A reduced model of the fluorescence from the cyanobacterial photosynthetic apparatus designed for the in situ detection of cyanobacteria

An investigation of cyanobacteria, cyanotoxins and environmental variables in selected drinking water treatment plants in New Jersey

Harmful Algal Blooms (HAB) have the potential to impact human health primarily through their possible cyanotoxins production. While conventional water treatments can result in the removal of unlysed cyanobacterial cells and low levels of cyanotoxins, during severe HAB events, cyanotoxins can break through and can be present in the treated water due to a lack of adequate toxin treatment. The objectives of this study were to assess the HAB conditions in drinking water sources in New Jersey and investigate relationships between environmental variables and cyanobacterial communities in these drinking water sources. Source water samples were collected monthly from May to October 2019 and analyzed for phytoplankton and cyanobacterial cell densities, microcystins, cylindrospermopsin, Microcystis 16S rRNA gene, microcystin-producing mcyB gene, Raphidiopsis raciborskii-specific rpoC1 gene, and cylindrospermopsin-producing pks gene. Water quality parameters included water temperature, pH, dissolved oxygen, specific conductance, fluorescence of phycocyanin and chlorophyll, chlorophyll-a, total suspended solids, total dissolved solids, dissolved organic carbon, total nitrogen, ammonia, and total phosphorus. In addition to source waters, microcystins and cylindrospermopsin were analyzed for treated waters. The results showed all five selected New Jersey source waters had high total phosphorus concentrations that exceeded the established New Jersey Surface Water Quality Standards for lakes and rivers. Commonly found cyanobacteria were identified, such as Microcystis and Dolichospermum. Site E was the site most susceptible to HABs with significantly greater HAB variables, such as extracted phycocyanin, fluorescence of phycocyanin, cyanobacterial cell density, microcystins, and Microcystis 16S rRNA gene. All treated waters were undetected with microcystins, indicating treatment processes were effective at removing toxins from source waters. Results also showed that phycocyanin values had a significantly positive relationship with microcystin concentration, copies of Microcystis 16S rRNA and microcystin-producing mcyB genes, suggesting these values can be used as a proxy for HAB monitoring. This study suggests that drinking water sources in New Jersey are vulnerable to forthcoming HAB. Monitoring and management of source waters is crucial to help safeguard public health.

Growth conditions impact particulate absorption and pigment concentrations in two common bloom forming cyanobacterial species

Remote sensing using satellite imagery has been promoted as a method to broaden the scale and frequency of cyanobacterial monitoring. This relies on the ability to establish relationships between the reflectance spectra of water bodies and the abundance of cyanobacteria. A challenge to achieving this comes from a limited understanding of the extent to which the optical properties of cyanobacteria vary according to their physiological state and growth environment. The aim of the present study was to determine how growth stage, nutrient status and irradiance affect pigment concentrations and absorption spectra in two common bloom forming cyanobacterial taxa: Dolichospermum lemmermannii and Microcystis aeruginosa. Each species was grown in laboratory batch culture under a full factorial design of low or high light intensity and low, medium, or high nitrate concentrations. Absorption spectra, pigment concentrations and cell density were measured throughout the growth phases. The absorption spectra were all highly distinguishable from each other, with greater interspecific than intraspecific differences, indicating that both D. lemmermannii and M. aeruginosa can be readily differentiated using hyperspectral absorption spectra. Despite this, each species exhibited different responses in the per-cell pigment concentrations with varying light intensity and nitrate exposure. Variability among treatments was considerably higher in D. lemmermannii than in M. aeruginosa, which exhibited smaller changes in pigment concentrations among the treatments. These results highlight the need to understand the physiology of the cyanobacteria and to take caution when estimating biovolumes from reflectance spectra when species composition and growth stage are unknown.

