Distribution Characteristics And Source Of Dissolved Organic Matter(DOM) In Surface Water Of Apparent Contamination

In order to reveal the distribution characteristics and sources of DOM in landscape watercourses in Suzhou,the relationship between DOM and water sensory pollution in landscape watercourses is understood.In this study,23 landscape watercourses in Gusu District of Suzhou were taken as the research objects.Samples were collected once a month from 2019 to December 2020.Using three-dimensional fluorescence spectroscopy,UV-Vis absorption spectroscopy,high performance liquid chromatography and conventional water quality indicators,the spectral characteristics and sources of DOM in landscape watercourses were analyzed,and the following results were obtained:(1)The water body of the landscape river in the ancient city of Suzhou is generally polluted by nitrogen and phosphorous.Four components of DOM in water were identified by PARAFAC model,including the self-derived tryptophan C1(235,290/349 nm),the terrestrial humus C2(250,315/403 nm),the protein-like substance C3(230,275/319 nm)and the UVA humus C4(240,350/459 nm).Each component has homology,and the fluorescence component has significant correlation with nitrogen nutrients and chlorophyll a,indicating that DOM is related to the migration and transformation of nitrogen nutrients and the the growth of algae.The content of proteinlike substances in the DOM of landscape water body was the largest,accounting for 66.36%～76.84%of the total fluorescence intensity,and the proportion of humus-like fluorescence intensity was 23.15%～34.74%.Among the four types of pollution landscape river water body,there was no significant difference in the contents of component C1 and C4,and a large difference in the contents of component C2 and C3.The content of C2 was the highest in the organic and the content of C3 was the highest in the inorganic.Fluorescence index FI and self-source index BIX in water of various apparent pollution types were all large,humic index HIX was less than 3.5,and humic degree was weak,which was mainly endogenous.The absorption coefficient a254 was the largest and the aromaticity was the strongest in the organic type.In all types of water,the absorption coefficient ratio E2/E3 was less than 3.5,E2/E4 was larger,the spectral slope ratio SR was greater than 1,the relative molecular weight of DOM was smaller,endogenous contribution is relatively large.(2)During the early flood season,the total fluorescence intensity of DOM in the river was relatively higher due to the influence of initial rainwater,but reduced signigicantly towards the middle and late flood season.Fluorescence characteristic parameters indicated that autochthonous contribution of DOM were obvious during the early stages of the flooding season.On the contrary,there was increased levels of DOM largely from terrestrial origin,during the middle flooding period.During the whole flood season,SUVA254,SUVA260 and E2/E3 show the same trend,that is,decreasing first and then increasing.As a result of the continuous heavy rainfall durng the flood season,the nitrogen and phosphorus nutrient content in the channel increased.The algae population did not proliferate in large quantities because of the strong hydrodynamic conditions experienced during the entire flooding season.The fluorescence components C2,C3 and C4 exhibit a significant correlation coefficient(P<0.01)with the characteristic parameters(FI,HIX,BIX,β/α).All fluorescence components had significant correlation(P<0.05)with DOC.There was a significant correlation between fluorescence component C1 and Chl a.Principal component analysis shows that DOM components in the landscape river during different periods of flooding season exhibit notable differences,and the continuous heavy rainfall during the flooding season has an obvious influence on the content of C2,C3 and C4 components in the water body.(3)The molecular weight of DOM in interstitial water and overburden water is about 1kDa,and the molecular weight tends to increase with the passage of time.The contents of proteinoids in interstitial water and overlying water were the highest,accounting for 68%～79%of DOM,while the contents of humus were low,accounting for 21%～32%of DOM,and they were dominated by low excitation tryptophan.From July to September,DOM content in interstitial water increased greatly,and DOM content in overlying water gradually increased,which may be due to the deposition of algae in the river bottom after summer algae burst,and then released into interstitial water and overlying water after cracking.The fluorescence index FI of interstitial water and overlying water showed a great difference in July,and then increased first and then decreased with the same trend,but both were greater than 1.2.The BIX index values are all greater than 0.8 and biased toward 1.The humification index HIX values were all less than 4,and the gap water and overlying water showed the same trend of decreasing.There is a close relationship between gap water and DOM in overlying water in Suzhou landscape watercourse,and gap water is the potential source of DOM in overlying water.