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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 manual methods. While default calibration spectra may be acceptable for routine monitoring, we suggest a careful individual calibration of the DF spectrometer for basic research. The statistical methods developed here help to assess the adequacy of various calibration sets. [ABSTRACT FROM AUTHOR]

Summary 1. Cylindrospermopsis raciborskii occupies a rapidly expanding geographical area. Its invasive success challenges eutrophication control in many lakes. To understand better the load-dependent behaviour of this nitrogen fixing cyanobacterium under in situ conditions, we studied P-dependent growth of a C. raciborskii strain under continuous and pulsed P supply. 2. The Droop model reasonably described P-dependent growth in the continuously supplied chemostats. Large P pulses, however, caused a delay in growth and cells subject to P pulses grew slower than their counterparts with the same P quota supplied continuously. 3. The kinetics of P uptake indicated that C. raciborskii is opportunistic with respect to P. Its high excess P storage capacity after a saturating P pulse (Qex=95 µg P [mg C]-1) and P-specific uptake capacity (Umax = Vmax/QP=150–1200) are indicative of storage adaptation. At the same time, the affinity of the P uptake system (Umax/K = 800–4000) is also high. 4. Rate of leakage exceeded that of the steady state net P uptake by one to two orders of magnitude. Growth affinity of C. raciborskii (µmax/Kµ ≈ 20) was relatively low, presumably due to the substantial leakage. 5. The dynamics of the particular water body determine which trait contributes most to competitive success of C. raciborskii. In deep lakes with vertical nutrient gradients, the cyanobacterium may rely primarily on its high P storage capacity, which is coupled to a lack of short-term feedback inhibition and efficient buoyancy regulation. In lakes without such gradients, high P uptake affinity may be vitally important. [ABSTRACT FROM AUTHOR]