Cyanobacterial Biovolume Research Articles

Monitoring of cyanobacterial breakthrough and accumulation by in situ phycocyanin probe system within full-scale treatment plants

Worldwide, there has been an increase in the presence of potentially toxic cyanobacterial blooms in drinking water sources and within drinking water treatment plants (DWTPs). The objective of this study is to validate the use of in situ probes for the detection and management of cyanobacterial breakthrough in high and low-risk DWTPs. In situ phycocyanin YSI EXO2 probes were devised for remote control and data logging to monitor the cyanobacteria in raw, clarified, filtered, and treated water in three full-scale DWTPs. An additional probe was installed inside the sludge holding tank to measure the water quality of the surface of the sludge storage tank in a high-risk DWTP. Simultaneous grab samplings were carried out for taxonomic cell counts and toxin analysis. A total of 23, 9, and 4 field visits were conducted at the three DWTPs. Phycocyanin readings showed a 93-fold fluctuation within 24 h in the raw water of the high cyanobacterial risk plant, with higher phycocyanin levels during the afternoon period. These data provide new information on the limitations of weekly or daily grab sampling. Also, different moving averages for the phycocyanin probe readings can be used to improve the interpretation of phycocyanin signal trends. The in situ probe successfully detected high cyanobacterial biovolumes entering the clarification process in the high-risk plant. Grab sampling results revealed high cyanobacterial biovolumes in the sludge for both high and low-risk plants.

Factors Affecting the Interpretation of Online Phycocyanin Fluorescence to Manage Cyanobacteria in Drinking Water Sources

Recently, in situ YSI EXO2 phycocyanin fluorescence probes have been widely deployed as a means to determine cyanobacterial abundance in drinking water sources, yet few studies have evaluated the effects of natural organic matter (NOM) and the ambient water temperature on the probe readings. In this study, Suwannee River NOM was added to laboratory cultivated cyanobacterial species to test the performance of the phycocyanin probe. The impact of temperature on phycocyanin fluorescence was evaluated by monitoring the laboratory cultivated cyanobacterial species and extracted phycocyanin pigment. Additionally, in situ phycocyanin fluorescence of the field samples from the water intake of a drinking water treatment plant (DWTP) in 2018 were compared with grab sample laboratory taxonomic analyses. We found: (1) the presence of Suwannee River NOM leads to the decrease in cell-bound cyanobacterial phycocyanin readings; (2) increasing ambient water temperature reduces dissolved and cell-bound cyanobacterial phycocyanin readings; (3) field study phycocyanin probe readings significantly correlated with the total cyanobacterial biovolume (R = 0.73, p < 0.1), and the relationship depends on the biovolume of dominant cyanobacterial species; (4) phycocyanin probe readings have a strong positive correlation with the natural light intensities; and (5) probe users should be fully aware of the sources of interferences when interpreting the results and apply the other physical-chemical parameters data simultaneously generated by the fluorometry to improve the probe’s measurements.

Year-long monitoring of phytoplankton community, toxigenic cyanobacteria, and total microcystins in a eutrophic tropical dam supplying the Mexico megacity

The Valle de Bravo dam is an important source of drinking water supply for the Mexico City Conurbation (>26 million inhabitants) and is also a hotspot for nautical sports, recreational fishing, and tourism. However, anthropogenic pressures in the upper reaches of the basin have led to increased eutrophication and numerous harmful cyanobacterial blooms (HCBs). To determine the effect of abiotic variables on the characteristics of the phytoplanktonic community, as well as their influence on the diversity of toxigenic cyanobacteria and related cyanotoxins, we evaluated monthly variations in environmental factors, phytoplankton biovolume and composition and total microcystins in Valle de Bravo dam during the year of 2019. Overall, 75 phytoplanktonic species were identified, mostly belonging to the divisions Cyanobacteria, Chlorophyta, and Bacillariophyta. Cyanobacteria presented the highest biomass throughout the year, with water temperature and rainfall being the best correlated factors. The highest concentrations of total microcystins were recorded from July to September (maximum of 71 μg L−1), associated with the dominance of species such as M. smithii, M. aeruginosa, M. viridis M. flos-aquae, Aphanocapsa planctonica, and Dolichospermum crassum, and environmental factors such as rainfall, total dissolved solids, water temperature, and specific trace metals. In all months except December, the total cyanobacterial biovolume was above the World Health Organization alert level two, indicating potentially high risks to human health. The predominance of cyanobacteria and high biovolumes classified water quality as poor to very poor during most of the year. To avoid the development of HCBs in this dam, the contribution of nutrients by the tributary rivers and sewage must be controlled, since the poor-quality conditions of the water threaten the aquatic biota, the sports and recreation activities and affect the potable water supply.

