Bio-optical properties of cyanobacterium Nodularia spumigena

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, one major threat are harmful algal bloom events that tend to be widespread and can last up to several days. We present and discuss advanced measurements of a bloom involving the cyanobacterium Nodularia spumigena conducted by hyperspectral optical technologies through experiments-of-opportunity. Absorption coefficients, absorbance and fluorescence were measured in the laboratory and these are available via (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 is available via 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 done. The hyperspectral measurements were conducted over a wide spectrum (200–2500 nm). Identification of the cyanobacterium was completed by visual analyses under a microscope. Diagnostic optical features were determined using robust statistical techniques. Water clarity was inferred from Secchi disk measurements https://doi.org/10.1594/PANGAEA.951239 (Garaba and Albinus, 2022). Full sequences were obtained of the 16S rRNA and rbcL genes revealing a very strong match to Nodularia spumigena, data 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 in open-access 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 for the targets 2 set in the United Nations Sustainable Goals (e.g., Goals 6, 11, 12 and 14) or European Union Framework Directives (e.g. Water, Marine Strategy).