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

Tackling Harmful Cyanobacterial Blooms with Chinese Colleagues: We're All in the Same Boat

Harmful cyanobacterial blooms (CyanoHABs) are a rapidly proliferating global problem, threatening the use and sustainability of our freshwater resources. In recent decades, the United States, China, and other developed and developing countries threatened by CyanoHAB expansion have established collaborative efforts aimed at mitigating and managing this environmental and human health problem. However, an escalating negative political climate and restrictive policies on scientific exchange threaten these efforts. In this Perspective, I point to progress that has been made to counter the CyanoHAB problem on U.S.-Chinese fronts through our collaborations, which have been mutually beneficial from research and academic perspectives. Much like global efforts now needed to control pandemics, we are all "in the same boat" when to comes to countering the threat CyanoHABs pose for drinkable, swimmable, and fishable freshwater supplies and human health.

Understanding the Differences in the Growth and Toxin Production of Anatoxin-Producing Cuspidothrix issatschenkoi Cultured with Inorganic and Organic N Sources from a New Perspective: Carbon/Nitrogen Metabolic Balance

Cyanotoxins are the underlying cause of the threat that globally pervasive Cyanobacteria Harmful algal blooms (CyanoHABs) pose to humans. Major attention has been focused on the cyanobacterial hepatotoxin microcystins (MCs); however, there is a dearth of studies on cyanobacterial neurotoxin anatoxins. In this study, we explored how an anatoxin-producing Cuspidothrix issatschenkoi strain responded to culture with inorganic and organic nitrogen sources in terms of growth and anatoxins production. The results of our study revealed that ʟ- alanine could greatly boost cell growth, and was associated with the highest cell productivity, while urea significantly stimulated anatoxin production with the maximum anatoxin yield reaching 25.86 μg/mg dry weight, which was 1.56-fold higher than that in the control group (BG11). To further understand whether the carbon/nitrogen balance in C. issatschenkoi would affect anatoxin production, we explored growth and toxin production in response to different carbon/nitrogen ratios (C/N). Anatoxin production was mildly promoted when the C/N ratio was within low range, and significantly inhibited when the C/N ratio was within high range, showing approximately a three-fold difference. Furthermore, the transcriptional profile revealed that anaC gene expression was significantly up-regulated over 2–24 h when the C/N ratio was increased, and was significantly down-regulated after 96 h. Overall, our results further enriched the evidence that urea can stimulate cyanotoxin production, and ʟ-alanine could boost C. issatschenkoi proliferation, thus providing information for better management of aquatic systems. Moreover, by focusing on the intracellular C/N metabolic balance, this study explained the anatoxin production dynamics in C. issatschenkoi in response to different N sources.

Predicting microcystin concentration action-level exceedances resulting from cyanobacterial blooms in selected lake sites in Ohio

Cyanobacterial harmful algal blooms and the toxins they produce are a global water-quality problem. Monitoring and prediction tools are needed to quickly predict cyanotoxin action-level exceedances in recreational and drinking waters used by the public. To address this need, data were collected at eight locations in Ohio, USA, to identify factors significantly related to observed concentrations of microcystins (a freshwater cyanotoxin) that could be used in two types of site-specific regression models. Real-time models include easily or continuously-measured factors that do not require that a sample be collected; comprehensive models use a combination of discrete sample-based measurements and real-time factors. The study sites included two recreational sites and six water treatment plant sites. Real-time models commonly included variables such as phycocyanin, pH, specific conductance, and streamflow or gage height. Many real-time factors were averages over time periods antecedent to the time the microcystin sample was collected, including water-quality data compiled from continuous monitors. Comprehensive models were useful at some sites with lagged variables for cyanobacterial toxin genes, dissolved nutrients, and (or) nitrogen to phosphorus ratios. Because models can be used for management decisions, important measures of model performance were sensitivity, specificity, and accuracy of estimates above or below the microcystin concentration threshold standard or action level. Sensitivity is how well the predictive tool correctly predicts exceedance of a threshold, an important measure for water-resource managers. Sensitivities > 90% at four Lake Erie water treatment plants indicated that models with continuous monitor data were especially promising. The planned next steps are to collect more data to build larger site-specific datasets and validate models before they can be used for management decisions.

