More Like this

1. Mitigating eutrophication and toxic cyanobacterial blooms in large lakes: The evolution of a dual nutrient (N and P) reduction paradigm

   https://doi.org/10.1007/s10750-019-04087-y  

   Paerl, H.W.; Havens, K.E.; Xu, H.; Zhu, G.; McCarthy, M.J.; Newell, S.E.; Scott, J.T.; Hall, N.S.; Otten, T.G.; Qin, B. (October 2019, Hydrobiologia)

   Cyanobacterial harmful algal blooms (CyanoHABs) are an increasingly common feature of large, eutrophic lakes. Non-N2-fixing CyanoHABs (e.g., Microcystis) appear to be proliferating relative to N2-fixing CyanoHABs in systems receiving increasing nutrient loads. This shift reflects increasing external nitrogen (N) inputs, and a[50-year legacy of excessive phosphorus (P) and N loading. Phosphorus is effectively retained in legacy-impacted systems, while N may be retained or lost to the atmosphere in gaseous forms (e.g., N2, NH3, N2O). Biological control on N inputs versus outputs, or the balance between N2 fixation versus denitrification, favors the latter, especially in lakes undergoing accelerating eutrophication, although denitrification removal efficiency is inhibited by increasing external N loads. Phytoplankton in eutrophic lakes have become more responsive to N inputs relative to P, despite sustained increases in N loading. From a nutrient management perspective, this suggests a need to change the freshwater nutrient limitation and input reduction paradigms; a shift from an exclusive focus on P limitation to a dual N and P colimitation and management strategy. The recent proliferation of toxic non-N2-fixing CyanoHABs, and ever-increasing N and P legacy stores, argues for such a strategy if we are to mitigate eutrophication and CyanoHAB expansion globally. 

   more » « less
2. Dual phosphorus and nitrogen nutrient reduction will be more effective than a phosphorus‐only reduction in mitigating diatom and cyanobacterial blooms in Lake Erie, USA –Canada

   https://doi.org/10.1002/lno.12719  

   Paerl, Hans W; Chaffin, Justin D; Cheshire, Jack H; Plaas, Haley E; Barnard, Malcolm A; Goerlitz, Lillian B; Braddy, Jeremy S; Sabo, Alexandrea; Nelson, Leah M; Yue, Lindsay (November 2024, Limnology and Oceanography)

   Abstract Lake Erie, USA–Canada, plays an important ecological and socioeconomic role but has suffered from chronic eutrophication. In particular, western Lake Erie (WLE) is the site of harmful algal blooms (HABs) which are suspected of being driven by excessive nutrient (phosphorus (P) and nitrogen (N)) inputs. During 2022 and 2023, in situ nutrient dilution and addition bioassays were conducted at a WLE bloom‐impacted location to investigate whether a nutrient reduction regime would be effective in limiting phytoplankton growth during the June diatom‐dominated spring blooms and August cyanobacteria‐dominated summer blooms. The primary objectives of this experiment were to (1) Determine if a proposed 40% P‐alone reduction would effectively reduce phytoplankton growth and mitigate blooms and (2) assess whether reductions in both P and N are more effective in controlling phytoplankton biomass than exclusive reductions in either N or P. Samples were analyzed for nutrient concentrations and growth rate responses for specific algal groups, utilizing diagnostic (for major algal groups) photopigments. Results indicated that although both 20% and 40% dilutions led to lower phytoplankton biomass and growth rates, 40% reductions were more effective. Our results support the USA–Canada Great Lakes Water Quality Agreement recommendation of a 40% P reduction, but also indicate that a parallel reduction of N input by 40% would be most effective in controlling bloom magnitudes. Overall, our findings underscore the recommendation that a year‐round dual N and P 40% reduction is needed for long‐term control of eutrophication and algal blooms, including cyanobacteria and diatoms, in Lake Erie. 

   more » « less
3. Influence of light, temperature, and nutrients on microcystin concentration during a winter cyanobacteria-dominated bloom

   https://doi.org/10.1093/plankt/fbaf061  

   Andersen, Isabelle M; Rusche, Katherine C; Voyles, Maggie E; Bros, Alexandra J; Knoll, Lesley B (October 2025, Journal of Plankton Research)

   Beisner, Beatrix E (Ed.)

