Chlorophyll-a and phycocyanin concentrations from a Nodularia spumigena bloom event on Lake Bante in Wilhelmshaven, Germany

Lake Bante in Germany was surveyed on 25 August 2022 and the gathered water samples were filtered through 0.2 µm pore sized Whatman Nuclepore Track-Etch membranes with a diameter of 47 mm. The filters were frozen and stored at -80 °C until further analyses. These frozen filters were transferred to a 20 mL glass vial followed by addition of 5 mL 1 × phosphate buffered saline with a pH = 7 to obtain pigments concentrations. An ultrasonic bath filled with crushed ice was used to sonicate the samples for 4 times in 60 second pulses with 60 second pauses in between the sonication. The sample glass vials were then centrifuged and 3 × 250 µL of the supernatant was transferred onto a 96 microwell plate. Sample absorbance was obtained using a BioTek Instruments Synergy H1 Hybrid Multi-mode microplate reader. Phycocyanin concentrations (µg/L) were derived following the recommended steps (Horváth et al., 2013). The remaining supernatant was decanted and the filters were refrozen at -22°C. Samples were freeze-dried for 24 h and then 5 mL of 99.5% ethanol were added to each glass vial. The alcoholic extracts were prepared as explained above. Again the samples were centrifuged and the supernatant from each sample was measured in the microplate reader. Chlorophyll a concentrations (mg/L) was estimated as described by Ritchie, 2008.