Bio-optical properties of the cyanobacterium Nodularia spumigena

Abstract

Abstract. In the last century, an increasing number of extreme weather events have been experienced across the globe. These events have also been linked to changes in water quality, especially due to heavy rains, flooding, or droughts. In terms of blue economic activities, harmful algal bloom events can pose a major threat, especially when they become widespread and last for several days. We present and discuss advanced measurements of a bloom dominated by the cyanobacterium Nodularia spumigena conducted by hyperspectral optical technologies via experiments of opportunity. Absorption coefficients, absorbance and fluorescence were measured in the laboratory, and these data are available at https://doi.org/10.4121/21610995.v1 (Wollschläger et al., 2022), https://doi.org/10.4121/21822051.v1 (Miranda et al., 2023) and https://doi.org/10.4121/21904632.v1 (Miranda and Garaba, 2023). Data used to derive the above-water reflectance are available from https://doi.org/10.4121/21814977.v1 (Garaba, 2023) and https://doi.org/10.4121/21814773.v1 (Garaba and Albinus, 2023). Additionally, hyperspectral fluorescence measurements of the dissolved compounds in the water were carried out. These hyperspectral measurements were conducted over a wide spectrum (200–2500 nm). Diagnostic optical features were determined using robust statistical techniques. Water clarity was inferred from Secchi disc measurements (https://doi.org/10.1594/PANGAEA.951239, Garaba and Albinus, 2022). Identification of the cyanobacterium was completed via visual analysis under a microscope. Full sequences of the 16S rRNA and rbcL genes were obtained, revealing a very strong match to N. spumigena; these data are available via GenBank: https://www.ncbi.nlm.nih.gov/nuccore/OP918142/ (Garaba and Bonthond, 2022b) and https://www.ncbi.nlm.nih.gov/nuccore/OP925098 (Garaba and Bonthond, 2022a). The chlorophyll-a and phycocyanin levels determined are available from https://doi.org/10.4121/21792665.v1 (Rohde et al., 2023). Our experiments of opportunity echo the importance of sustainable, simplified, coordinated and continuous water quality monitoring as a way to thrive with respect to the targets set in the United Nations Sustainable Development Goals (e.g. 6, 11, 12 and 14) or the European Union Framework Directives (e.g. the Water Framework Directive and Marine Strategy Framework Directive).