The response of three typical freshwater algae to acute acid stress in water

The effect of acidic pH conditions on the physiological response of three typical freshwater algae, Chlorella vulgaris, Microcystis aeruginosa and Scenedesmus quadricauda, was investigated in this study. The results of the cultivation experiment indicated that the mortality of the three algae in the logarithmic growth phase increased with increasing exposure time and acidity under acute acidic conditions. The tolerance of S. quadricauda was stronger than that of the other two species under long-term (6 h) exposure to the same acidity; in contrast, C. vulgaris exhibited the greatest tolerance under short-term exposure conditions. The decrease in chlorophyll a (Chl a) content indicated that the photosynthesis of algae was inhibited under acid stress and that the algae could not continue to grow normally. This was consistent with the changes in lipid peroxidation and antioxidant enzyme activity, which were reflected by the malondialdehyde (MDA) content and superoxide dismutase (SOD) activity under acid stress, respectively. The results of this study demonstrated that when exposed to acute acidic conditions, the tolerance of three typical freshwater algae to acidity was significantly different. These findings provide valuable information for poorly mixed acidification operations designed to adjust the pH in lakes, reservoirs, or intake pipes of purification plants.

Light-induced fluorescence quenching leads to errors in sensor measurements of phytoplankton chlorophyll and phycocyanin

Optical sensors for fluorescence of chlorophyll a (f-Chl a) and phycocyanin (f-PC) are increasingly used as a proxy for biomass of algae and cyanobacteria, respectively. They provide measurements at high-frequency and modest cost. These sensors require site-specific calibration due to a range of interferences. Light intensity affects the fluorescence yield of cyanobacteria and algae through light harvesting regulation mechanisms, but is often neglected as a potential source of error for in-situ f-Chl a and f-PC measurements. We hypothesised that diel light variations would induce significant f-Chl a and f-PC suppression when compared to dark periods. We tested this hypothesis in a controlled experiment using three commercial fluorescence probes which continuously measured f-Chl a and f-PC from a culture of the cyanobacterium Dolichospermum variabilis as well as f-Chl a from a culture of the green alga Ankistrodesmus gracilis in a simulated natural light regime. Under light, all devices showed a significant (p<0.01) suppression of f-Chl a and f-PC compared to measurements in the dark. f-Chl a decreased by up to 79% and f-PC by up to 59% at maximum irradiance compared to dark-adapted periods. Suppression levels were higher during the second phase of the diel cycle (declining light), indicating that quenching is dependent on previous light exposure. Diel variations in light intensity must be considered as a significant source of bias for fluorescence probes used for algal monitoring. This is of high relevance as most monitoring activities take place during daytime and hence f-Chl a and f-PC are likely to be systematically underestimated under bright conditions. Compensation models, design modifications to fluorometers and sampling design are discussed as suitable alternatives to overcome light-induced fluorescence quenching.

Integrated Photonic System for Early Warning of Cyanobacterial Blooms in Aquaponics

Cyanobacterial blooms produce hazardous toxins, deplete oxygen, and secrete compounds that confer undesirable organoleptic properties to water. To prevent bloom appearance, the World Health Organization has established an alert level between 500 and 2000 cells·mL^-1, beyond the capabilities of most optical sensors detecting the cyanobacteria fluorescent pigments. Flow cytometry, cell culturing, and microscopy may reach these detection limits, but they involve both bulky and expensive laboratory equipment or long and tedious protocols. Thus, no current technology allows fast, sensitive, and in situ detection of cyanobacteria. Here, we present a simple, user-friendly, low-cost, and portable photonic system for in situ detection of low cyanobacterial concentrations in water samples. The system integrates high-performance preconcentration elements and optical components for fluorescence measurement of specific cyanobacterial pigments, that is, phycocyanin. Phycocyanin has demonstrated to be more selective to cyanobacteria than other pigments, such as chlorophyll-a, and to present an excellent linear correlation with bacterial concentration from 10² to 10⁴ cell·mL^-1 (R² = 0.99). Additionally, the high performance of the preconcentration system leads to detection limits below 435 cells·mL^-1 after 10 min in aquaponic water samples. Due to its simplicity, compactness, and sensitivity, we envision the current technology as a powerful tool for early warning and detection of low pathogen concentrations in water samples.

