Characterization Of Dissolved Organic Matter (DOM) In The Yangtze Estuary And Its Interactions With As/Sb

The spatial characteristics of Dissolved organic matter (DOM) in sediment pore waters，mainstream water and different sediment partical size of the Yangtze estuary were systematicallyconducted. DOM in pore water of Yangtze estuary was very variable which mainly composed oflow aromaticity and molecular weight materials. Three humic-like substances and oneprotein-like substance were identiifed by PARAFAC model. DOM abundance, aromaticity andmolecular weight in four regions following the order: Southern nearshore〉Northern nearshore〉River channel> Coastal areas, primarily influenced by human activities and tributaries inflow.The DOM quality indices in core of different depth were relative constant and increasedgradually with depth. DOM in core was mainly composed of humic-like material, which was dueto higher release of the sedimentary organic material into the porewater during early diagenesis.DOM molecular weight and aromaticity in mainstream increased from the upstream to thedownstream part of the estuary. Higher DOM abundance, degree of humiifcation and molecularweight were found in the pore water than in the surface and bottom water. Two humic-likecomponents (CI and C3) and one trypotphan-like component (C2) were identiifed by PARAFACmodel. The CI and C3were very similar and had a direct relationship with A355and DOC.DOM in pore water was mainly inlfuenced by CI and C3and increased along the river to thecoastal area. It was signiifcantly derived from sediment remineralization and depositing ofinflow from Yangtze River. DOM abundance in surface and bottom water decreased downstream.It was dominated by C2especially in the inflow of multiple tributaries affected by intensiveanthropogenic activity. Microbial degradation of exogenous wastes from tributaries input,shoreside discharge and shipping were dominant sources for DOM in surface and bottom water.The distribution of DOM extacted from different sediment size fractions of Yangtze estuarywas analysed.<25um possess the highest portion of the whole sediment. The aromaticity, acidicfunctional groups and fluorescence intensities of the DOM increased with decreasing sediment grain size. The molecular weight was ranged from2353to2556Da in different regions. Highermedian particle diameter, DOM lfuorescence and molecular weight, lower aromaticity of DOMcan be found in river channel than other regions primarily due to the pollutants input andintensive microbial activities in this area. Owing to the locating of mud area，sediment in coastalarea was mainly composed of small particals，leading to lower fluorescence of DOM. Thecharacteristics of DOM in different sediment size of northern and southern nearshore weresimilar. Higher acidic functional groups and greater aromaticity could be found in these tworegions. Compared to wet season，the aromaticity? functional groups and TOC contents of DOMincreased in dry season, while median particle diameter，DOM molecular weight andfluorescence decreased in dry season.The interactions between trivalent or pentavalent As/Sb and dissolved organic matter (DOM)in four regions and different partical size of the Yangtze Estuary were studied. Thetryptophan-like substance was the dominant component and played an important role in thecomplexation between DOM and As/Sb. The binding capacity of trivalent As/Sb with DOM washigher than that of pentavalent As/Sb with DOM. The higher binding capacity of Sb (III) withDOM was mainly due to hydroxyl and carboxyl groups. DOM from the north nearshore and<25um sediment partical size with the most acidic functional groups and greatest aromaticitypossessed the highest binding capacity. The increase in the UV absorbance and chargeneutralization further indicated the interaction between As/Sb and DOM. The complaxtion wasinfluenced by many factors. DOM fluorescence intensities increased with pH. A decrease influorescence intensity was found after the addition of NaCl to the As/Sb-DOM solution. Theresults also show that the addition of Ca(II) solution enhanced the lfuorescence intensity forAs/Sb-DOM lfuorescence, while slightly effect was observed after the addition of Mg(II).