponent,and the obtained DOM fractions are mainly PPL-DOM and Amphiphilic Acid(AMPA).and this method increased the DOC recovery of Aoshan Bay and Shazi Bay seawater by 21.9%and 18.8%,respectively.The molecular formulas of the two AMPA samples which cannot be found in PPLDOM samples,were sifted and found to have higher relative intensity-weighted average molecular weight(415.5 and 436.6)and higher abundance of CHON compounds(72.4%and 50.0%),indicating that PPL seawater effluents contain a mass of nitrogen-containing compounds with higher molecular weight.And the optimized PPL→XAD-4 resins in tandem were applied to isolate large volumes of seawater from 400 m depth of Xisha and were found to increase the DOC recovery by 4.89-6.45%.3.Dissolved organic carbon changes under the influence of seawater season,algal growth.microbial metabolism,etc.,while the chemical composition and molecular level changes of DOM are still not well understood.Using PPL resin to isolate DOM of different seasonal coastal seawater in Aoshan Bay,Qingdao,and the results showed that C content,N content and C/N molar ratio are 46.7-52.1%,2.94-3.13%and 18.2-20.5,respectively.Solid-state 13C NMR results showed that PPL-DOM was mainly composed of aliphatic,carbohydrate,carboxyl,amide and aromatic compounds,and the Hydrophilicity Index(HI)of the four seasonal samples was sequenced as spring>autumn>summer>winter,and the aromaticity was sequenced as autumn>summer>spring ≈ winter.Orbitrap mass spectrometry(Orbitrap MS)showed that PPL-DOM is dominated by CHO compounds(with relative abundance over 70%)and CHON compounds(with relative abundance over 10%),and has over 100 different class species.The composition of the four seasonal DOM samples in Aoshan Bay was influenced by the seasons.4.DOM is an operational definition,DOM and POM are the molecular-size continuum.PPLDOM and POM were extracted from the mixed waters in the mesopelagic layer at F Station in the northern South China Sea,and infrared spectroscopy,solid-state NMR,solution-state NMR and high-resolution mass spectrometry were performed,and the results showed that aliphatic compound signals,carbohydrate signals and aromatic compounds were mainly used in POM and PPL-DOM samples,and there were obvious amino sugar signals and peptidoglycan signals.The structural similarities of some components in both samples may sugguest the correlation and transformation between DOM and POM.