Phytoplankton Communities and Cyanotoxin Production in Some Bulgarian Lowland Lakes and Reservoirs

One of the most evident consequences of eutrophication of waters is the progressive spreading of persistent cyanobacterial blooms. They are often accompanied by the production of cyanotoxins in concentrations, which are hazardous for human health. In this research, we analysed phytoplankton communities in four lowland water bodies, for the presence of cyanobacterial blooms and toxin production. The cyanobacterial biovolumes we found, determine three of the lowland water bodies: Onogur Reservoir (OR), Asparuhov Val Reservoir (AVR), and Srebarna Lake (SL) as “Alert Level 1” of potentially hazardous levels of cyanotoxins. Cyanobacterial biovolume exceeds the threshold value of 8 mm3 L-1 (recreational waters) in AVR and SL at the end of the summer period. In OR, we registered sustainable bloom of Microcystis spp. during the whole summer season, and extremely high average seasonal value of the total biovolume (146.5 mm3 L-1). Micro-cystins were reported in all four analysed water bodies, with the highest concentration in OR (6 µg L-1). Cylindrospermopsin was detected in AVR and OR, while saxitoxins were in AVR and SL. The concentrations of cyanotoxins do not exceed the guideline values in recreational waters. However, the increased biovolumes of cyanobacteria are a signal that in three of the analysed water bodies, monitoring is recommended at the levels of cyanotoxins during the summer period.

Nuisance phytoplankton transport is enhanced by high flow in the main river for drinking water in Uruguay.

Eutrophication, climate change, and river flow fragmentation are the main cause of nuisance algal blooms worldwide. This study evaluated the conditions that trigger the growth and occurrence of nuisance phytoplankton in the Santa Lucía River, a subtropical floodplain lotic system that supplies drinking water to 60% of the population of Uruguay. The main variables that explained phytoplankton biovolume were extracted from generalized linear models (GLM). The potential impact of nuisance organism advection on water utility was estimated by the phytoplankton biovolume transport (BVTR, m3 day-1), an indicator of biomass load. Santa Lucía River had a wide flow range (0.7×105-1438×105 m3 day-1) and eutrophic conditions (median, TP: 0.139 mg L-1; TN: 0.589 mg L-1). GLMs indicated that phytoplankton biomass increased with temperature and soluble reactive phosphorus. Contrary to expectations, the presence of cyanobacteria was positively associated with periods of high flow that result in high cyanobacterial biovolume transport, with a probability of 3.35 times higher when flow increased by one standard deviation. The cyanobacterial biovolume transported (max: 9.5 m3 day-1) suggests that biomass was subsidized by allochthonous inocula. Biovolume from other nuisance groups (diatoms, cryptophytes, and euglenophytes) was positively associated with low-flow conditions and high nutrient concentrations in the main river channel, thereby indicating that these conditions boost eukaryote blooms. The evaluation of BVTR allows a better understanding of the dynamics of fluvial phytoplankton and can help to anticipate scenarios of nuisance species transport.

Micronutrients as growth limiting factors in cyanobacterial blooms; a survey of freshwaters in South East Australia

