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Photochemical degradation of chromophoric dissolved organic matter
PRIMARY RESEARCH PAPER
Photochemical degradation of chromophoric-dissolved
organic matter exposed to simulated UV-B and natural
solar radiation
Yunlin Zhang ? Mingliang Liu ? Boqiang Qin ?
Sheng Feng
Received: 25 August 2008 / Revised: 19 January 2009 / Accepted: 24 January 2009 / Published online: 13 February 2009
Springer Science+Business Media B.V. 2009
Abstract Photochemical degradation of chromo-
phoric-dissolved organic matter (CDOM) by UV-B
radiation decreases CDOM absorption in the UV
region and fluorescence intensity, and alters CDOM
composition. CDOM absorption, fluorescence, and
the spectral slope indicating the CDOM composition
were studied using 0.22-lm-filtered samples of
Meiliang Bay water from Lake Taihu that were
exposed to short-term (0–12 h) simulated UV-B
radiation and long-term (0–12 days) natural solar
radiation in summer. CDOM absorption coefficient
and fluorescence decreased with increasing exposure
time, which relates to the amounts of absorbed light
energy. The decreases of CDOM absorption and
normalized fluorescence corresponded to first order
kinetics reactions. Different decreases of CDOM
absorption and fluorescence at different wavelengths
suggested that the composition of CDOM changed
when it absorbed ultraviolet radiation. Photochemical
degradation increased the spectral slope during 275–
295 nm region (S275–295) but decreased the spectral
slope during 275–295 nm region (S350–400). The slope
ratio SR (S275–295:S350–400) increased in the photo-
chemical process, which could be used as an indicator
of photobleaching and composition change of
CDOM. Our results show that photochemical degra-
dation is important in the cycling of CDOM, which
indicated change in the composition of CDOM.
Keywords Absorption coefficient
Fluorescence Photobleaching Spectral slope
Introduction
Chromophoric-dissolved organic matter (CDOM) is a
colored fraction of DOM. Because its strongest
absorption is within the ultraviolet (UV) light wave-
lengths, CD
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