Geoscience Reference
In-Depth Information
6
Experimental Design and QualityAssurance:
In Situ
Fluorescence Instrumentation
Robyn N. Conmy, Carlos E. Del Castillo, Bryan D. Downing,
and Robert F. Chen
6.1 Introduction
Both instrument design and capabilities of fluorescence spectroscopy have greatly advanced
over the last several decades. Advancements include solid-state excitation sources, integra-
tion of fiber optic technology, highly sensitive multichannel detectors, rapid-scan mono-
chromators, sensitive spectral correction techniques, and improved data manipulation
software (Christian et al.,
1981
; Lochmuller and Saavedra,
1986
; Cabaniss and Shuman,
1987
; Lakowicz,
2006
; Hudson et al.,
2007
). The cumulative effect of these improvements
have pushed the limits and expanded the application of fluorescence techniques to numer-
ous scientific research fields. One of the more powerful advancements is the ability to
obtain
in situ
fluorescence measurements of natural waters (Moore,
1994
).
The development of submersible fluorescence instruments has been made possible by
component miniaturization and power reduction including advances in light source tech-
nologies (light-emitting diodes, xenon lamps, ultraviolet [UV] lasers) and the compatible
integration of new optical instruments with various sampling platforms (Twardowski
et al.,
2005
and references therein). The development of robust field sensors skirts the
need for cumbersome and or time-consuming filtration techniques, the potential artifacts
associated with sample storage, and coarse sampling designs by increasing spatiotemporal
resolution (Chen,
1999
; Robinson and Glenn,
1999
). The ability to obtain rapid, high-
quality, highly sensitive measurements over steep gradients has revolutionized investiga-
tions of dissolved organic matter (DOM) optical properties, thereby enabling researchers
to address novel biogeochemical questions regarding colored or chromophoric DOM
(CDOM).
This chapter is dedicated to the origin, design, calibration, and use of
in situ
field fluor-
ometers. It will serve as a review of considerations to be accounted for during the operation
of fluorescence field sensors and call attention to areas of concern when making this type
of measurement. Attention is also given to ways in which in-water fluorescence measure-
ments have revolutionized biogeochemical studies of CDOM and how those measurements
can be used in conjunction with remotely sensed satellite data to understand better the bio-
geochemistry of DOM in aquatic environments.
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