Comparison of methods for indirectly estimating the phytoplankton population size structure and their preliminary modifications adapted to the specific conditions of the Baltic Sea
Justyna Meler, Sławomir B. Woźniak, Joanna Stoń‐Egiert
Abstract
A number of methods for indirectly estimating the size structure of the phytoplankton population in the Baltic Sea were analysed. These analyses were based on ~1000 samples of phytoplankton pigment concentrations and light absorption coefficients taken from surface waters, mainly in the southern Baltic Sea. Standard reference methods of diagnostic pigment analysis (DPA), originally developed for open ocean conditions, were employed to determine the proportions of pico-, nano- and microplankton groups in the population. A new preliminary modification of DPA, better adapted to the specific nature of the phytoplankton population in the Baltic Sea, is also proposed. Specific relationships between diagnostic pigments and chlorophyll a concentration are taken into account. The accuracies of different methods potentially useful in remote sensing observations of the Baltic Sea were examined. Several standard methods based on the total abundance of phytoplankton known from the literature were compared with the two new proposed variants. One with the newly developed typical Baltic pattern of change, representing the average relationship between the chlorophyll a concentration and the percentage contributions of the various size groups, and the other based on spectral absorption properties. The comparison indicated that if the standard methods known from the literature were applied to Baltic data, the estimates would be encumbered with significant errors, both systematic (up to ±30%) and statistical (up to 24%). It was also shown that the systematic errors of such estimates could be substantially reduced by applying one of the two preliminary variants of the methods proposed here.