Microcystis Bloom in an Urban Lake after River Water Diversion—A Case Study

To improve the water quality of Lake Yuehu, a water diversion from the Han River was conducted in July 2008. However, an unexpected Microcystis bloom occurred in the lake after water introduction. Water and sediment samples were collected from Lake Yuehu and the variation of chemical and biochemical parameters, as well as the phytoplankton community, were analyzed during the water diversion to assess its effect and to clarify the mechanism leading to the Microcystis bloom. The nitrogen (N) concentration was increased and phosphorus (P) concentration decreased in Lake Yuehu after receiving water from the Han River, which had a high loading of N and a low loading of P. These conditions may benefit the growth and dominance of non-N2 fixing Microcystis, as it may not have suffered from P limitation during our study because it did not produce extracellular phosphatase, which worked as an indicator of P deficiency, as evidenced by the in situ enzyme-labelled fluorescence. Notably, the sediment Fe (OOH)~P content significantly decreased in Lake Yuehu; this pulsed release of P from the sediment might have sustained the Microcystis bloom. Based on our results, algal blooms may occur as a consequence of conducting water diversion projects to improve water quality.

Nitrogen flux into metabolites and microcystins changes in response to different nitrogen sources in Microcystis aeruginosa NIES-843

The over-enrichment of nitrogen (N) in the environment has contributed to severe and recurring harmful cyanobacterial blooms, especially by the non-N₂ -fixing Microcystis spp. N chemical speciation influences cyanobacterial growth, persistence and the production of the hepatotoxin microcystin, but the physiological mechanisms to explain these observations remain unresolved. Stable-labelled isotopes and metabolomics were employed to address the influence of nitrate, ammonium, and urea on cellular physiology and production of microcystins in Microcystis aeruginosa NIES-843. Global metabolic changes were driven by both N speciation and diel cycling. Tracing ¹⁵ N-labelled nitrate, ammonium, and urea through the metabolome revealed N uptake, regardless of species, was linked to C assimilation. The production of amino acids, like arginine, and other N-rich compounds corresponded with greater turnover of microcystins in cells grown on urea compared to nitrate and ammonium. However, ¹⁵ N was incorporated into microcystins from all N sources. The differences in N flux were attributed to the energetic efficiency of growth on each N source. While N in general plays an important role in sustaining biomass, these data show that N-speciation induces physiological changes that culminate in differences in global metabolism, cellular microcystin quotas and congener composition.

Effect of intermittent aeration mode on nitrogen concentration in the water column and sediment pore water of aquaculture ponds

Nitrogen in pond sediments is a major water quality concern and can impact the productivity of aquaculture. Dissolved oxygen is an important factor for improving water quality and boosting fish growth in aquaculture ponds, and plays an important role in the conversion of ammonium-nitrogen (NH₄⁺-N) to nitrite-nitrogen (NO₂^--N) and eventually nitrate-nitrogen (NO₃^--N). A central goal of the study was to identify the best aeration method and strategy for improving water quality in aquaculture ponds. We conducted an experiment with six tanks, each with a different aeration mode to simulate the behavior of aquaculture ponds. The results show that a 36 hr aeration interval (T_c = 36 hr: 36 hr) and no aeration resulted in high concentrations of NH₄⁺-N in the water column. Using a 12 hr interval time (T_c = 12 hr: 12 hr) resulted in higher NO₂^--N and NO₃^--N concentrations than any other aeration mode. Results from an 8 hr interval time (T_c = 8 hr: 8 hr) and 24 hr interval time (T_c = 24 hr: 24 hr) were comparable with those of continuous aeration, and had the benefit of being in use for only half of the time, consequently reducing energy consumption.

An array microhabitat device with dual gradients revealed synergistic roles of nitrogen and phosphorous in the growth of microalgae

Harmful algal blooms (HABs) are an emerging environmental problem contaminating water resources and disrupting the balance of the ecosystems. HABs are caused by the sudden growth of photosynthetic algal cells in both fresh and marine water, and have been expanding in extent and appearing more frequently due to the climate change and population growth. Despite the urgency of the problem, the exact environmental conditions that trigger HABs are unknown. This is in part due to the lack of high throughput tools for screening environmental parameters in promoting the growth of photosynthetic microorganisms. In this article, we developed an array microhabitat device with well defined dual nutrient gradients suitable for quantitative studies of multiple environmental parameters in microalgal cell growth. This device enabled an ability to provide 64 different nutrient conditions [nitrogen (N), phosphorous (P), and N : P ratio] at the same time, and the gradient generation took less than 90 min, advancing the current pond and test tube assays in terms of time and cost. Using a photosynthetic algal cell line, Chlamydomonas reinhardtii, preconditioned in co-limited media, we revealed that N and P synergistically promoted cell growth. Interestingly, no discernible response was observed when single P or N gradient was imposed. Our work demonstrated the enabling capability of the microfluidic platform for screening effects of multiple environmental factors in photosynthetic cell growth, and highlighted the importance of the synergistic roles of environmental factors in algal cell growth.

