PIGMENTUM: an easy pigment-based tool for monitoring phytoplankton community composition

Abstract

Phytoplankton monitoring is essential for understanding the functioning of aquatic ecosystems and for assessing water quality. Based on pigment analysis, different mathematical tools have been developed to relate pigments and phytoplankton groups and determine the contribution of each of these groups to the total phytoplankton biomass. However, most of these tools have several drawbacks, such as the need for a minimum sample number or previous knowledge on community composition. The present study proposes a new chemotaxonomic tool, ‘PIGMENTUM’, based on simultaneous equations that take into account the lack of exclusiveness of diagnostic pigments and which defends the use of ‘pigment groups’ to define the community composition over ‘taxonomic groups’. Additionally, PIGMENTUM does not require prior knowledge on the community composition of the study area, generic pigment ratios are applied, samples are treated independently and it allows individualised ratio correction if necessary. The accuracy of PIGMENTUM was tested with a data series of 330 samples containing different trophic statuses (0.1-251 μg l-1 of chlorophyll a [chl a]) and water masses (salinities between 0 and 36 PSU). The median similarity between the calculated and the real chl a was 82%, and 98% of the samples obtained reliable results, with the tool being especially accurate for eutrophic and hypereutrophic waters. PIGMENTUM was thus proven efficient for phytoplankton monitoring in a wide variety of aquatic systems and environmental conditions, allowing monitoring the variability of the community over time and space and/or determining the groups causing eutrophication or isolated blooms, without the need for using additional techniques.