Geoscience Reference
In-Depth Information
fluorescence measurements. If possible samples should be analyzed immediately or within
24 hours and stored refrigerated (5°C) in the dark in the interim. The optical properties of
DOM samples change over time, in particular fluorescence intensities and after 7 days of
refrigerated storage the optical properties no longer reflect the natural signal from the lim-
ited data available. The hold time, though, is clearly dependent on DOM type and specific
hold time should be determined for each study relevant to the range of DOM under exam-
ination. If samples have to be preserved for longer periods of time, freezing and poisoning
represent options but as with refrigeration they should be tested as to their suitability for
the range of DOM under investigation. Acidification is not recommended as a preservation
method. Within natural pH levels found in the majority of aquatic systems the response of
CDOM absorbance and fluorescence measurements has been shown to be limited. There
is a general paucity of data on poisons such as HgCl
2
and NaN
3
and whether they may be
appropriate as preservatives for utilizing with the optical investigation of certain DOM
types. Similarly, the possibility of utilizing silver filters with antibacterial properties and
the difference in DOM optical results due to variation in filter pore sizes used needs further
research. Systematic studies utilizing a broad range of DOM samples undergoing a range
of storage protocols would provide highly useful data, particularly if the original DOM
samples were well characterized and thus observed changes could be related back to the
original composition/sample matrix, allowing informed choices on sample storage proto-
cols to be made for specific DOM sample types.
Acknowledgments
We thank Gareth Old, Dan Lapworth, Kenna Butler, and George Aiken for sharing data
with us and everyone who attended the AGU Chapman Conference on Organic Matter
Fluorescence in Birmingham, U.K. in 2008 for fruitful discussion. We also thank four
anonymous reviewers whose comments and suggestions improved this chapter. R.G.M.S
acknowledges support from NSF grants DEB-1145932, OPP-1107774 and ANT-1203885.
Finally, we thank the publishers who gave permission for figures and tables to be used.
References
Ahad, J.M.E., Ganeshram, R.S., Spencer, R.G.M., Uher, G., Gulliver, P., and Bryant, C.L.
(2006). Evidence for anthropogenic 14C-enrichment in estuarine waters adjacent to
the North Sea.
Geophys. Res. Lett
.,
33
, L08608, doi:10.1029/2006GL025991.
Andersen, D.O., Alberts, J.J., and Takacs, M. (2000). Nature of natural organic matter
(NOM). in acidified and limed surface waters.
Water Res
.,
34
(1), 266-278.
Astoreca, R., Rousseau, V., and Lancelot, C. (2009). Coloured dissolved organic matter
(CDOM). in Southern North Sea waters: Optical characterization and possible origin.
Estuar., Coast. Shelf Sci
.,
85
, 633-640.
Aufdenkampe, A.K., Mayorga, E., Hedges, J.I., Llerena, C., Quay, P.D., Gudeman, J.,
Krusche, A.V., and Richey, J.E. (2007). Organic matter in the Peruvian headwaters of
the Amazon: Compositional evolution from the Andes to the lowland Amazon main-
stem.
Org. Geochem
.,
38
, 337-364.