Transcriptomic survey on the microcystins production and growth of Microcystis aeruginosa under nitrogen starvation

Cyanobacteria are a vital component of freshwater phytoplankton, and many species are recognized for their ability to produce toxins and harmful algal blooms (HABs). Nitrogen is an essential element of all the complex macromolecules in algal cells. However, the underlying molecular mechanism of the changes in transcriptomic patterns and physiological responses in response to N starvation is poorly understood. The transcriptomes were generated via RNA-sequencing (RNA-Seq) technology to study the major metabolic pathway under N starvation. The results shed light on the mechanism of toxin production and physiological adaptations in Microcystis aeruginosa (M. aeruginosa). The cell density gradually increased during the first two days then declined over time and was finally stable at (15.50 ± 0.5) × 10⁵ cell mL^-1 after 6 days. The chlorophyll-a content and phycocyanin content of M. aeruginosa increased during the first two days and subsequently decreased markedly over time under N starvation. The variable to maximum chlorophyll fluorescence ratio (F_v/F_m ratio) decreased with time under N starvation. Most photosynthesis genes have similarity decreasing trends with growth physiological changes. The microcystins (MCs) levels generally increased first, reaching a peak value with 1.35 pg cell^-1 on the fifth day, and then remained roughly constant. The genes involved in N metabolism-related gene expression were upregulated to maintain normal biological activity, while the genes involved in photosynthesis-related gene expression were downregulated to save energy. All genes encoding algae toxin synthesis were upregulated under N starvation. The observed expression patterns demonstrate that all MCs genes respond similarly to MCs production within the cell. Our results indicate the response mechanism of M. aeruginosa under N starvation and provide a comprehensive understanding of N-controlling cyanobacteria and MCs synthesis.

Nitrogen availability facilitates phosphorus acquisition by bloom-forming cyanobacteria

Cyanobacterial blooms are threatening freshwater ecosystems. The physiological basis involved in the onset of cyanobacterial bloom is fundamental to advance in bloom predictions. Generally, cyanobacteria grow until the availability of nitrogen (N), phosphorus (P) or both nutrients becomes limited. Population survival may depend on physiological adjustments to nutrient deficiency as well as on the efficient use of episodic N and P inputs. This study investigated the effect of N inputs on phosphate uptake affinity and activity of N-deficient bloom-forming cyanobacteria. Lake samples dominated by filamentous cyanobacteria were preincubated with and without nitrate addition, and the uptake of [32P] phosphate pulses was measured in the following days. Phosphate uptake kinetics were analyzed with a flow-force model that provides the threshold concentration, reflecting phosphate uptake affinity, and the membrane conductivity coefficient that corresponds to the activity of uptake systems. After 24 h of nitrate preincubation, phosphate uptake kinetics showed a progressive increase in affinity (nanomolar [Pe]A) and activity (25-fold) concomitant with cyanobacterial growth. It was demonstrated that the alleviation of N-deficiency by N inputs boosts the activation of phosphate uptake systems of non-N2-fixing cyanobacteria to sustain growth. Therefore, reduction of dissolved inorganic N levels in lakes is also mandatory to limit cyanobacterial phosphate uptake affinity and activity capabilities.

A space-time geostatistical model for probabilistic estimation of harmful algal bloom biomass and areal extent

