Geoscience Reference
In-Depth Information
Results of ionic strength on DOM photochemistry remain unclear. Experiments have
not shown evidence supporting the possibility that increasing salinity enhances the photo-
degradation of humic DOM (Minor et al.,
2006
) and anthropogenic DOM (Kong and Ferry,
2003
), yet studies do show an enhancement of DOM absorption photobleaching (Osburn
et al.,
2009a
; Grebel et al.,
2009
), though the latter study did not find an effect on DOM
fluorescence either in FA or in an algogenic DOM preparations. A multiestuary estuarine
mixing study coupled with photobleaching showed an increase in T and B peak fluores-
cence indicating possible proteinaceous material photoproduction (Boyd et al.,
2010b
).
Similarly, a burgeoning literature on DOM fluorescence in aerosols is describing the
abundance of atmospheric DOM with chemical properties similar to humic substances.
The atmosphere also contains substantial amounts of metals in dust and photochemistry
is important. Understanding the sources and reactivities of atmospheric DOM via fluores-
cence is important because of the many metal-ligand reactions that likely occur, some of
which is clearly related to DOM photochemistry in the atmosphere.
In terms of environmental effects on DOM fluorescence, it appears that the most dra-
matic and permanent effect would result from photochemistry or from dehydration caused
by evaporation. Largely, this is because pH, metal, and ionic strength effects appear to be
reversible, whereas the effects of dehydration and photochemistry are not. Thus, DOM
fluorescence ought to be most sensitive to global change conditions that promote photo-
chemistry (pH and metals are linked to this) or dehydration.
Linkages between DOM in soils, sediments, surface waters and the atmosphere are
clearly in need of further study because these systems are responsive to changing climate.
Taking a system approach to understanding the role of pH, salinity, and metals in terms of
DOM fluorescence will be particularly important now that multivariate statistical model-
ing (e.g., PARAFAC and other methods) can be used to determine similar fluorophore (or
fluorescing components) among these linked environments. The effects of soil salinization
on DOM properties using fluorescence has been investigated (Cilenti et al.,
2005
) and
dehydration effects of a drier climate clearly alter the fluorescence and perhaps quantity of
DOM in natural waters (Hudson et al.,
2009
). This understanding of extractable and pore
water DOM fluorescence properties in relation to pH and salinity changes - perhaps even
to temperature changes - affords the opportunity to examine these recorders of environ-
mental change for information regarding the global C cycle. The utility of fluorescence
for understanding the transport and cycling of DOM between the terrestrial, aquatic, and
atmospheric environments has been demonstrated, and we suggest the future discovery will
be utilizing DOM fluorescence further to link the chemistries of each environment with the
larger picture of environmental change.
Acknowledgments
Braden Giordano is thanked for help in preparation of this manuscript. Jasmine Saros
kindly provided conductivity data for Alkaline Lake. The Office of Naval Research (Work
Unit Nos. N0001401WX20072 and N0001403WX20946) supported field collection and
