Geoscience Reference
In-Depth Information
in a given system. For example, although amino acid-like FDOM is pretty clearly associ-
ated with microbial processing of the DOM pool, the interpretation of amino acid-like
components in the FDOM pool is complicated by the fact that these fluorophores are both
produced and removed by microbial activity. Future work should be aimed at determining
differences between recently produced amino acid-like FDOM from microbial degrad-
ation of colorless DOM versus amino acid-like FDOM associated with humic material that
may represent an important bioavailable component of humic DOM.
One can hypothesize that the degree to which DOM has been exposed to sunlight and
microorganisms (e.g., its diagenetic state) is generally inversely related to the rate at which
it can be further degraded by photo and biochemical degradation. In other words, as the
substrates most labile to photo and biochemical degradation are preferentially removed,
the remaining DOM is degraded more slowly. One question is whether this hypothesis
is reflected in the FDOM signature, for example, whether the diagenetic state of DOM
is reflected either in the FDOM signature or perhaps from photo or bioassays based on
changes to FDOM during photo- and biochemical incubations.
Why is understanding this link important? The reason is that in several key environ-
ments, there is evidence for the current or predicted increase in DOM in surface waters.
Climate change-induced alteration in the hydrology of catchments are increasing the load-
ing of terrestrial organic material to surface waters, such as the observed increased DOC
concentrations in European and North American surface waters (Monteith et al.,
2007
) and
the expected increase in DOC concentrations from permafrost thawing in Arctic regions
(Rember and Trefry,
2004
, Frey and Smith,
2005
). The likely fate and impact of this addi-
tional DOM supply on aquatic ecosystems are unknown. The bioavailability of the organic
matter associated with this increased supply has great influence on the net result, as an
increased supply of labile carbon either directly or indirectly via photochemical process
will favor heterotrophic bacteria in competition with phytoplankton for mineral nutrients
(Thingstad et al., 2008). If we are able to link the FDOM signature of “new” DOM in a
given system to its susceptibility to photo and biochemical degradation, it would signifi-
cantly improve our ability follow and attempt to predict its fate and impact within the con-
text of the regional and global carbon cycling.
Acknowledgments
C.A. Stedmon was funded by the Danish Research Council Grant no. 272-07-0485 and
Carlsberg Foundation Grant no. 2007-01-0124. We also thank two anonymous reviewers
for their constructive comments on the text.
References
Aitkenhead-Peterson, J.A., McDOwell, W.H., and Neff, J.C. (2003). Sources, production
and regulation of allochthonous dissolved organic matter inputs to surface waters.