In-situ fluorescence monitoring of cyanobacteria: Laboratory-based quantification of species-specific measurement accuracy

In recent years, in-situ fluorometers have been extensively deployed to monitor cyanobacteria in near real-time. Acceptable accuracy can be achieved between measured pigments and cyanobacteria biovolume provided the cyanobacteria species are known. However, cellular photosynthetic pigment content and measurement interferences are site and species specific and can dramatically affect sensor reliability. We quantified the accuracy of an in-situ fluorometer compared with traditional methods using mono- and mixed cultures of four different cyanobacterial species. We found: (1) lower pigment content in cultures in stationary phase, (2) higher precision with the sensor compared to traditional pigment quantification methods of measuring phycocyanin and chlorophyll a, (3) species-specific relationships between sensor readings and measurements related to biovolume, (4) overestimation of pigments in mixed compared with mono cultures, (5) dissolved organic matter causing a loss in signal proportional to its degree of aromaticity, and (6) potential to quantify the degree of cell lysis with a fluorescent dissolved organic matter sensor. This study has provided important new information on the strengths and limitations of fluorescence sensors. The sensor readings can provide accurate biovolume quantification and species determination for a number of bloom-forming species when sensors are properly compensated and calibrated.

Early warning method for cyanobacteria toxin, taste and odor problems by the evaluation of fluorescence signals

Permanganate and ozone are often used in drinking water treatment plants for the oxidation of taste and odor compounds, toxins, and algae as well as the reduction of mussel activity. The disadvantage of an overuse of such oxidants is the potential lysis of cyanobacterial cells. Cell lysis causes taste and odor components as well as toxins to be released into the water, which results in the need for even more treatment to remove these compounds completely. Our research in the CLIENT-SIGN project investigated an innovative method to monitor the lysis of cyanobacteria cells: increases in a specific fluorescence emission spectrum of the cyanobacteria pigment phycocyanin were used as a proxy for cell lysis and other compounds (taste/odor, toxins) leaving the cells. We call this form of phycocyanin "free phycocyanin" or "unbound phycocyanin". By monitoring free phycocyanin via a relatively fast and inexpensive measurement, water utilities will be better able to optimize the dosage of pre-oxidation compounds to remove extracellular compounds while preventing the lysing of cells. Laboratory studies and a case study at Yangcheng Lake (adjacent to Lake Taihu, Yangcheng Lake Water Treatment Plant, Suzhou Industrial Park, China) are presented herein. An online surveillance system that monitors incoming raw water and the water after pre-oxidation is proposed to better cope with changing water conditions.

Effects of hairy crab breeding on drinking water quality in a shallow lake

The Yangcheng Lake, connected to Taihu, is partly served as drinking water source for Suzhou, China; the temporal and spatial changes of water quality parameters of it are investigated in this study. The Yangcheng Middle Lake with aquaculture area and the Yangcheng East Lake with important water intake are chosen to make a comparative investigation of the relationship between crab breeding and water quality. Phytoplankton community and the composition of dissolved organic matters (DOM) at different areas of the Yangcheng Lake are characterized with spectral fluorescence signatures. Results reveal that biopolymers and humic substances (HS) are the two major DOM compositions in the Yangcheng Lake. In the Yangcheng Middle Lake, the COD_Mn concentration at the large breeding area was lower than that in most other areas; while the concentration of algae and HS fluorescence intensity are positively correlated with each other in the Yangcheng Middle Lake. Crab breeding could accelerate nitrogen transformation and utilization. In summer and winter, the cumulative risk of building up potential harmful by-products such as DPBs caused by the biopolymers and HS is greater; the breeding of hairy crabs could reduce biopolymers and improve drinking water safety.

Fluorescence probes for real-time remote cyanobacteria monitoring: A review of challenges and opportunities

In recent years, there has been a widespread deployment of submersible fluorescence sensors by water utilities. They are used to measure diagnostic pigments and estimate algae and cyanobacteria abundance in near real-time. Despite being useful and promising tools, operators and decision-makers often rely on the data provided by these probes without a full understanding of their limitations. As a result, this may lead to wrong and misleading estimations which, in turn, means that researchers and technicians distrust these sensors. In this review paper, we list and discuss the main limitations of such probes, as well as identifying the effect of environmental factors on pigment production, and in turn, the conversion to cyanobacteria abundance estimation. We argue that a comprehensive calibration approach to obtain reliable readings goes well beyond manufacturers' recommendations, and should involve several context-specific experiments. We also believe that if such a comprehensive set of experiments is conducted, the data collected from fluorescence sensors could be used in artificial intelligence modelling approaches to reliably predict, in near real-time, the presence and abundance of different cyanobacteria species. This would have significant benefits for both drinking and recreational water management, given that cyanobacterial toxicity, and taste and odour compounds production, are species-dependent.

