Composition,Structure And Migration Behavior Of Dissolved And Particular Organic Matter In Baisha River

Organic matter(OM),which is a complex heterogeneous mixture,is widely present in various water environments.As an important carbon source of aquatic environments and a carrier of pollutants,OM not only affects the balance of aquatic ecosystems,but also plays a crucial role in the migration and transformation of nitrogen,phosphorus and other pollutants in water environments.Dissolved organic matter(DOM)and particular organic matter(POM)are two important components of OM,and their migration behavior in rivers has an important impact on river carbon cycling and aquatic ecology.It can provide basic data and theoretical support for river carbon cycling and migration of pollutants by studying the composition and spatial variation characteristics of DOM and POM in rivers.Baisha River in Gaozhou city was selected as the research object to analyze the composition and spatial evolution characteristics of dissolved organic matter(DOM)(<0.45 μm),particulate organic matter 1(POM1)(>0.7 μm),and particulate organic matter 2(POM2)(0.45-0.7 μm).Three-dimensional fluorescence spectroscopy combined with parallel factor analysis(PARAFAC)was used to reveal the composition characteristics of DOM,POM1,and POM2.Moreover,two-dimensional correlation spectroscopy(2D-COS)and perturbation-correlation moving-window two-dimensional correlation spectroscopy(PCMW2D-COS)combined with potential sources of OM were applied to analyze the source and trace the variations of DOM,POM1,and POM2 components along the baisha River.Fourier transform infrared spectroscopy combined with 2D-COS and PCMW2D-COS were used to identify the functional groups and characterize the structural spatial variation of DOM,POM1,and POM2.Redundancy analysis(RDA)and partial least squares structural equation model(PLS-SEM)were used to explore the potential connections between DOM,POM1,and POM2 and their response to the water quality.The main conclusions are as follows:(1)The components and the functional groups are different significantly between DOM,POM1 and POM2.Four fluorescent components,namely fulvic acid-like,humic acid-like,tryptophan-like,and tyrosine-like,were extracted from the 3D fluorescence spectra of DOM,POM1,and POM2.Moreover,fulvic-like and humiclike substances are the main components in DOM,whereas tyrosine-like substances dominate in POM1 and POM2.Carboxyl-OH,aromatic C-H or C=C,crystalline cellulose,phenolic aldehyde O-H,amide(Ⅰ)C=O,and aliphatic C-OH are present in DOM,POM1,and POM2.Aromatic N=O is unique to POM1 and POM2,while aliphatic C-OH is a specific functional group of DOM.(2)The main source of organic matter in Baisha River was centralized treatment facilities for rural domestic sewage and drainage from coastal fish ponds.The homology of substances such as fulvic acid and humic acid in DOM,POM1,and POM2 shows similarity in their variations along the river.Similarly,the sources of tryptophan-like and tyrosine-like are consistent,as evidenced by similar variations along the river.However,the variations of functional groups in DOM,POM1,and POM2 exhibit significant differences along the river.The phenolic O-H of DOM undergoes preferential changes and exhibits the greatest intensity changes.However,the aromatic N=O of POM1 and POM2 have the greatest variation along the river.Based on 2D-COS of organic matter components and functional group structures,organic matter components are more susceptible to the influence of the surrounding environment of the river than the functional groups.(3)The components of DOM are influenced by the water quality and POM.Water quality has a significant positive effect on DOM components.POM2 was a "bridge" between DOM and POM1,which also called an intermediate connection.POM2 not only degrades to generate DOM,but also aggregates to form POM1.Additionally,POM1 separates to form POM2,which further degrades to generate more DOM.Therefore,POM1 indirectly affects the content of DOM components.Thus,it is necessary to comprehensively consider both dissolved and particulate organic matter for studying organic matter of the river.