Harmful algal blooms (HABs) have been increasing in intensity worldwide, including the western basin of Lake Erie. Substantial efforts have been made to track these blooms using in situ sampling and remote sensing. However, such measurements do not fully capture HAB spatial and temporal dynamics due to the limitations of discrete shipboard sampling over large areas and the effects of clouds and winds on remote sensing estimates. To address these limitations, we develop a space-time geostatistical modeling framework for estimating HAB intensity and extent using chlorophyll a data sampled during the HAB season (June-October) from 2008 to 2017 by five independent monitoring programs. Based on the Bayesian information criterion for model selection, trend variables explain bloom northerly and easterly expansion from Maumee Bay, wind effects over depth, and variability among sampling methods. Cross validation results demonstrate that space-time kriging explains over half of the variability in daily, location-specific chlorophyll observations, on average. Conditional simulations provide, for the first time, comprehensive estimates of overall bloom biomass (based on depth-integrated concentrations) and surface areal extent with quantified uncertainties. These new estimates are contrasted with previous Lake Erie HAB monitoring studies, and deviations among estimates are explored and discussed. Overall, results highlight the importance of maintaining sufficient monitoring coverage to capture bloom dynamics, as well as the benefits of the proposed approach for synthesizing data from multiple monitoring programs to improve estimation accuracy while reducing uncertainty.

High Diversity of Microcystin Chemotypes within a Summer Bloom of the Cyanobacterium Microcystis botrys

The fresh-water cyanobacterium Microcystis is known to form blooms world-wide, and is often responsible for the production of microcystins found in lake water. Microcystins are non-ribosomal peptides with toxic effects, e.g. on vertebrates, but their function remains largely unresolved. Moreover, not all strains produce microcystins, and many different microcystin variants have been described. Here we explored the diversity of microcystin variants within Microcystis botrys, a common bloom-former in Sweden. We isolated a total of 130 strains through the duration of a bloom in eutrophic Lake Vomb, and analyzed their microcystin profiles with tandem mass spectrometry (LC-MS/MS). We found that microcystin producing (28.5%) and non-producing (71.5%) M. botrys strains, co-existed throughout the bloom. However, microcystin producing strains were more prevalent towards the end of the sampling period. Overall, 26 unique M. botrys chemotypes were identified, and while some chemotypes re-occurred, others were found only once. The M. botrys chemotypes showed considerable variation both in terms of number of microcystin variants, as well as in what combinations the variants occurred. To our knowledge, this is the first report on microcystin chemotype variation and dynamics in M. botrys. In addition, our study verifies the co-existence of microcystin and non-microcystin producing strains, and we propose that environmental conditions may be implicated in determining their composition.

A Multiplex Analysis of Potentially Toxic Cyanobacteria in Lake Winnipeg during the 2013 Bloom Season

Lake Winnipeg (Manitoba, Canada), the world’s 12th largest lake by area, is host to yearly cyanobacterial harmful algal blooms (cHABs) dominated by Aphanizomenon and Dolichospermum. cHABs in Lake Winnipeg are primarily a result of eutrophication but may be exacerbated by the recent introduction of dreissenid mussels. Through multiple methods to monitor the potential for toxin production in Lake Winnipeg in conjunction with environmental measures, this study defined the baseline composition of a Lake Winnipeg cHAB to measure potential changes because of dreissenid colonization. Surface water samples were collected in 2013 from 23 sites during summer and from 18 sites in fall. Genetic data and mass spectrometry cyanotoxin profiles identified microcystins (MC) as the most abundant cyanotoxin across all stations, with MC concentrations highest in the north basin. In the fall, mcyA genes were sequenced to determine which species had the potential to produce MCs, and 12 of the 18 sites were a mix of both Planktothrix and Microcystis. Current blooms in Lake Winnipeg produce low levels of MCs, but the capacity to produce cyanotoxins is widespread across both basins. If dreissenid mussels continue to colonize Lake Winnipeg, a shift in physicochemical properties of the lake because of faster water column clearance rates may yield more toxic blooms potentially dominated by microcystin producers.

Interspecies interactions between Microcystis aeruginosa PCC 7806 and Desmodesmus subspicatus SAG 86.81 in a co-cultivation system at various growth phases

In lakes, cyanobacterial blooms are frequently associated with green algae and dominate the phytoplankton community in successive waves. In the present study, the interactions between Microcystis aeruginosa PCC 7806 and Desmodesmus subspicatus were studied to clarify the probable ecological significance of algal secondary metabolites; focusing on the role of cyanotoxin 'microcystin-LR' (MC-LR). A dialysis co-cultivation technique was applied where M. aeruginosa was grown inside and D. subspicatus was cultured outside of the dialysis tubing. The concentration of the intra- and extracellular MC-LR and the growth of two species were measured at different time points over a period of one month. Additionally, the growth of the two species in the culture filtrate of one another and the effect of the purified MC-LR on the growth of the green alga were studied. The results indicated that the co-existing species could affect each other depending on the growth phases. Despite the early dominance of D. subspicatus during the logarithmic phase, M. aeruginosa suppressed the growth of the green alga at the stationary phase, which coincided with increased MC production and release. However, the inhibitory effects of Microcystis might be related to its other extracellular metabolites rather than, or possibly in addition to, MC.