The role of trace metal micronutrients in limiting cyanobacterial growth and structuring the phytoplankton community is becoming more evident. However, little is known regarding the extent of micronutrient limitation in freshwaters or which micronutrient conditions favour potentially-toxic cyanobacteria. To assess how freshwater phytoplankton respond to micronutrient and macronutrient additions, we conducted nutrient amendment bioassays at seven sites across South Eastern-Australia. Sites were variable in cyanobacterial cell densities and phytoplankton community compositions. At two sites, Mannus Lake and Burrendong Dam, micronutrient additions (iron, cobalt, copper, manganese, molybdenum and zinc) increased cyanobacterial growth, indicating micronutrient limitation. Both sites had cyanobacterial blooms present at the onset of the experiment, dominated by Chrysosporum ovalisporum at Mannus Lake and Microcystis aeruginosa at Burrendong Dam. This suggests that micronutrients may be an important regulator of the severity of cyanobacterial blooms and may become limiting when there is high competition for nutrient resources. The addition of the micronutrient mixture resulted in a higher proportion of cyanobacteria compared to the control and a lower diversity community compared to phosphorus additions, indicating that micronutrients can not only influence cyanobacterial biovolume but also their ability to dominate the phytoplankton community. This reinforces that micronutrient requirements of phytoplankton are often species specific. As micronutrient enrichment is often overlooked when assessing nutrient-constraints on cyanobacterial growth, this study provides valuable insight into the conditions that may influence cyanobacterial blooms and the potential contribution of micronutrients to eutrophication.

Predicting cyanobacterial biovolumes from phycocyanin fluorescence using a handheld fluorometer in the field

Toxic cyanobacterial blooms are becoming more prevalent in freshwater systems, increasing the need for monitoring to protect human health. Phycocyanin fluorescence sensors have been developed as tools for providing fast and cost-effective proxy measurements for cyanobacterial biomass. However, poor precision and low sensitivity in many of the probe sensors assessed to-date has restricted their potential for practical application in cyanobacterial monitoring programmes. In the present study, the sensitivity and accuracy of a handheld fluorometer, the CyanoFluor, was assessed using 12 cyanobacterial strains and samples from four different lakes collected weekly for 12 weeks. After the initial measurements, the samples were lysed by sonication, which we hypothesised would reduce inter and intra-specific differences. The CyanoFluor displayed high sensitivity (limit of quantification = 3.5 µg L−1 of phycocyanin) and was able to detect cyanobacterial biovolumes to levels much lower than the threshold levels in current recreational guidelines worldwide. There were strong and significant phycocyanin to biovolume relationships (r2 ≥ 0.88, P < 0.05) for all 12 cyanobacterial cultures. Collectively, strong relationships between phycocyanin fluorescence and cyanobacterial biovolumes were also identified in environmental samples (r2 ≥ 0.78, P < 0.001), although weaker relationships were identified when lakes were analysed separately (r2 = 0.06 – 0.90). There were differences in phycocyanin per biovolume between both cultured strains and lakes, highlighting innate interspecific differences that exist between cyanobacterial species. Lysis of samples consistently reduced variability between technical replicates, in cyanobacteria cultures (up to 87% reduction in sample variability) and environmental samples (71 – 93% reduction), indicating that it would be a useful methodological step to improve the repeatability of results. When guideline thresholds (aligned with currently enforced risk assessment categories) were modelled based on the most successful linear regression model, 74% of samples were assigned to the correct risk category. The sensitivity of the CyanoFluor and accuracy of the phycocyanin threshold models, indicates high potential for this method to be integrated into cyanobacterial monitoring programmes.

Decreasing nitrogen loading and climate change promotes the occurrence of nitrogen-fixing cyanobacteria in a restored city lake

External loading reduction has been implemented to improve water quality in China since the 2000s. To evaluate the effects of nutrient reduction on phytoplankton, long-term monitoring data for Lake Wuli from 1998 to 2017 were analyzed. After the restoration since 2003, nitrogen decreased significantly from 8 to 2 mg/l until 2008 and then remained stable until 2017, while total phosphorus declined progressively from 0.2 mg/l to approximately 0.08 mg/l during 2003 and 2017. Biological data indicated that phytoplankton biovolume decreased after restoration until 2010 and then increased slightly from 2010 to 2017, mainly due to increasing of cyanobacterial biovolume. The dominant taxa shifted from cryptophyta to cyanobacteria since 2009. The results of both nonmetric multidimensional scaling and random forest regression showed that changes in nutrients, especially decreases in nitrogen, were the main drivers for phytoplankton community variation and increasing of cyanobacterial biovolume to the total phytoplankton biovolume ratio in summer and autumn. In addition to nutrients reduction, climatic variables such as wind speed decrease also played vital roles in increasing of cyanobacterial dominance in Lake Wuli. Our study confirmed that phytoplankton community respond strongly to nitrogen reduction in the subtropics and that climate change mediates the response.

