INTERPRETATION OF FLUOROMETRIC CHLOROPHYLL REGISTRATIONS WITH ALGAL PIGMENT ANALYSIS ALONG A FERRY TRANSECT IN THE SOUTHERN NORTH-SEA

In 1991 chlorophyll a was measured continuously by fluorometry on the ferry 'Norstar', between Zeebrugge and Hull. In order to assess the usefulness of this platform for monitoring of long-term changes in phytoplankton distribution in the southern North Sea, calibration cruises were carried out in January, April, June and August with RV 'Holland' to relate algal pigment fingerprints to the fluorescence record. Chlorophyll a concentrations, determined after HPLC separation, allowed a quantification of the continuous fluorescence signal. The relation between fluorescence and chlorophyll a content was found to be rather constant in June and August and allowed a prediction of the chlorophyll a concentration from fluorescence measurements with 21%. In January and April, however, this relation was different for separate hydrographic regions. In April, a major chlorophyll derivative, an allomer indicative of degradation of algal matter, was abundant near the Belgian coast. During the decay of the Phaeocystis bloom, this high concentration of allomerized chlorophyll a increased the 'background' fluorescence signal. In January, enhancement of fluorescence caused by light scattering on non-algal suspended matter could be observed most clearly near the English coast, where the algal concentration was low (0.5 mug.dm-3) while suspended (inorganic) matter concentration was high (30 mg.dm-3). By applying linear relations, calculated for every hydrographic region, prediction of the chlorphyll a concentration could be improved to an accuracy of 38%. An analysis of taxon-specific chlorophylls and carotenoids reveals that the distribution of individual pigments and of pigment ratios was indicative of taxonomic composition of the phytoplankton. Patterns in pigment concentrations along the section suggest the same phytoplankton abundance gradients and patchiness as revealed by the continuous fluorescence measurement. A succession in the phytoplankton population was apparent: from diatoms and traces of green algae in January, to a spring bloom of Phaeocystis in April close to the Belgian coast, to diatom dominance in June, to a mixed population of green algae, diatoms and Prymnesiophyceae (probably Coccolithophorids) in August, at the end of the vegetative season. The presence, even occasional abundance, of green algae (carrying chlorphyll b) in the southern North Sea has not been reported earlier. The allomerized chlorophyll a concentration was most abundant near the coastal ends of the section during all cruises. Apparently, the phytoplankton is an important source of detritus in the North Sea

Gradient elution reversed-phase high-performance liquid chromatography for fractionation of complex mixtures of organic micropollutants according to hydrophobicity using isocratic retention parameters.

Gradient elution RP-HPLC is used as a suitable method to infer the hydrophobicity values (log K(ow)) of components in complex samples. In this study, the slope (S) and the intercept (log k(w)) of the linear relationship between the logarithm of the retention factor (log k) and the percentage methanol of the eluent (φ) were first obtained by isocratic runs for a set of micropollutants with diverse structures, similar to the contaminants to which the method will be applied. Both S and log k(w) obtained from isocratic runs could be related to log K(ow). Retention times in gradient elution, estimated from these isocratic parameters as a function of log K(ow), were in very good agreement with experimental values and an almost linear relationship can be established between log K(ow) and the retention time. This makes gradient elution RP-HPLC a suitable method to fractionate complex mixtures according to hydrophobicity. Copyright (C) 1999 Elsevier Science B.V