The dependence of the fluorescence spectrum of phytoplankton on external influences

The concentration of phytoplankton is often used to assess the ecological status of water bodies; it is determined by the fluorescence intensity of chlorophyll-a, which is located in microalgae cells. Investigators do not usually take into account the effect of the medium on the fluorescence intensity when determining the concentration of phytoplankton. This article describes the use of a fibre-optic spectrometer developed by the authors to identify the relationship between the fluorescence of the chlorophyll-a in phytoplankton cells and under environmental conditions, such as temperature and illumination. A mathematical model is used to calculate the chlorophyll-a concentration based on fluorescence measurements and takes the temperature and amount of light into account. Using the resulting proportionality coefficient can reduce the error in the chlorophyll-a concentration determined using fluorescence methods by a factor of two. In this article the, authors describe the results of applying the method they developed to performance monitoring in the waters of the Gulf of Peter the Great in September and October 2013.