Calibration of an in-water multi-excitation fluorometer for the measurement of phytoplankton chlorophyll-a fluorescence quantum yield

A multi-excitation fluorometer (MFL, JFE Advantech Co., Ltd.), originally designed to discriminate between phytoplankton species present within a population, has been redirected for use in fluorescence quantum yield (FQY) determination. While this calibration for apparent FQY requires no modification of the MFL, it is necessary to have an independent measurement of the spectral absorption coefficient of the subject fluid. Two different approaches to calibration were implemented. The primary method made use of reference fluorescent dye solutions of known quantum yield. The second method made use of acrylic fluorescent plaques and films. The two methods yielded consistent results, except in the 570 and 590 nm LED channels of the MFL. Application of the MFL in FQY determination is illustrated with an in situ Southern Ocean sample.

An evaluation of a handheld spectroradiometer for the near real-time measurement of cyanobacteria for bloom management purposes

A commercially available handheld spectroradiometer, the WISP-3, was assessed as a tool for monitoring freshwater cyanobacterial blooms for management purposes. Three small eutrophic urban ponds which displayed considerable within-pond and between-pond variability in water quality and cyanobacterial community composition were used as trial sites. On-board algorithms provide field measurements of phycocyanin (CPC) and chlorophyll-a (Chl-a) from surface reflectance spectra measured by the instrument. These were compared with laboratory measurements. Although significant but weak relationships were found between WISP-3 measured CPC and cyanobacterial biovolume measurements and WISP-3 and laboratory Chl-a measurements, there was considerable scatter in the data due likely to error in both WISP-3 and laboratory measurements. The relationships generally differed only slightly between ponds, indicating that different cyanobacterial communities had little effect on the pigment retrievals of the WISP-3. The on-board algorithms need appropriate modification for local conditions, posing a problem if it is to be used extensively across water bodies with differing optical properties. Although suffering a range of other limitations, the WISP-3 has a potential as a rapid screening tool for preliminary risk assessment of cyanobacterial blooms. However, such field assessment would still require adequate support by sampling and laboratory-based analysis.

Assessment of in situ fluorometry to measure cyanobacterial presence in water bodies with diverse cyanobacterial populations

A YSI EXO2 water quality sonde fitted with fluorometric sensors for chlorophyll-a (Chl-a) and phycocyanin (CPC) was used to determine its applicability in cyanobacterial quantification in three small urban ponds in Sydney, Australia displaying considerable variations in cyanobacterial community composition and abundance, as well as eukaryotic algae, turbidity and chromophoric dissolved organic matter. CPC and Chl-a measured in situ with the instrument was compared against laboratory measures of cyanobacterial biovolume over two summer sampling periods. A good correlation was found between CPC and total cyanobacterial biovolume in two of the three ponds. The poor correlation in the third was due to the frequent dominance of picoplanktonic sized cyanobacteria. CPC did not correlate well with cell counts, and Chl-a was a poor measure of cyanobacterial presence. The relationship between CPC measured by fluorometry varied according to the dominant cyanobacterial taxa present in the ponds at any one time. Fluorometry has good potential for use in environmental monitoring of cyanobacterial biovolume, but may need to be based on predetermined relations applicable to local water bodies. Management guidelines based on CPC concentrations would also enhance the usefulness of in situ CPC measurements.

Application of a spectrofluorimetric tool (bbe BenthoTorch) for monitoring potentially toxic benthic cyanobacteria in rivers

Over the last decade reports of animal poisoning following accidental consumption of neurotoxin-producing benthic cyanobacteria (mainly Phormidium spp.) have increased. There is a need for rapid and cost-effective tools to survey benthic cyanobacteria. In this study we assessed the performance of the BenthoTorch, a fluorometric probe that provides in situ estimations of cyanobacteria, diatoms and green algae biomass in biofilms. Biofilms (n = 288) were analysed from two rivers in France and eight in New Zealand. Correlations between chlorophyll-a measured using the BenthoTorch and spectrophotometry were higher for thin (<2 mm) compared to thick (>2 mm) biofilms (r(2) = 0.58 and 0.27 respectively; p < 0.001). When cyanobacteria represented less than 50% of the total biomass (based on biovolumes), microscopic and BenthoTorch compositional estimations were significantly correlated (r(2) = 0.53, p < 0.001). Conversely, there was no correlation when cyanobacteria exceeded 50% of the total biomass. Under this scenario diatoms were overestimated. Our results suggest that the observed biases occur because the BenthoTorch only measures the upper biofilm layer and it underestimates the biomass of phycoerythrin-containing cyanobacteria. To improve the performance of this sensor and render it a useful tool for a rapid evaluation of benthic cyanobacterial biomass in rivers, we propose that: (i) the algorithms based on the LEDs responses currently available on this tool need revision, (ii) new excitation wavelengths should be included that allow the fingerprints of phycoerythrin-containing cyanobacteria to be discriminated, and (iii) a sensor that penetrates the biofilms is needed to obtain more accurate estimates of cyanobacterial biomass.