Metatranscriptomic Analyses of Diel Metabolic Functions During a Microcystis Bloom in Western Lake Erie (United States)

This study examined diel shifts in metabolic functions of Microcystis spp. during a 48-h Lagrangian survey of a toxin-producing cyanobacterial bloom in western Lake Erie in the aftermath of the 2014 Toledo Water Crisis. Transcripts mapped to the genomes of recently sequenced lower Great Lakes Microcystis isolates showed distinct patterns of gene expression between samples collected across day (10:00 h, 16:00 h) and night (22:00 h, 04:00 h). Daytime transcripts were enriched in functions related to Photosystem II (e.g., psbA), nitrogen and phosphate acquisition, cell division (ftsHZ), heat shock response (dnaK, groEL), and uptake of inorganic carbon (rbc, bicA). Genes transcribed during nighttime included those involved in phycobilisome protein synthesis and Photosystem I core subunits. Hierarchical clustering and principal component analysis (PCA) showed a tightly clustered group of nighttime expressed genes, whereas daytime transcripts were separated from each other over the 48-h duration. Lack of uniform clustering within the daytime transcripts suggested that the partitioning of gene expression in Microcystis is dependent on both circadian regulation and physicochemical changes within the environment.

Evaluation of the use of eucalyptus to control algae bloom and improve water quality

Lakes represent an important source of drinking water resource for human beings. The presence of harmful algae blooms can pose a serious threat to lakes water quality. This study explored the feasibility of using eucalyptus plants and leaves extracts for controlling algae proliferation in an aquatic milieu. After 30 days of treatment, the inhibitory efficiencies were 85.8% and 20.9% for treatments planting eucalyptus and eucalyptus leaves extracts, respectively. The synergistic effects of allelopathy and competitive absorption for macro nutrients were attributed to the effective control of algae proliferation in the mesocosm systems. Moreover, the analysis of microbial community structures indicated that eucalyptus plants or leaves extracts had no adverse effect on species diversity and their relative abundance. The choice of using eucalyptus to control algae bloom will be dictated by environmental and economic considerations within a geographical region.

Evaluation of changes in Microcystis aeruginosa growth and microcystin production by urea via transcriptomic surveys

The freshwater cyanobacteria, Microcystis aeruginosa (M. aeruginosa), is well known to produce microcystins (MCs) and induce the formation of harmful algal blooms (HABs) in aquatic environments, but the effects that urea fertilizer has on cyanobacterial growth and toxin production from a molecular biology perspective remain poorly understood. We evaluated changes in the growth and toxicity of M. aeruginosa cultured under different conditions of nitrogen (N) starvation (NN), low nitrogen (LN), and high nitrogen (HN). Cell density and chlorophyll-a concentrations decreased in cyanobacteria exposed to N starvation and increased following the addition of urea, whereas MCs content increased to a peak and then decreased after urea addition. Transcriptomic analysis confirmed that most genes encoding MCs and genes involved in N metabolic pathways were upregulated under N starvation and LN conditions, whereas these genes were downregulated under HN conditions. Our results offer important insights into the exploring N in controlling the formation of HABs and toxin production based on both physiological and molecular response.

Succession and interaction of surface and subsurface cyanobacterial blooms in oligotrophic/mesotrophic reservoirs: A case study in Miyun Reservoir

Subsurface cyanobacterial blooms, are a significant source of odor problems in source water and have been recorded in many oligotrophic/mesotrophic drinking water reservoirs. In this study, we explored the key driving forces responsible for the succession between surface and subsurface cyanobacteria using ecological niche modelling based upon a case study in Miyun Reservoir, China. The results suggest a negative effect of water depth and surface light irradiance (I₀) on subsurface Planktothrix sp. growth (p-values < 0.001), and a unimodal effect of surface water temperature (T₀) with the optimum at 23 °C (p-value < 0.001). While the surface Microcystis spp. shows a strong positive relationship with temperature (T₀; p-value < 0.001), and significant effects for the interaction between T₀ and I₀ (p- value < 0.01). In addition, we identified the extent and type of interaction between subsurface and surface cyanobacteria and conclude that the high irradiance surface water combined with sufficient nutrients at the pre-bloom stage are key factors responsible for the preferential growth of surface cyanobacteria, while the gradual decline of the surface cyanobacteria in post-bloom stage is associated with nutrient reduction. This decline and loss of surface populations enhanced underwater irradiance and thus promoted the growth and allowed for succession of subsurface cyanobacteria in deeper layers where the nutrient supply was still adequate. Based upon this, the growth potentials for the subsurface and surface cyanobacteria are different under different environmental conditions: the subsurface cyanobacteria have greater growth potential than surface cyanobacteria in shallow oligotrophic and deep eutrophic reservoirs during median light irrigation seasons.

