Ref. No. [UMCES]CBL 2013-015
ACT VS12-02
emission intensities across each analytical batch (Coble et al. 1993). Finally, all sample EEM’s
were corrected for Raman and Rayleigh scattering peaks, following Zepp et al. 2004.
Excitation and emission windows for each instrument (based on the reported FWHM for
the filter sets as provided by manufacturers) were mapped onto each reference sample EEM
space and corresponding integrated quinine sulfate normalized fluorescence intensities obtained
for direct comparison to instrument output under the various challenge concentrations.
Colored Dissolved Organic Matter (CDOM)
Approximately 50 ml of the CDOM designated subsample were filtered using 47 mm
GF/F filters with low vacuum pressure and poured into an acid-cleaned, combusted, 60 ml amber
glass bottle. All samples were stored in the dark at 4° C until analysis, within approximately one
month of collection. A dual-beam spectrophotometer was blanked with MilliQ water in cuvettes
in both the sample and reference positions. Matched 10 cm quartz or optical glass cells were
used for a dual-beam spectrophotometer. MilliQ samples were run intermittently during each
analytical batch to assess instrument baseline drift. Scans were run between 200 and 800 nm and
electronic files were saved for each sample.
MilliQ blank and turbidity (750 nm) corrected spectra were used to estimate CDOM
abundance by non-linear regression of the absorption spectra over 400 – 575 nm.
a[
λ
] = a[400]e
(-
Sλ)
(1)
Where
a[
]
is absorption (m
-1
) at wavelength
,
a[
]
is absorption (m
-1
) at the anchor
wavelength of 400 nm, and
S
is the spectral slope (nm
-1
). Note that wavelength must be
expressed as
–
400
before fitting for the anchor value to be at 400 nm
. A[400]
is used as a
proxy for CDOM abundance in reference samples.
Chlorophyll a
Chlorophyll grab samples were analyzed on a Turner Designs 10AU fluorometer from
samples filtered on 2.5 cm GF/F filters and frozen at -20
o
C until analyzed according to Parsons,
et al. 1984. Optimum filtration volumes were determined on site. All chlorophyll analyses were
performed by the Chesapeake Biological Laboratory according to their existing SOPs. The
laboratory is a State of Maryland certified lab and has undergone previous audits by ACT during
prior evaluations. Samples were shipped to CBL in liquid nitrogen dry shippers to ensure they
remained frozen at the required temperature.
Turbidity
Turbidity concentrations of reference grab samples were determined by a Hach 1100AN
benchtop turbidity sensor in NTU. The lab analyzer was calibrated with certified standards prior
to use and a QA check of the standards were run during each analytical batch. Samples were run
immediately upon collection. The same instrument was used at each test site.
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