Continuous monitoring of phytoplankton dynamics in Lake Balaton (Hungary) using on‐line delayed fluorescence excitation spectroscopy

Abstract

1. This study introduces delayed fluorescence (DF) excitation spectroscopy as an on-line tool for in situ monitoring of the composition and biomass of various colour classes of phytoplankton when they are photosynthetically active (cyanobacteria, chlorophytes, chromophytes and cryptophytes). The DF data are validated by comparison with those from conventional methods (weekly microscopic counts and the measurement of chlorophyll concentration). 2. The composition of phytoplankton as assessed by DF agreed reasonably well with the results from microscopic counts, particularly when differences in chlorophyll-specific DF integrals of the various colour classes were taken into account. 3. Integrals of DF spectra were converted into concentration of chlorophyll a using empirical factors derived from field data. The value of the conversion factor was nearly twice as high when the relative abundance of cyanobacteria was low (<15%) than when it was high. The converted DF-chl time series agreed well with chlorophyll measurements particularly when blooms were developing. As the DF method is inherently free of the interference caused by pigment degradation products, the discrepancy between the two data sets increased during the collapse of blooms and when sediment resuspension was intense. 4. Fourier spectrum analysis of the time series of DF-chl indicated that samples must be taken, at a minimum, every 2-3 days to capture the dynamics of phytoplankton. As a consequence, the dynamics of various algal blooms, including their timing, duration and net growth rate, could be estimated with greater confidence than by using conventional methods alone. 5. On-line DF spectroscopy is an advanced technique for monitoring daily the biomass and composition of the photosynthetically active phytoplankton in aquatic environments, including turbid shallow lakes. At present, the detection limit is around 1 mg DF-chl a m )3 in terms of total biomass but confidence in estimates of phytoplankton composition declines sharply below about 5 mg chl a m )3 . 6. On-line DF spectroscopy represents a promising approach for monitoring phytoplankton. It will be useful in water management where it can act as an early-warning system of declines in water quality. In basic ecological research it can supplement

Gut content microbiota of introduced bigheaded carps ( Hypophthalmichthys spp.) inhabiting the largest shallow lake in Central Europe

“…However, it should be noted that phytoplankton has characteristic seasonal dynamics with changing biomass and composition in the temperate climate zone, therefore its importance as a food resource for fish may also differ substantially across seasons and ecosystems. In general, eukaryotic algae dominate the phytoplankton in Lake Balaton, and cyanobacteria proliferate substantially only in August and September (Istvánovics et al, 2005). Since pyrosequencing analysis was performed on samples taken in June, identification of plastid sequences added relevant information to our study.…”

Modeling the Effect of Waves on the Diurnal Temperature Stratification of a Shallow Lake

“…Basic measurements were obtained from the hydrometeorological monitoring station (Keszthely) operated by the MTA-BME Water Management Research Group [32] in the western bay of the lake, near the shoreline. Here, the mean depth is 1.4 m. Water temperature is monitored at 5 depths (surface, bottom and 3 probes in between).…”

New approach in studies of microalgal cell lysis

“…The sensitivity of DF intensity in this study was no more than several 100 living cells ml -1 , but a higher sensitivity could be achieved by using bigger sample volumes and a detection system, which enables higher detection of delayed fluorescence light (Montecino et al, submitted for publication). An additional advantage of the delayed fluorescence technique is that it can distinguish among several algal taxonomic groups by using DF excitation spectra [15,26]. For example, monitoring changes in phytoplankton composition during growth enables better analysis and interpretation of the measured data.…”

“…Both methods are selective for photosynthetic organisms, thus reducing the problems with the background from other sources (e.g. heterotrophic bacteria, zooplankton, and abiotic substances) or autofluorescence [15]. Most importantly, the methods do not require any sample pretreatment or other manipulation before the measurement.…”

“…They plotted the decrease in optical density at 570 nm (which was linearly correlated to cell concentration) and the increase in absorbance of filtrates at 420 nm (which was linearly correlated to the cell lysis and pigment release). TLS detects released pigments from the lysed cells [11,12], whereas the DF measures the biomass of living algal cells [13][14][15][16][17]. Both methods are selective for photosynthetic organisms, thus reducing the problems with the background from other sources (e.g.…”