Improvement of In Vivo Fluorescence Tools for Fast Monitoring of Freshwater Phytoplankton and Potentially Harmful Cyanobacteria

Abstract

The use of multi-wavelength spectrofluorometers for the fast detection of algal taxa, based on chlorophyll a (Chl-a) emission spectra, has become a common practice in freshwater water management, although concerns about their accuracy have been raised. Here, inter-laboratory comparisons using monoalgal cultures have been performed to assess the reliability of different spectrofluorometer models, alongside Chl-a extraction methods. Higher Chl-a concentrations were obtained when using the spectrofluorometers than extraction methods, likely due to the poor extraction efficiencies of solvents, highlighting that traditional extraction methods could underestimate algal or cyanobacterial biomass. Spectrofluorometers correctly assigned species to the respective taxonomic group, with low and constant percent attribution errors (Chlorophyta and Euglenophyceae 6–8%, Cyanobacteria 0–3%, and Bacillariophyta 10–16%), suggesting that functioning limitations can be overcome by spectrofluorometer re-calibration with fresh cultures. The monitoring of a natural phytoplankton assemblage dominated by Chlorophyta and Cyanobacteria gave consistent results among spectrofluorometers and with microscopic observations, especially when cell biovolume rather than cell density was considered. In conclusion, multi-wavelength spectrofluorometers were confirmed as valid tools for freshwater monitoring, whereas a major focus on intercalibration procedures is encouraged to improve their reliability and broaden their use as fast monitoring tools to prevent environmental and public health issues related to the presence of harmful cyanobacteria.

Effects of Sampling Time and Depth on Phytoplankton Metrics in Agricultural Irrigation Ponds

“…Cell abundance correlations to photosynthetic pigments can also be affected by the fact that not all phytoplankton are equal in terms of producing photosynthetic pigments. This is the case for both cyanobacteria and eukaryotic algae where the concentration of phycocyanin or chlorophyll-a in a single cyanobacteria cell [26,76,77] and the concentration of chlorophyll-a in a single cell of eukaryotic algae [70,78,79] varies among species. Additionally, the nutritional state and status [80], growth phase [66,76], and cell size [81,82] may influence pigment concentrations and reliable enumerative capacity.…”

Water-Soluble Pyrolysis Products as Novel Urease Inhibitors Safe for Plants and Soil Fauna

“…The emergence and early growth of oats ( Avena sativa L.) were tested according to ISO 11269-2:2012 (see SI). Five endpoints were evaluated at the end of the test: (i) seed germination rate, reported as a percentage (%) relative to the control (distilled water), (ii) shoot length and (iii) shoot weight (mass of the five shoots in each pot after drying at 60 °C for 48 h), reported as percentages (%) relative to the control (distilled water), (iv) chlorophyll content (mg g –1 , after extraction with acetone and spectrophotometric analysis at 750 and 665 nm), , and (v) visible damages (chlorosis, necrosis, wilting, deformations).…”