Nitrogen fixation estimates for the Baltic Sea indicate high rates for the previously overlooked Bothnian Sea

Dense blooms of diazotrophic filamentous cyanobacteria are formed every summer in the Baltic Sea. We estimated their contribution to nitrogen fixation by combining two decades of cyanobacterial biovolume monitoring data with recently measured genera-specific nitrogen fixation rates. In the Bothnian Sea, estimated nitrogen fixation rates were 80 kt N year−1, which has doubled during recent decades and now exceeds external loading from rivers and atmospheric deposition of 69 kt year−1. The estimated contribution to the Baltic Proper was 399 kt N year−1, which agrees well with previous estimates using other approaches and is greater than the external input of 374 kt N year−1. Our approach can potentially be applied to continuously estimate nitrogen loads via nitrogen fixation. Those estimates are crucial for ecosystem adaptive management since internal nitrogen loading may counteract the positive effects of decreased external nutrient loading.

Quantifying the dependence of cyanobacterial growth to nutrient for the eutrophication management of temperate-subtropical shallow lakes

The increasing global occurrence of cyanobacterial blooms, attributed primarily to human-induced nutrient enrichment, significantly degrades freshwater ecosystems and poses serious risks to human health. The current study examined environmental variables and cyanobacterial biovolume (BCyano) of 28 shallow lakes in the eastern China plains during the spring and summer of 2018. We used a 95% quantile regression model to explore season-specific response of BCyano to total nitrogen (TN), or total phosphorus (TP), and robust linear relationships were observed between log(BCyano+0.001) and log(TN), or log(TP) in both spring and summer periods. Based on these regressions, regional-scale and season-specific TN and TP thresholds are proposed for these lakes to ensure the safety for recreational waters and drinking water source. However, actual BCyano for a given concentration of TN (or TP) for many observations were considerably lower than the results of the 95% regression model predict, indicating that other factors significantly modulated nutrient limitation of BCyano. Generalized additive model and quantile regression model were used together to explore potentially significant modulating factors, of which lake retention time, macrophytes cover and N: P ratio were identified as most important. Thus, it is necessary to develop type-specific nutrient thresholds with the consideration of these significant modulating factors. Furthermore, nutrient-BCyano relationships of our studied lakes with lake retention time>100 days and no macrophyte were further explored and nutrient thresholds of this lake type were proposed. Nutrient thresholds proposed in this study may play an essential role in achieving a cost-effective eutrophication management for shallow lakes both in the eastern China plains and elsewhere with similar climatic background. On a broader scale, the approaches and findings of this study may provide valuable reference to formulate reasonable nutrient reduction targets for other ecoregions with different climatic conditions.

Predicting cyanobacterial biovolume from water temperature and conductivity using a Bayesian compound Poisson-Gamma model

Eutrophication and climate change scenarios engender the need to develop good predictive models for harmful cyanobacterial blooms (CyanoHABs). Nevertheless, modeling cyanobacterial biomass is a challenging task due to strongly skewed distributions that include many absences as well as extreme values (dense blooms). Most modeling approaches alter the natural distribution of the data by splitting them into zeros (absences) and positive values, assuming that different processes underlie these two components. Our objectives were (1) to develop a probabilistic model relating cyanobacterial biovolume to environmental variables in the Río de la Plata Estuary (35°S, 56°W, n = 205 observations) considering all biovolume values (zeros and positive biomass) as part of the same process; and (2) to use the model to predict cyanobacterial biovolume under different risk level scenarios using water temperature and conductivity as explanatory variables. We developed a compound Poisson-Gamma (CPG) regression model, an approach that has not previously been used for modeling phytoplankton biovolume, within a Bayesian hierarchical framework. Posterior predictive checks showed that the fitted model had a good overall fit to the observed cyanobacterial biovolume and to more specific features of the data, such as the proportion of samples crossing three threshold risk levels (0.2, 1 and 2 mm³ L−1) at different water temperatures and conductivities. The CPG model highlights the strong control of cyanobacterial biovolume by nonlinear and interactive effects of water temperature and conductivity. The highest probability of crossing the three biovolume levels occurred at 22.2 °C and at the lowest observed conductivity (∼0.1 mS cm−1). Cross-validation of the fitted model using out-of-sample observations (n = 72) showed the model’s potential to be used in situ, as it enabled prediction of cyanobacterial biomass based on two readily measured variables (temperature and conductivity), making it an interesting tool for early alert systems and management strategies. Furthermore, this novel application demonstrates the potential of the Bayesian CPG approach for predicting cyanobacterial dynamics in response to environmental change.