Quantitative analysis of extracted phycobilin pigments in cyanobacteria-an assessment of spectrophotometric and spectrofluorometric methods

Phycobilins are an important group of pigments that through complementary chromatic adaptation optimize the light-harvesting process in phytoplankton cells, exhibiting great potential as cyanobacteria species biomarkers. In their extracted form, concentrations of these water-soluble molecules are not easily determined using the chromatographic methods well suited to solvent-soluble pigments. Insights regarding the quantitative spectroscopic analysis of extracted phycobilins also remain limited. Here, we present an in-depth study of two methods that utilize the spectral properties of phycobilins in aqueous extracts. The technical work was carried out using high-purity standards of phycocyanin, phycoerythrin, and allophycocyanin. Calibration parameters for the spectrofluorometer and spectrophotometer were established. This analysis indicated the possibility of detecting pigments in concentrations ranging from 0.001 to 10 μg cm^-3. Fluorescence data revealed a reproducibility of 95 %. The differences in detection limits between the two methods enable the presence of phycobilins to be investigated and their amounts to be monitored from oligotrophic to eutrophic aquatic environments.

Using transcriptomics to improve butanol tolerance of Synechocystis sp. strain PCC 6803

Cyanobacteria are emerging as promising hosts for production of advanced biofuels such as n-butanol and alkanes. However, cyanobacteria suffer from the same product inhibition problems as those that plague other microbial biofuel hosts. High concentrations of butanol severely reduce growth, and even small amounts can negatively affect metabolic processes. An understanding of how cyanobacteria are affected by their biofuel product can enable identification of engineering strategies for improving their tolerance. Here we used transcriptome sequencing (RNA-Seq) to assess the transcriptome response of Synechocystis sp. strain PCC 6803 to two concentrations of exogenous n-butanol. Approximately 80 transcripts were differentially expressed at 40 mg/liter butanol, and 280 transcripts were different at 1 g/liter butanol. Our results suggest a compromised cell membrane, impaired photosynthetic electron transport, and reduced biosynthesis. Accumulation of intracellular reactive oxygen species (ROS) scaled with butanol concentration. Using the physiology and transcriptomics data, we selected several genes for overexpression in an attempt to improve butanol tolerance. We found that overexpression of several proteins, notably, the small heat shock protein HspA, improved tolerance to butanol. Transcriptomics-guided engineering created more solvent-tolerant cyanobacteria strains that could be the foundation for a more productive biofuel host.

Optimization of variable fluorescence measurements of phytoplankton communities with cyanobacteria

Excitation-emission fluorescence matrices of phytoplankton communities were simulated from laboratory-grown algae and cyanobacteria cultures, to define the optical configurations of theoretical fluorometers that either minimize or maximize the representation of these phytoplankton groups in community variable fluorescence measurements. Excitation sources that match the photosystem II (PSII) action spectrum of cyanobacteria do not necessarily lead to equal representation of cyanobacteria in community fluorescence. In communities with an equal share of algae and cyanobacteria, inducible PSII fluorescence in algae can be retrieved from community fluorescence under blue excitation (450-470 nm) with high accuracy (R (2) = 1.00). The highest correlation between community and cyanobacterial variable fluorescence is obtained under orange-red excitation in the 590-650 nm range (R (2) = 0.54). Gaussian band decomposition reveals that in the presence of cyanobacteria, the emission detection slit must be narrow (up to 10 nm) and centred on PSII chlorophyll-a emission (~683 nm) to avoid severe dampening of the signal by weakly variable phycobilisomal fluorescence and non-variable photosystem I fluorescence. When these optimizations of the optical configuration of the fluorometer are followed, both cyanobacterial and algal cultures in nutrient replete exponential growth exhibit values of the maximum quantum yield of charge separation in PSII in the range of 0.65-0.7.

