Oceanologia (Apr 2022)
Validation of measurements of pine pollen grain concentrations in Baltic Sea waters
Abstract
Each spring, pine pollen coats considerable expanses of Baltic Sea surface waters. Measurements have shown that there are areas where its concentrations in this surface layer are so high that they are the dominant constituent of the suspended particulate matter (SPM) (Pawlik and Ficek, 2016). It then determines to a large extent the optical properties of the water surface, inter alia by modifying the sea colour. To date, however, the concentration of this constituent in the marine environment has rarely been studied, and its presence is not accounted for in the satellite algorithms used to define the composition and properties of sea water. This may well be the source of substantial errors in the remote sensing of the optical properties of the water and the measurement of concentrations of the optically important constituents it contains (chlorophyll a, TSM, CDOM). Measuring the concentration of pollen suspensions in Baltic Sea water, which often contains prodigious amounts of other SPM, is a daunting experimental challenge. Firstly, we characterized the pollen from pine trees growing near the southern shores of the Baltic Sea (northern Poland) using a microscope and two instruments routinely used in oceanography for measuring SPM size distributions: the LISST-100X and the Coulter counter. The measurements and analyses showed that a correct interpretation of the LISST-100X and Coulter measurements, is sufficient to count the number of pollen grains in distilled water alone. Furthermore, our laboratory analysis of the particle size distribution spectra enabled the fraction due only to pine pollen grains to be separated from the overall SPM. We then tested our method of analysing the SPM composition, which showed that the LISST-100x instrument is both a useful and an effective means for the in situ detection of the pine pollen that one sees in spring in Baltic waters.