   Abstract Freshwater ecosystems are increasingly at risk of experiencing toxin-producing cyanobacterial blooms during the winter due to anthropogenic nutrient loading and climate change. However, understanding how increased light, temperature and nutrient levels impact cyanotoxin production during the winter is limited, as most research has historically focused on blooms during the summer and fall. We conducted 2 × 2 × 2 incubation experiments in February and March to test the individual and interactive effects of light intensity (50 and 150 μmol m−2 s−1 PAR), elevated temperature (+3°C), and nitrogen and phosphorus enrichment on microcystin concentrations in a Planktothrix agardhii-dominated community sampled from Grand Lake Saint Mary’s, a hypereutrophic Ohio reservoir. Microcystin concentration significantly increased with elevated temperature in both months. In February, low light also promoted higher microcystin concentrations, particularly when combined with elevated temperature and nutrient enrichment. In March, nutrient enrichment had individual and interactive effects with temperature that caused higher microcystin concentrations. These results demonstrate that toxin-producing cyanobacteria are active in winter and that climate-driven changes in environmental conditions can interactively increase total toxin concentrations in the water column, even in the non-growing season. 

   more » « less
4. The ecology of cyanobacteria and their synergism with bacterioplankton in benthic mats under nutrient limitations in the Virgin River in Zion's National Park

   https://doi.org/10.1016/j.scitotenv.2025.180194  

   Sohrab, Abeer; Kaiser, Shadman; Bhattarai, Bishav; Stancheva, Rosalina; Goel, Ramesh (October 2025, Science of The Total Environment)

   Nitrogen (N) and Phosphorus (P) are essential nutrients which support cyanobacterial growth in lakes (as suspended cells or flocs) and flowing waters (as benthic mats). However, some toxic cyanobacteria can thrive even under depleted nutrient conditions. In this study, we investigated benthic toxic cyanobacterial mats in the Virgin River, Zion National Park, at two sites where visible benthic mats were observed at three different times. Our study focused on phosphorus and nitrogen cycling within these mats. The reactive P was below detection limits (<0.05 mg/L as P). Likewise, the dissolved inorganic N varied from below the detection limit to 0.06 mg/L as N. The relative abundance (based on total sequenced reads) of cyanobacteria ranged from 16.87 % to 50.02 % for samples from the Visitor's Center site and 10.34 % to 32.68 % for samples from the North Creek site with the presence of genera Microcoleus, Pseudoanabaena, Oscillatoria, Microcystis, and Cyanobium. The Visitors Center and North Creek sites shared several key heterotrophic bacteria, with Sandarakinorhabdus, Planctomyces, Brevundimonas, Thiomonas, and Pseudomonas being the most prominent ones. Notably, a toxic Microcoleus strain was identified in the nutrient-limited conditions of the Virgin River. This strain harbored an anatoxin-a biosynthesis gene cluster but lacked the anaK gene, suggesting limited toxin variability. We investigated the role of heterotrophic bacteria in nutrient cycling and their interactions with cyanobacterial populations within benthic mats of the Virgin River. Microcoleus and other cyanobacteria employed the Pho regulon, expressing genes such as pstS and alkaline phosphatase, to efficiently acquire organic phosphorus in low-nutrient environments. Nitrogen cycling also played a crucial role, with coexisting heterotrophic bacteria contributing to nitrogen fixation (nif gene) and assimilation, as well as denitrification (nosZ, nir, and nar genes). This research signifies the importance of integrated molecular approaches in unraveling nutrient cycling dynamics and toxin production mechanisms in benthic cyanobacterial mats. These insights are critical for understanding harmful cyanobacterial benthic blooms in freshwater ecosystems. 

   more » « less
5. Impacts of microbial assemblage and environmental conditions on the distribution of anatoxin-a producing cyanobacteria within a river network

   Bouma-Gregson, Keith; Olm, Matthew R.; Probst, Alexander J.; Anantharaman, Karthik; Power, Mary E.; Banfield, Jillian F. (January 2019, ISME)

   Blooms of planktonic cyanobacteria have long been of concern in lakes, but more recently, harmful impacts of riverine benthic cyanobacterial mats been recognized. As yet, we know little about how various benthic cyanobacteria are distributed in river networks, or how environmental conditions or other associated microbes in their consortia affect their biosynthetic capacities. We performed metagenomic sequencing for 22 Oscillatoriales-dominated (Cyanobacteria) microbial mats collected across the Eel River network in Northern California and investigated factors associated with anatoxin-a producing cyanobacteria. All microbial communities were dominated by one or two cyanobacterial species, so the key mat metabolisms involve oxygenic photosynthesis and carbon oxidation. Only a few metabolisms fueled the growth of the mat communities, with little evidence for anaerobic metabolic pathways. We genomically defined four cyanobacterial species, all which shared <96% average nucleotide identity with reference Oscillatoriales genomes and are potentially novel species in the genus Microcoleus. One of the Microcoleus species contained the anatoxin-a biosynthesis genes, and we describe the first anatoxin-a gene cluster from the Microcoleus clade within Oscillatoriales. Occurrence of these four Microcoleus species in the watershed was correlated with total dissolved nitrogen and phosphorus concentrations, and the species that contains the anatoxin-a gene cluster was found in sites with higher nitrogen concentrations. Microbial assemblages in mat samples with the anatoxin-a gene cluster consistently had a lower abundance of Burkholderiales (Betaproteobacteria) species than did mats without the anatoxin-producing genes. The associations of water nutrient concentrations and certain co-occurring microbes with anatoxin-a producing Microcoleus motivate further exploration for their roles as potential controls on the distributions of toxigenic benthic cyanobacteria in river networks. 

   more » « less