Ammonium recycling supports toxic Planktothrix blooms in Sandusky Bay, Lake Erie: Evidence from stable isotope and metatranscriptome data

Sandusky Bay, Lake Erie, receives high nutrient loadings (nitrogen and phosphorus) from the Sandusky River, which drains an agricultural watershed. Eutrophication and cyanobacterial harmful algal blooms (cyanoHABs) persist throughout summer. Planktothrix agardhii is the dominant bloom-forming species and the main producer of microcystins in Sandusky Bay. Non-N₂ fixing cyanobacteria, such as Planktothrix and Microcystis, thrive on chemically reduced forms of nitrogen, such as ammonium (NH₄⁺) and urea. Ammonium regeneration and potential uptake rates and total microbial community demand for NH₄⁺ were quantified in Sandusky Bay. Potential NH₄⁺ uptake rates in the light increased from June to August at all stations. Dark uptake rates also increased seasonally and, by the end of August, were on par with light uptake rates. Regeneration rates followed a similar pattern and were significantly higher in August than June. Ammonium uptake kinetics during a Planktothrix-dominated bloom in Sandusky Bay and a Microcystis-dominated bloom in Maumee Bay were also compared. The highest half saturation constant (K_m) in Sandusky Bay was measured in June and decreased throughout the season. In contrast, K_m values in Maumee Bay were lowest at the beginning of summer and increased in October. A significant increase in V_max in Sandusky Bay was observed between July and the end of August, reflective of intense competition for depleted NH₄⁺. Metatranscriptome results from Sandusky Bay show a shift from cyanophycin synthetase (luxury NH₄⁺ uptake; cphA1) expression in early summer to cyanophycinase (intracellular N mobilization; cphB/cphA2) expression in August, supporting the interpretation that the microbial community is nitrogen-starved in late summer. Combined, our results show that, in late summer, when nitrogen concentrations are low, cyanoHABs in Sandusky Bay rely on regenerated NH₄⁺ to support growth and toxin production. Increased dark NH₄⁺ uptake late in summer suggests an important heterotrophic contribution to NH₄⁺ depletion in the phycosphere. Kinetic experiments in the two bays suggest a competitive advantage for Planktothrix over Microcystis in Sandusky Bay due to its higher affinity for NH₄⁺ at low concentrations.

Reduced forms of nitrogen are a driver of non-nitrogen-fixing harmful cyanobacterial blooms and toxicity in Lake Erie

Western Lake Erie (WLE) experiences anthropogenic eutrophication and annual, toxic cyanobacterial blooms of non-nitrogen (N) fixing Microcystis. Numerous studies have shown that bloom biomass is correlated with an increased proportion of soluble reactive phosphorus loading from the Maumee River. Long term monitoring shows that the proportion of the annual Maumee River N load of non-nitrate N, or total Kjeldahl nitrogen (TKN), has also increased significantly (Spearman's ρ = 0.68, p = 0.001) over the last few decades and is also significantly correlated to cyanobacterial bloom biomass (Spearman's ρ = 0.64, p = 0.003). The ratio of chemically reduced N to oxidized N (TKN:NO3) concentrations was also compared to extracted chlorophyll and phycocyanin concentrations from all weekly sampling stations within WLE from 2009 to 2015. Both chlorophyll (Spearman's ρ = 0.657, p < 0.0001) and phycocyanin (Spearman's ρ = 0.714, p < 0.0001) were significantly correlated with TKN:NO3. This correlation between the increasing fraction of chemically reduced N from the Maumee River and increasing bloom biomass demonstrates the urgent need to control N loading, in addition to current P load reductions, to WLE and similar systems impacted by non-N-fixing, toxin-producing cyanobacteria.