Monitoring of cyanobacteria for water quality: doing the necessary right or wrong?

Cyanobacteria are an essential biological component of phytoplankton water quality assessment. However, there are some problems associated with the widely used everyday practices of sampling, estimation and use of cyanobacteria when calculating phytoplankton indices assessing water quality. Many indices were developed during the implementation of the Water Framework Directive, considered the most innovative European environmental legislation. Most indices include cyanobacteria as a composition or bloom metric. Problems with the indices concern the exclusion of most chroococcalean taxa from cyanobacterial biovolume estimations in lakes and reservoirs of the Mediterranean region, treatment of the mucilage of colonial chroococcalean taxa in biovolume estimations and overlooking of deep-water cyanobacterial blooms due to sampling depth. These problems may lead to a biased view of water quality. In this paper we argue in favour of including all cyanobacteria taxa and their mucilage in biovolume estimations and considering a sampling depth that covers deep-water maxima, such as those formed by Planktothrix rubescens or colonial chroococcalean taxa.

Combining national and state data improves predictions of microcystin concentration

Data collected from lakes at national (regional) scales and state (local) scales can provide different insights regarding relationships between environmental factors and biological responses, and combining these two types of data can potentially yield more precise and accurate understanding of ecological phenomena. National data can include many measures, cover large spatial areas, and span broad environmental gradients. Because of these characteristics, analyses of these data can yield accurate estimates of relationships among different lake characteristics. However, the number of samples in a national data set that is available for estimating a relationship specific to waterbodies within a smaller region, like a single state, is limited. Conversely, state monitoring data provide intensive sampling of lakes within a smaller area, but these data span a narrower range of conditions and may only include a subset of relevant measurements. Here, a Bayesian network model is described that represents the causal linkages between observations of chlorophyll a concentration, cyanobacterial biovolume, and microcystin concentration. This network model was fit to national data and provided a context for modeling observations of chlorophyll a and microcystin collected from lakes in Iowa. Using the knowledge inherent in the national network model improved the accuracy of predictions of microcystin concentrations in Iowa compared to a model based only on Iowa data.

Physical, biogeochemical, and meteorological factors responsible for interannual changes in cyanobacterial community composition and biovolume over two decades in a eutrophic lake

This study used a 20-year dataset (1995–2014) to identify factors affecting cyanobacterial community composition (CCC) and abundance in a eutrophic lake. We hypothesized that differences in thermal structure, nutrients, and meteorology drive interannual variability in CCC and abundance. Cluster analysis differentiated dominant cyanobacteria into rare, low abundance, or sporadically occurring taxa. The bloom-forming genera were Microcystis and Aphanizomenon, accounting for ~ 70% of total cyanobacterial biovolume (BV) on average, whereas unusually high abundance of Planktothrix, Synechococcus, and Oscillatoria were clear outliers in three of the years. Variability in CCC was significantly correlated (P 0.3) with ice duration, Kjeldahl nitrogen (TKN), and spring nitrite + nitrate (NO2+3); ice duration and TKN were associated with the occurrence of primarily non-bloom-forming genera. Pairwise correlations tested linear, exponential, and polynomial correlates of absolute and relative total Cyanophyta, Microcystis, or Aphanizomenon BV. TKN, total nitrogen (TN) and phosphorus (TP), TN:TP ratio, Schmidt stability, and rainfall correlated with total Cyanophyta, Microcystis, and Aphanizomenon BV, whereas ice cover, NO2+3, and TKN correlated with relative Microcystis and Aphanizomenon BV. Despite increasing TN:TP ratio over two decades, cyanobacterial abundance had not changed significantly. These data suggest differing responses of cyanobacterial genera to important environmental factors over two decades.