Use of fluorescence fingerprints for the estimation of bloom formation and toxin production of Microcystis aeruginosa

The development of methods facilitating the detection of cyanobacterial blooms in drinking water reservoirs at an early stage is of great importance. Fluorescence spectroscopy could meet these requirements. The study contains the examination of possible correlations between the different maxima of a fluorescence excitation-emission matrix and the amount of produced and excreted toxins of a lab culture of Microcystis aeruginosa at different stages of growth. Various fluorescence signals (protein-like and humic-like substances, pigments) are suited for an estimation of cell density and actual intra- and extracellular toxin concentration. One signal at 315nm/396nm presumably originating from protein-like substances might be useful as a tool for the prediction of increasing cyanobacterial toxin concentrations. As the measurement of fluorescence matrices is still time consuming, synchronous scans with Deltalambda=80nm were tested as a potential alternative. They accurately depict the course of protein-like and humic-like fluorescence during the different stages of growth although especially the latter one is not captured at its maximum. However, due to insufficient separation of chlorophyll a and phycocyanin, the image of the matrix maxima by synchronous scans with Deltalambda=80nm can only be used with minor restrictions. Nevertheless, fluorescence spectroscopy seems to be a powerful tool for the evaluation of cyanobacterial blooms.

Establishment of an Alert Level Framework for cyanobacteria in drinking water resources by using the Algae Online Analyser for monitoring cyanobacterial chlorophyll a

The Algae Online Analyser (AOA) fluorometer simultaneously distinguishes four different phytoplankton groups by their specific fluorescence spectra and thus allows for real-time in-situ chlorophyll a measurements per algal group. This AOA was used for monitoring cyanobacterial chlorophyll a in the drinking water at the Bronisławow Bay abstraction point in Sulejow Reservoir (Poland). The main goal of this research was to develop an early warning method for the detection of cyanobacterial biovolume in the source water, in order to establish an Alert Level Framework for the drinking water abstraction point in Sulejow Reservoir. A positive correlation between cyanobacterial biovolume, as determined by conventional methods, and cyanobacterial chlorophyll a, as measured by the AOA, was found (p<0.05). The results of this study were used to determine threshold values for the Alert Level Framework, based on cyanobacterial chlorophyll a concentrations in the source water of Sulejow Reservoir. The presented threshold values are determined specifically for this abstraction point, but the principles can be applied to other locations.

Application of hydrogen peroxide for the removal of toxic cyanobacteria and other phytoplankton from wastewater

Phytoplankton blooms containing elevated levels of cyanobacteria are common in wastewatertreatment plants. Microcystis aeruginosa, the most common freshwater cyanobacterial species, produces the hepatotoxin microcystin, which is a threat to human and environmental health. Blooms also affect the viability of treating and reusing water and cause problems when detritus accumulates in pipe and pumping delivery infrastructure. We proposed the application of hydrogen peroxide (H2O2) to induce cyanobacterial cell death. Spectral fingerprinting of phytoplankton into four groups (cyanobacteria, chlorophyta, diatoms, and cryptophyta) allowed for determination of equivalent chlorophyll-a (chl-a) concentrations contributed by photosynthetic pigments, an indicative measure of the photosynthetic activity of each phytoplankton group. This was used to establish the effect of H2O2 addition on phytoplankton in wastewater samples. The lowest H2O2 dose that caused statistically significant exponential decay of phytoplankton groups was approximately 3.0 x 10(-3) g H2O2/microg phytoplankton chl-a. At this dose, cyanobacteria and total phytoplankton exhibited a half-life of 2.3 and 4.5 h, respectively. Cyanobacteria decayed at a rate approximately twice that of chlorophyta and diatoms, and the combined chl-a of all phytoplankton groups decreased to negligible levels within 48 h of H202 application.

