| Chaohu Lake is one of the five largest freshwater lakes in China.It is located in the middle of Anhui Province.It is surrounded by Hefei City and Chaohu City.It is an important drinking water source.The water environment is relatively closed.The tail water discharge from urban sewage plants,urban non-point sources,agricultural non-point sources and livestock and poultry breeding wastewater have brought antibiotics,resistance genes and other pollution problems to the lake.Sulfonamides,tetracyclines and other antibiotics have been detected in the water body.Dissolved organic matter is a heterogeneous mixture composed of monosaccharides,proteins,and humus.It can interact with antibiotics through mechanisms such as hydrogen bonding,chelation,and hydrophilic-hydrophobic distribution,affecting their migration,transformation,and biological toxicity.The lakeside zone is a transitional buffer zone of aquatic and terrestrial ecosystems.With surface runoff and flooding,DOM in the soil is released into the water body,affecting the environmental behavior of other pollutants in the water body.Based on this,this paper selects different types of soil(intertidal zone,plant wetland,forest land,field)in the north shore of Chaohu Lake as the research object,and explores the physical and chemical indexes and DOM spectral characteristics of different types of soil and its long-term flooding release overlying water.Typical tetracycline antibiotic oxytetracycline(OTC)and typical sulfonamide antibiotic sulfamethazine(SMT)were selected as quenchers to explore the effect of antibiotics on the release of DOM from overlying water by long-term flooding of lakeside soil,in order to provide data basis and scientific basis for water pollution control of Chaohu Lake.The conclusions are as follows:(1)The average contents of N and P in the riparian zone of Chaohu Lake were 0.83mg/L and 0.15 mg/L,respectively,while the average contents of COD and DOC were 33.27mg/L and 11 mg/L,respectively.The results of three-dimensional fluorescence spectroscopy(3D-EEM)combined with parallel factor analysis(PARAFAC)showed that the fluorescent substances of DOM in four types of soil in the northern lakeside zone of Chaohu Lake were mainly fulvic acid-like,tryptophan-like and humic acid-like components,among which fulvic acid-like accounted for the highest proportion.The relative content of protein-like substances in DOM of plant wetland soil was more than that of other land types.Ultraviolet spectroscopy(UV-Vis)and 3D-EEM parameters indicate that the overall humification degree of the lakeside soil is well developed,and DOM is contributed by both endogenous and exogenous sources,mainly exogenous.Among them,plant wetlands have more small molecular weight substances and higher autochthonous sources.(2)During the long-term flooding process,the content of total nitrogen(TN)in the overlying water decreased uniformly,and the content of total phosphorus(TP)and COD decreased rapidly in the early stage of flooding and then continued to maintain a low concentration.The DOC content also decreased rapidly in the early stage of flooding,and then showed a slow upward trend,reaching a peak around the 45 th day,and remained basically stable.The combination of 3D-EEM and PARAFAC showed that there were two types of protein-like and humus-like DOM in the overlying water released by soil flooding in the riparian zone of Chaohu Lake,mainly fulvic acid-like components.With the increase of flooding time,the content of protein-like components remained basically unchanged,while the relative concentration of humus-like components continued to rise.UV-Vis and3D-EEM parameters showed that the humus index in the DOM of the overlying water released from the lakeside soil increased with the increase of flooding time.The plant wetland soil released more hydrophobic components of DOM in the overlying water,and the content of colored dissolved organic matter(CDOM)and fluorescent dissolved organic matter(FDOM)was higher.At the later stage of flooding,the DOM components of the overlying water released by the four types of soils were basically the same,mainly fulvic acid.(3)Sodium humate indicator humic-like components,L-tyrosine and L-tryptophan indicator protein components were used as fluorescent substances,OTC,SMT and OTC +SMT were used as quenchers.UV-Vis showed that the quenching effect of OTC and SMT on typical DOM was static quenching.Synchronous fluorescence spectroscopy(SFS)combined with two-dimensional correlation spectroscopy(2D-COS)showed that the three groups of systems preferentially quenched the protein-like components,and the fluorescence peak was red-shifted,indicating that the microenvironment around the fluorophore changed.According to 3D-EEM combined with PARAFAC,the three quenching systems are mainly composed of four fluorescent components(tyrosine-like,tryptophan-like,fulvic acid-like and humic acid-like).The quenching efficiency of the three groups of systems is tryptophan,tyrosine and fulvic acid,and the quenching efficiency of SMT on the three typical DOM fluorescent components is better than OTC.OTC has a weak fluorescence peak at the peak of fulvic acid and humic acid,and SMT has no obvious fluorescence peak.(4)The DOM of overlying water released from lakeside soil after long-term flooding was dominated by two fluorescence peaks of fulvic acid-like peak and humic acid-like peak,and the relative concentration of fulvic acid-like was high.SFS combined with 2D-COS showed that compared with high molecular weight humic acids,antibiotics preferentially quench the low molecular weight fulvic acids.The combination of 3D-EEM and PARAFAC showed that when the concentration gradient of the three systems quenched the DOM,the higher the concentration,the higher the quenching efficiency,but the lower the reduction rate.SMT has a quenching effect on the characteristic fluorescent components of OTC.The higher the concentration,the more significant the quenching effect,and the quenching efficiency of fulvic acid is higher than that of humic acid.Figure [30] Table [7] References [130]... |
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