Geoscience Reference
In-Depth Information
2
Fluorescence and Dissolved Organic Matter:
A Chemist's Perspective
George Aiken
2.1 Introduction
The importance of dissolved organic matter (DOM) in aquatic systems has been clearly rec-
ognized during the past 30 years. The compounds that comprise DOM in aqueous systems
often control ecological processes by influencing pH, serving as substrates for microbially
mediated reactions (Tranvik,
1998
; Findlay,
2003
), controlling the depth of the photic zone
(Wetzel,
2001
), and influencing the availability of nutrients (Qualls and Richardson,
2003
).
DOM also exerts strong chemical controls on geochemical (Hoch et al.,
2000
; Waples et al.,
2005
) and photochemical (Moran and Covert,
2003
; Stubbins et al.,
2008
) reactions, and
interacts strongly with trace metals (Perdue,
1998
; Haitzer et al.,
2002
) and organic pollut-
ants (Chin,
2003
), enhancing their apparent solubility and transport. In addition, DOM is a
constituent of concern in drinking water supplies through the formation of disinfection by-
products during the treatment process (Singer,
1994
; Kraus et al.,
2008
), and is an important
class of compounds comprising wastewaters (Baker,
2001
; Westerhoff et al.,
2001
).
The study of the nature and environmental significance of organic matter in natural
waters is hindered by its inherent chemical complexity, which poses a number of analytical
problems (Aiken and Leenheer,
1993
). A continuing need, therefore, is the development
of analytical approaches that provide relevant data defining both its composition and, thus,
reactivity. DOM optical properties, such as ultraviolet (UV)-visible spectroscopy, the spec-
tral slope parameter, specific UV absorbance (SUVA
254
), and fluorescence spectroscopy,
have been shown to be useful in a number of disciplines in the water sciences for studying
and monitoring both the concentration and nature of DOM in aquatic systems (Weishaar
et al.,
2003
; Helms et al.,
2008
; Spencer et al.,
2009
). Utilizing optical data is an attractive
approach for studying DOM because data collection is easy and straightforward, the data
provide information about both the concentration and composition of DOM (Weishaar
et al.,
2003
; Spencer et al.,
2009
), and detector systems can be employed for a variety of
process-based studies and separation techniques to study DOM composition. In addition,
optical data can be obtained
in situ
, allowing for the collection of high-frequency environ-
mental data in real time that can be used to understand better the source influences and
processing occurring within the system on the chemistry and export of DOM (Downing
et al.,
2009
; Saraceno et al.,
2009
).
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