Download D5.1: In-situ data quality control - AQUA

D5.1: IS data quality control
30/11/2014
HPLC
High Performance Liquid Chromatography (HPLC) enables chemical separation (i.e. based on
molecular polarity) and quantification of the pigments individually (i.e. even degradation products
can be determined), allowing therefore a more accurate measurement. An accuracy for Chl in the
order of <5% can be achieved with HPLC (Hooker et al., 2012). There is no unique HPLC method and
several protocols have been developed by different authors depending on the number of pigments
of interest and presence of different phytoplankton communities. In this project HPLC data from
FCUL is analyzed following the method of Zapata et al. (2000).
3.1.4 Quality control
It is strongly recommended to participate in intercomparison studies that are arranged among
partners like in the satellite validation teams (Sørensen et al., 2007a) or in national or international
laboratory performance studies for pigment analysis e.g. arranged by Quasimeme
(www.quasimeme.org). Even if a set of few laboratories can achieve high accuracy (< 5%) normally a
lower accuracy (< 20%) are common when many laboratories (> 15) with different methods are
involved (Sørensen et al., 2007a).
3.2
Phytoplankton absorption
3.2.1 Purpose of parameter(s)
The pigment absorption (APIG) and the bleached particle absorption (BPA) (using the MERIS
acronyms) are determined to be used in the algorithm developments and to verify the satellite
apig/Chl-a-ratios as well as contribute to the calculations of the non-pigment absorption
(BPA+CDOM).
3.2.2 Measurement principle and measurement challenges
After filtration of the water samples on a glassfiber filter the absorption coefficients for the
unbleached and bleached filters are determined with an integrating sphere and calculated as
described by Tassan and Ferrari (1995). To convert the result into the absorption of particles in a
suspension a divisor of 2 (the so-called β factor (Doerffer, 2002) is applied. Pigment absorption apig is
calculated as the difference between the absorption spectra of the unbleached and bleached filters,
adjusting the whole spectrum of apig so that it becomes zero at 750nm. Bleached particles
absorption at 442 nm, abp(442), is determined directly from the absorption spectrum of the
bleached filter. This value is again added to ay(442), and this sum is defined as the yellow substance
(YSBPA) in the MERIS protocol (Doerffer, 2002). The spectral shape of the bleached particle
absorption is supposed to follow an exponential function (Montagner, 2001). Sørensen et al. (2007b)
describe the methods used for NIVAs satellite products validation and the findings of the bio-optical
relations for Skagerrak area.
3.2.3 Protocol(s)
The protocol being used by both NIVA and FCUL is the one described in Tassan and Ferrari 1995,
2002. Shortly summarized the water samples should be filtered through 25 mm glass fibre filters
(GF/F) from Whatman Inc. (0.7 μm retention efficiency). The diameter of the particulate material
should be fitted to the actual integrating sphere used. Example for a 20 mm sphere (Labsphere
model RSA-PE-20) a diameter of the particles retained on the filter is 15 mm. The transmission and
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