Optical Dynamics,distribution And Sources Of Chromophoric Dissolved Organic Matter In Lake Fuxian

Chromophoric dissolved organic matter(CDOM)is coloured fraction of dissolved organic matter.CDOM's behavior of solar radiation absorbing affects the primary productivity of lake ecosystems.The research to exploring the spatio-temporal variation,compositions and sources of CDOM in Lake Fuxian can provide data and theoretical support for the lake's protection and management.The basin's investigation results of Lake Fuxian in 2017 and 2018 are as follows:In 2017,the average value of a(254)in Fuxian Lake was 3.47±0.57 m-1,ranging from 1.82 to 5.22 m-1.The average value of a(254)in spring,summer,autumn and winter was 3.20±0.47 m-1,3.76±0.64 m-1,3.67±0.50 m-1 and 3.23±0.38 m-1,respectively.The a(254)was higher in summer than in winter and spring significantly(P<0.01),and higher in autumn than in winter and spring significantly(P<0.01).As for spatial variation,in May,a(254)on north shore was higher than on south shore significantly(P<0.01),but there was no significant difference in February,August and November.The spatial distribution of CDOM may be affected by land use,rainfall,temperature and light radiation.According to the results of parallel factor analysis,four fluorescent components were identified:two tyrosine-like fluorophores,one tryptophan-like fluorophore and one humus-like fluorophore.CDOM showed strong microbial fluorescence characteristics with little humification characteristics.In a word,the CDOM abundance in Lake Fuxian was low,and the autochthonous CDOM was dominant DOM pool during the annual survey.With basin investigation of Lake Fuxian in dry and rainy seasons in 2018,the CDOM were divided into five components,including two tyrosine-like fluorophores,one tryptophan-like fluorophore and two humus-like fluorophores.In dry season,the average value of a(254)in river was 10.38±5.09 m-1,and the one in lake was 3.85±0.55 m-1.In rainy season,the average value of a(254)in river was 13.43±9.70 m-1,and the one in the lake was 4.28±0.24 m-1.As for a(254)in river,there was no difference between dry season and rainy season(P>0.05),while a(254)of the lake in rainy season was higher than in dry season significantly(P<0.05).In dry season,the average value of fluorescence intensity in rivers was 83.85±19.02 R.U.and the one in the lake was 109.17±30.08 R.U..In rainy season,the average value of fluorescence intensity in rivers was 25.54±11.57 R.U.and the one in the lakes was 13.18±7.23 R.U..The total fluorescence intensity of rivers and lakes in dry season is higher than that in rainy season.In dry season,rivers'CDOM mainly showed tyrosine-like fluorescence characteristics,while in rainy season,rivers' CDOM mainly showed humus-like fluorescence characteristics.The total fluorescence intensity of wet deposition in rainy season was 754.70 R.U.,and that of dry deposition was 247.48±37.65 R.U.,which mainly showed microbial fluorescence characteristics.The direct contribution of river and atmosphere input to CDOM pool of the lake were little because of the large amount of water storage and long water residence time which allowed sufficient action of dilution,photodegradation and biodegradation.