Survival of cyanobacteria in rivers following their release in water from large headwater reservoirs

Cyanobacterial survival following their release in water from major headwaters reservoirs was compared in five New South Wales rivers. Under low flow conditions, cyanobacterial presence disappeared rapidly with distance downstream in the Cudgegong and Hunter Rivers, whereas the other three rivers were contaminated for at least 300 km. Cyanobacterial survival is likely to be impacted by the geomorphology of each river, especially the extent of gravel riffle reaches (cells striking rocks can destroy them) and by the different turbulent flow conditions it produces within each. Flow conditions at gauging stations were used to estimate the turbulent strain rate experienced by suspended cyanobacteria. These indicate average turbulent strain rates in the Cudgegong and Hunter Rivers can be above 33 and 83 s−1 while for the Murray, Edward and Macquarie Rivers average strain rate was estimated to be less than 30 s−1. These turbulent strain rate estimates are substantially above published thresholds of approximately 2 s−1 for impacts indicated from laboratory tests. Estimates of strain rate were correlated with changes in cyanobacterial biovolume at stations along the rivers. These measurements indicate a weak but significant negative linear relationship between average strain rate and change in cyanobacterial biomass. River management often involves releasing cold deep water with low cyanobacterial presence from these reservoirs, leading to ecological impacts from cold water pollution downstream. The pollution may be avoided if cyanobacteria die off rapidly downstream of the reservoir, allowing surface water to be released instead. However high concentrations of soluble cyanotoxins may remain even after the cyanobacterial cells have been destroyed. The geomorphology of the river (length of riffle reaches) is an important consideration for river management during cyanobacterial blooms in headwater reservoirs.

Interactions between nitrogen form, loading rate, and light intensity on Microcystis and Planktothrix growth and microcystin production

The toxin-producing, bloom-forming cyanobacterial genera Microcystis and Planktothrix require fixed nitrogen (N), such as nitrate, ammonium, or organic N (e.g., urea) for growth and production of microcystins (MC). Bioavailable N can enter lakes in pulses via tributary discharge and through in-lake recycling, which can maintain low N concentrations. Additionally, light intensity has been suggested to play a role in MC production. This study examined how three forms of N (nitrate, ammonium, and urea) interacted with N loading rate (one large pulse vs. many small pulses) and light intensity to stimulate Microcystis and Planktothrix growth and MC production using nutrient enrichment experiments. Enrichments of nitrate, ammonium, and urea resulted in greater cyanobacterial biovolumes and MC concentrations than phosphorus-only enrichments, and there was no difference between pulse (100 μmol/L) and press treatments (8.3 μmol/L every 4 h). Analysis of mcyD transcripts showed significant up-regulation within 4 h of ammonium and urea enrichment. High light intensities (300 μmol photons/m2/s) with N enrichment resulted in greater cyanobacterial biovolumes and MC concentrations than lower light intensities (30 and 3 μmol photons/m2/s). Overall, the results suggest Microcystis and Planktothrix can use many forms of N and that high light intensities enhance MC production during elevated N concentrations. Moreover, the results here further demonstrate the importance of considering N, as well as P, in management strategies aimed at mitigating cyanobacterial blooms.

Increased risk of cyanobacterial blooms in northern high‐latitude lakes through climate warming and phosphorus enrichment

