THE DETERMINATION OF ALGAL BIOMASS (AS CHLOROPHYLL) IN SUSPENDED MATTER FROM THE ELBE ESTUARY AND THE GERMAN BIGHT - A COMPARISON OF HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY, DELAYED FLUORESCENCE AND PROMPT FLUORESCENCE METHODS

HPLC methods are now widely accepted as being the only accurate means of quantifying chlorophyll in aquatic systems. Very little is known ab out the comparability of HPLC with conventional in situ prompt fluores cence methods and with newer techniques involving the measurement of d elayed fluorescence of phytoplankton (measure of living algal biomass) in aquatic systems. This paper investigates the use of HPLC for the c alibration of in situ delayed fluorometric and Turner fluorometric met hods and the correlation of these methods to one another when applied to chlorophyll measurements in waters from the Elbe estuary and the Ge rman Bight. The data shows that the correlations of HPLC to both metho ds were high r(2) = 0.7-0.99 when all the samples taken were from the reaches of the river Elbe (605-725 km). The correlations of all method s were low at r(2) = 0.45-0.52 for samples taken in the saline part of the Elbe plume and when the chlorophyll concentrations were low (0.2- 9 mu g.l(-1) ) and with comparatively high chlorophyllide and chloroph yll c contents. Generally the correlations of HPLC to delayed fluoresc ence were better than the other correlations. This was probably due to the fact that delayed fluorescence measurements are not affected by t he presence of other chlorophylls and their breakdown products whereas prompt fluorescence signals are. Delayed and prompt fluorescence meth ods can be calibrated accurately against HPLC values for chlorophyll i n the natural samples and correlations remained good over several days . However, we suggest that it is advisable to check these as often as possible, particularly in the face of measurable changes of turbidity, salinity or spectral properties of the water. In this work the May an d October slopes for the comparisons HPLC: delayed fluorescence in the limnic Elbe below Hamburg were similar (i.e. 223-245). A significantl y lower slope (160) was found for the 32 stations in the Elbe mouth/Ge rman Bight, This indicates that we were dealing with different water b odies and thus different algal populations and is backed up by the HPL C fingerprints of the samples. Our work shows conclusively that althou gh a correlation may be good between absolute chromatographic methods and fluorometric/photometric methods, one cannot extrapolate a long-te rm conversion factor which holds for different sampling times or sites in any one system, not to mention between systems. (C) 1998 Elsevier Science B.V.