Geoscience Reference
In-Depth Information
DOM
CDOM
FDOM
Figure 8.1. Schematic of the overlap between dissolved organic matter (DOM), colored dissolved
organic matter (CDOM), and fluorescent dissolved organic matter (FDOM).
analysis. In addition, it is well suited for
in situ
or remote sensing measurement platforms,
which can offer high spatial resolution measurements. The major pitfall of this approach
is that the actual compounds responsible for the signal in general remain unknown. The
absorption and fluorescence signals of DOM represent the sum of all optically active com-
pounds present combined with any intramolecular charge transfer interactions between
them (Del Vecchio and Blough,
2004
). This complicates the interpretation of fluorescence
spectra to some extent as the changes occurring in fluorescence intensity and spectra are
due not only to the presence or absence of a specific fluorophore but also to the occurrence
or absence of additional interactions, such as quenching or charge transfer (Del Vecchio
and Blough
2004
; Stedmon and Bro,
2008
; Boyle et al.,
2009
). Despite this, some progress
has been made in identifying likely fluorophores present in fluorescent dissolved organic
matter (FDOM) samples.
In this chapter we briefly discuss the potential of the microbial food web as a source
and sink for FDOM and examine how the fluorescence characteristics change as a result
of microbial processing. In addition, the combined effects of microbial and photochemi-
cal degradation on FDOM characteristics are summarized. The literature on the subject is
vastly expanding and it is not our aim to provide an exhaustive review but rather to high-
light specific studies as examples of how fluorescence spectroscopy is being applied to
studying the microbial turnover of DOM in natural aquatic environments.
8.2. Sources
8.2.1 Allochthonous versus autochthonous
Irrespective of which aquatic system is studied, the sources of FDOM can be classified into
two categories: allochthonous and autochthonous. Allochthonous FDOM is material that is