Abstract Harmful cyanobacterial blooms are an increasing problem at many locations throughout the world but are rarely reported in aquatic habitats at high latitudes. Shallow lakes are a major feature of northern permafrost landscapes and are likely to experience large‐scale changes in their limnological properties in the future as a consequence of climate warming. In the present study, we addressed the question of what preconditions would be necessary to stimulate the growth and dominance of bloom‐forming cyanobacteria in northern fresh waters. We analysed the summer phytoplankton of 18 lakes on eroding permafrost (thaw lakes) and on glacier‐scoured rock (rock basin lakes) in subarctic Quebec, Canada, to determine their phytoplankton community structure and the biomass contribution of cyanobacteria. This survey was complemented with an incubation experiment to evaluate the direct warming and indirect phosphorus (P) enrichment effects of climate change on cyanobacterial bloom development. All lakes contained diverse phytoplankton communities, often dominated by chrysophytes, dinoflagellates and chlorophytes. Cyanobacteria were present in all waterbodies, but their contribution to the total community biovolume was highly variable (mean of 8.7%, range 0.1%–47%). Cyanobacterial community biovolumes correlated positively with surface water temperatures, and negatively with dissolved organic carbon, soluble reactive phosphorus, iron and manganese concentrations in the surface waters. Phosphorus enrichment of water from a thaw lake resulted in a fourfold increase of chlorophyll a (Chl‐a) and an increase in the cyanobacterial pigments echinenone and zeaxanthin. The phytoplankton counts showed that there was a sharp decrease in diversity (expressed as decline of the Shannon–Wiener index from 1.69 to 0.16), accompanied by a shift to cyanobacterial dominance, notably by the heterocystous, potentially toxic species Dolichospermum cf. planctonicum. Increased temperature led to an initial doubling of cyanobacterial biovolume, followed by the development of a chrysophyte bloom. Combined warming and P enrichment led to reduced phytoplankton biodiversity, with a community composed of cyanobacteria and chrysophytes. There was also a pronounced response by the picophytoplankton community; picocyanobacteria were strongly stimulated by P enrichment, while picoeukaryotes increased in response to warming. The current inoculum levels of cyanobacteria in subarctic lakes and their responsiveness to temperature and phosphorus indicate the potential for an abrupt increase in their abundance, accompanied by a decrease in phytoplankton diversity. Ongoing climate change will increase the risk of noxious cyanobacterial blooms in northern lakes and ponds, with potentially negative consequences for higher trophic levels.

Sensor manufacturer, temperature, and cyanobacteria morphology affect phycocyanin fluorescence measurements.

Sensors to measure phycocyanin fluorescence in situ are becoming widely used as they may provide useful proxies for cyanobacterial biomass. In this study, we assessed five phycocyanin sensors from three different manufacturers. A combination of culture-based experiments and a 30-sample field study was used to examine the effect of temperature and cyanobacteria morphology on phycocyanin fluorescence. Phycocyanin fluorescence increased with decrease in temperature, although this varied with manufacturer and cyanobacterial density. Phycocyanin fluorescence and cyanobacterial biovolume were strongly correlated (R 2>0.83, P<0.05) for single-celled and filamentous species. The relationship was generally weak for a colonial strain of Microcystis aeruginosa. The colonial culture was divided into different colony size classes and phycocyanin measured before and after manual disaggregation. No differences were measured, and the observation that fluorescence spiked when large colonial aggregates drifted past the light source suggests that sample heterogeneity, rather than lack of light penetration into the colonies, was the main cause of the poor relationship. Analysis of field samples showed a strong relationship between in situ phycocyanin fluorescence and spectrophotometrically measured phycocyanin (R 2>0.7, P<0.001). However, there was only a weak relationship between phycocyanin fluorescence and cyanobacterial biovolume for two sensors (R 2=0.22-0.29, P<0.001) and a non-significant relationship for the third sensor (R 2=0.29, P > 0.4). The five sensors tested in our study differed in their output of phycocyanin fluorescence, upper working limits (1200 to >12,000μg/L), and responses to temperature, highlighting the need for comprehensive sensor calibration and knowledge on the limitations of specific sensors prior to deployment.

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.

Nutrient enrichment and vertical mixing mediate 2-methylisoborneol and geosmin concentrations in a drinking water reservoir

Few ecosystem-level studies have experimentally determined the physicochemical and biological factors that mediate concentrations of off-flavor compounds in drinking water reservoirs. Consequently, the watershed-scale mechanisms determining production of these compounds are still poorly understood. In a recent study, the addition of both nitrogen and phosphorus significantly increased 2-methylisoborneol (MIB). Not surprisingly, MIB was correlated with cyanobacterial abundance (a well-known producer of off-flavor compounds); however, MIB was most strongly correlated with diatom abundance. To empirically test for differences in the production of two important off-flavor compounds, specifically MIB and geosmin, by either cyanobacteria or diatoms, we conducted a fully factorial experiment that manipulated two factors that typically promote cyanobacteria (nitrogen and phosphorus fertilization) or diatoms (vertical mixing of the water column). As predicted, fertilization promoted cyanobacteria, and vertical mixing favored diatoms. Interestingly, the production of geosmin was rapid and consistent with an increase in cyanobacteria while MIB production increased later in the experiment when cyanobacterial biovolume tended to decline and diatom biovolume increased. Based on our current and previous studies, MIB and geosmin production is associated with cyanobacteria, but the direct or indirect influence of diatoms on production should not be ignored.