Photodegradation Of DOM From Different Plant Sources In Eutrophic Lakes And Its Influencing Factors

Tai Lack is a typical eutrophic lake in China.In recent years,the algal bloom broke out and the pollution load of nutrients such as N and P increased greatly.It is a key problem to understand the photochemical degradation characteristics of DOM with the response of lake pollution.We used UV-vis,EEM fluorescence,NMR and FTIR to study the differences and the main influence of environmental factors on the degradation characteristics of DOM.Discussed internal cycling mechanism of DOM in eutrophication lakes from multiple perspectives.(1)The composition,structure and photodegradation characteristics of DOM from different plant sources are quite different.The proportion of protein substance of Chlorella was higher than Malayan and Hydrilla verticillata,and the humus content of Malayan and Hydrilla verticillata was higher than that of Chlorella.(2)After photodegradation,the relative molecular weight and the aromatic compounds were degraded of Malaya、Chlorella and Hydrilla verticillata.The relative molecular weight and aromatic compounds of Hydrilla verticillata DOM were more difficult change in photodegradation than the other two plants.Proteins in DOM were easily degraded,and some of them were degrade fulvic acids with strong aromaticity,which existed in water for a long time.(3)The DOM from Chlorella and Hydrilla verticillata in photodegradation responsed differently,under different DOC concentrations.Chlorella and Hydrilla verticillata are more likely to degrade to polymer DOM in low concentration,Chlorella is more likely to produce more aromatic and stable DOM in high concentration,while Hydrilla verticillata DOM are easy to release a large number of DOM,produce more aromatic and humus substances in low concentration.(4)The results of PARAFAC model analysis showed that Chlorella DOM recognized three fluorescence components:tryptophan C1,humus C2 and tyrosine C3;DOM from Hydrilla verticillata recognized three fluorescence groups,tryptophan C1 and humus C2;Tryptophan C1,humic acid like C2 and UVC like humus C3,were identified from Malayan DOM.The C2 component of DOM from Chlorella and Hydrilla verticillata is difficult to be degraded and into the water body,become the main source of the mixture of C+A peak of ecosystem for Taihu Lake.(5)Under different pH value influences,The absorbance coefficient of DOM from Malayan increased with the increase of pH value,and the total fluorescence intensity and the humic acid C2 fluorescence intensity also decreased with the increase of pH value;Under 7.0 and 9.0 condition,the DOM relative content accumulation is the highest,and the EEMs fluorescence spectra of DOM show the transformation of characteristic peaks;High pH value could promote the photodegradation of DOM in Malayan.Based on the above results found that environmental factors(pH value,DOC concentration)have an important impact on the chemical composition and spectral structure of DOM degradation products from plant sources.Therefore,in order to ensure the comparability of the results,should monitor and report the pH value and DOC concentration of the media.The protein substances and humus substances produced by degradation of plants release to the water body,promote the organic repollution,and provide sufficient material basis for the erupt of algae.The research results are helpful to explain the environmental trend of DOM in eutrophication lake,and provide theoretical basis and basic data for water quality assessment and pollution control of eutrophication lake.