Throughout the freshwater continuum,Dissolved Organic Carbon(DOC)and the colored fraction,Chromophoric Dissolved Organic Material(CDOM),are continuously being added,removed,and transformed,resulting in changes in the chromophoricity and lability of or-ganic matter over time.We examined,experimentally,the effect of increasing irradiation-intensities on the combined photochemical and microbial degradation of CDOM and DOC.This was done by using a simulated mixed water column:aged water from a humic lake was exposed to four irradiation-intensities-representing winter,early and late spring,and sum-mer conditions(0.10,0.16,0.36,and 0.58 W/m2)-and compared with dark controls over 37 days.We found a linear relationship between CDOM degradation and irradiation-intensities up to 0.36 W/m2;the degradation rate saturated at higher intensities,both at specific wave-lengths and for broader intervals.After 37 days at high irradiation-intensity,CDOM absorp-tion of irradiation at 340 nm had been reduced by 41％;48％of DOC had been removed and DOC degradation continued to increase.Aromaticity(SUVA254)declined significantly over 37 days at the two lowest but not at the two highest UV-intensities;levels in unexposed control water remained constant.Direct observations of the humic lake showed that CDOM absorption of irradiation(340 nm)declined by 27％from winter to summer.A model based on hydrological CDOM input and CDOM degradation calculated from field measurements of UV-radiation and experimental CDOM degradation with UV-exposure from sunlight accu-rately predicted the annual course as observed in the lake.With no external CDOM input,92％of the CDOM could be degraded in a year.The results support the notion that com-bined photochemical and microbial CDOM degradation can be remarkably higher in lakes than previously thought and that humic lakes retain their color due to light absorption by ongoing CDOM input.

Theis Kragh;Kaj Sand-Jensen;Emil Kristensen;Ole Pedersen;Mikkel Madsen-?sterbye

Department of Biology,University of Southern Denmark,Syddanmark 5230,Denmark;Freshwater Biological Laboratory,Department of Biology,University of Copenhagen,Copenhagen 2100,Denmark

环境科学学报（英文版）

[1]Theis Kragh;Kaj Sand-Jensen;Emil Kristensen;Ole Pedersen;Mikkel Madsen-?sterbye-.Removal of chromophoric dissolved organic matter under combined photochemical and microbial degradation as a response to different irradiation intensities)[J].环境科学学报（英文版）,2022(08):76-86

chromophoric,Chromophoric,chromophoricity,lability,Aromaticity

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