Dominance and Growth Factors of Pseudanabaena sp. in Drinking Water Source Reservoirs, Southern China

Pseudanabaena sp. is a common and harmful species in freshwater cyanobacteria blooms. There are very few studies on its distribution characteristics and growth influencing factors. In the current study, it was found to be dominant in three cascading reservoirs in Southern China. Field observations and laboratory experiments were integrated to investigate the dominance and growth factors of Pseudanabaena sp. The effects of temperature, light intensity, nutrients, chemical oxygen demand (COD), pH, and disturbance on Pseudanabaena sp. growth were evaluated. The results indicated that Pseudanabaena sp. had significant positive correlations with water temperature, pH, and COD (p < 0.01) and a positive correlation with NH3-N (p < 0.05). The optimum growth temperature range for Pseudanabaena sp. was from 20 to 30 °C; hence, it usually has outbreaks in May and August. The optimum light intensity and pH for Pseudanabaena sp. were 27 μmol photons m−2s−1 and from 7 to 9, respectively. The superior tolerance for low light, disturbance, and phosphorus deficiency of Pseudanabaena sp. may be the main factors affecting its dominance in reservoirs. Controlling nitrogen was more effective than controlling phosphorus to avoid the risk that was brought by Pseudanabaena sp. This study contributed to the theoretical knowledge for the prediction and control of the growth of Pseudanabaena sp.

Accuracy of data buoys for measurement of cyanobacteria, chlorophyll, and turbidity in a large lake (Lake Erie, North America): implications for estimation of cyanobacterial bloom parameters from water quality sonde measurements

Microcystin (MCY)-producing harmful cyanobacterial blooms (cHABs) are an annual occurrence in Lake Erie, and buoys equipped with water quality sondes have been deployed to help researchers and resource managers track cHABs. The objective of this study was to determine how well water quality sondes attached to buoys measure total algae and cyanobacterial biomass and water turbidity. Water samples were collected next to two data buoys in western Lake Erie (near Gibraltar Island and in the Sandusky subbasin) throughout summers 2015, 2016, and 2017 to determine correlations between buoy sonde data and water sample data. MCY and nutrient concentrations were also measured. Significant (P < 0.001) linear relationships (R² > 0.75) occurred between cyanobacteria buoy and water sample data at the Gibraltar buoy, but not at the Sandusky buoy; however, the coefficients at the Gibraltar buoy differed significantly across years. There was a significant correlation between buoy and water sample total chlorophyll data at both buoys, but the coefficient varied considerably between buoys and among years. Total MCY concentrations at the Gibraltar buoy followed similar temporal patterns as buoy and water sample cyanobacterial biomass data, and the ratio of MCY to cyanobacteria-chlorophyll decreased with decreased ambient nitrate concentrations. These results suggest that buoy data are difficult to compare across time and space. Additionally, the inclusion of nitrate concentration data can lead to more robust predictions on the relative toxicity of blooms. Overall, deployed buoys with sondes that are routinely cleaned and calibrated can track relative cyanobacteria abundance and be used as an early warning system for potentially toxic blooms.

Mitigating the Expansion of Harmful Algal Blooms Across the Freshwater-to-Marine Continuum

Anthropogenic nutrient overenrichment, coupled with rising temperatures, and an increasing frequency of extreme hydrologic events (storms and droughts) are accelerating eutrophication and promoting the expansion of harmful algal blooms (HABs) across the freshwater-to-marine continuum. All HABs-with a focus here on cyanobacterial blooms-pose serious consequences for water supplies, fisheries, recreational uses, tourism, and property values. As nutrient loads grow in watersheds, they begin to compound the effects of legacy stores. This has led to a paradigm shift in our understanding of how nutrients control eutrophication and blooms. Phosphorus (P) reductions have been traditionally prescribed exclusively for freshwater systems, while nitrogen (N) reductions were mainly stressed for brackish and coastal waters. However, because most systems are hydrologically interconnected, single nutrient (e.g., P only) reductions upstream may not necessarily reduce HAB impacts downstream. Reducing both N and P inputs is the only viable nutrient management solution for long-term control of HABs along the continuum. This article highlights where paired physical, chemical, or biological controls may improve beneficial uses in the short term, and offers management strategies that should be enacted across watershed scales to combat the global expansion of HABs across geographically broad freshwater-to-marine continua.