Discrimination of phytoplankton classes using characteristic spectra of 3D fluorescence spectra

The discrimination of phytoplankton classes using the characteristic fluorescence spectra extracted from three-dimensional fluorescence spectra was investigated. Single species cultures of 11 phytoplankton species, representing 5 major phytoplankton divisions, were used. The 3D fluorescence spectra of the cultures grown at different temperatures (20 and 15 degrees C) and illumination intensities (140, 80 and 30 microM m(-2) s(-1)) were measured and their feature extraction methods were explored. Ordering Rayleigh and Raman scattering data as zero, the obtained excitation-emission matrices were processed by both singular value decomposition (SVD) and trilinear decomposition methods. The resulting first principal component can be regarded as the characteristic spectrum of the original 3D fluorescence spectrum. The analysis shows that such characteristic spectra have a discriminatory capability. At different temperatures, the characteristic spectra of Isochrysis galbana, Platymonas helgolanidica and Skeletonema costatuma have high degrees of similarity to their own species samples, while the spectra similarities of Alexandrium tamarense, Prorocentrum dentatum, Pseudo-nitzschia pungens, Chaetoceros curvisetus, Ch. Debilis, Ch. Didymus and Synechococcus sp. are not as significant as the other three species. C. curvisetus, Ch. Debilis and Ch. Didymus, belonging to genus Chaetoceros, have identical spectra and cannot be discriminated at all. Regarding all six diatom species as one class, the average discriminant error rate is below 9%. It is worth mentioning that the diatom class can be distinguished from A. tamarense and P. dentatum, which belong to Dinophyta.

Quantitative and qualitative evaluation of phytoplankton communities by trichromatic chlorophyll fluorescence excitation with special focus on cyanobacteria

We present results that were obtained with a newly developed fluorometer, the 'PhytoSensor'. They are based on multi-wavelength excitation of chlorophyll fluorescence to detect the phytoplankton biomass and to identify main taxons (among cyanobacteria, green and brown microalgae). A method to evaluate the photosynthetic potential of the phytoplankton was established. Attention was focused on the measurement of the cyanobacterial biomass. A modelling to distinguish between the two spectral groups (blue and red) of cyanobacteria as a function of their pigments and physiological status is proposed. The main innovation of the device results in the recording of the fluorescence induction kinetics of the phytoplankton to confirm and refine the evaluation of the taxonomic composition. The PhytoSensor abilities were compared with pigment analysis, commercial fluorometers, particle and microscopic counting and identification. The PhytoSensor has been used with success to monitor the dynamics of phytoplankton in drinking-water supply reservoirs in Southeast Asia.

Estimation of chlorophyll content and daily primary production of the major algal groups by means of multiwavelength-excitation PAM chlorophyll fluorometry: performance and methodological limits

The performance and methodological limits of the Phyto-PAM chlorophyll fluorometer were investigated with laboratory grown algae cultures and natural phytoplankton from the rivers Saar and Saale. The Phyto-PAM is a 4-wavelength chlorophyll fluorometer with the functional combination of chlorophyll (Chl) estimation and assessment of photosynthetic activity, both differentiated into the main algal groups. The reliability of fluorescence-based Chl estimation strongly depends on the group specific calibration of the instrument and the resulting chlorophyll/fluorescence (Chl/F) ratios in reference algal cultures. A very high reliability of the Chl estimation was obtained in the case of constant Chl/F-ratios. Algae grown at different light intensities showed marked differences in Chl/F-ratios, reflecting differences in pigment composition and Chl a specific absorption (a*). When the Phyto-PAM was calibrated with laboratory grown diatoms, the Chl a in river grown diatoms was underestimated, due a lower content of accessory pigments and stronger pigment packaging. While this aspect presently limits the application of PAM fluorometry in limnology, this limitation may be overcome by future technical progress in the detection of dynamic changes in Chl/F-ratio via fluorescence-based measurements of the functional PS II absorption cross-section. Practically identical Chl/F-ratios were found for the diatom-dominated waters of the rivers Saar and Saale, suggesting that the same instrument calibration parameters may be applied for hydrographically similar surface waters. For this particular case, despite of the present methodological limitations, the potential of PAM fluorometry in limnology could be demonstrated. Light response curves were measured to estimate primary production with a spectrally resolved model in daily courses at two sampling sites. Fluorescence based primary production was closely correlated with measured oxygen evolution rates until midday. In the afternoon, at the water surface the fluorescence approach gave higher rates than the measured oxygen evolution. Possible explanations for the observed differences are discussed.