Spectral discrimination of phytoplankton colour groups: The effect of suspended particulate matter and sensor spectral resolution

Abstract

Remote sensing has been used extensively to provide quantitative information on the distribution of phytoplankton in inland waters through the surrogate mapping of chlorophyll a, but as chlorophyll a is common to almost all species of phytoplankton it cannot provide any information on the taxonomic composition of phytoplankton communities. However, the varied optical properties of phytoplankton taxa may present a means to their discrimination via remote sensing data. This paper presents the results of an experimental study in which the spectral dissimilarities of brown, green, blue-green and red algae were examined with a view to establishing a basis upon which broad changes in phytoplankton communities might be monitored through remote sensing. Pseudo phytoplankton communities were simulated in a series of mesocosm experiments from which spectral reflectance measurements were acquired. The results demonstrated that the phytoplankton colour groups examined were indeed spectrally dissimilar. The spectral distinction between colour groups was noted to be greatest at high concentrations of chlorophyll a and between pseudo-communities dominated by a single species; spectral differences were lower in mixed pseudo-communities with co-dominant species. Moreover, it proved possible to quantify the concentration of two potential biomarker pigments, fucoxanthin and C-phycocyanin, through the derivation of simple spectral indices. The coincidental presence of varying concentrations of SPM (SPIM and SPOM) caused significant attenuation of the spectral response of the pseudo-communities and affected the accuracy of biomarker pigment estimation. It is considered that the realisation of a remote sensing technique for the discrimination of phytoplankton taxa in inland waters would be an extremely useful tool for limnological research and water resource management and thus the future application of this research to inland waters is also discussed.