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1. Phytoplankton group-specific and community responses to co-limiting nutrients in a managed reservoir: Lake Murray, South Carolina

   https://doi.org/10.1093/plankt/fbaf003  

   Durbin, Haley; Cain, Ainsley; Madgett, Gavin; Knotts, Eilea; Pinckney, James (February 2025, Journal of Plankton Research)

   Beisner, Beatrix E (Ed.)

   Abstract Eutrophication is increasingly becoming a problem for freshwater lakes. We evaluated the effects of additions nitrate (N as NO3−) and phosphate (P as PO43−) on phytoplankton in a temperate lake reservoir (Lake Murray, South Carolina). High-performance liquid chromatography and ChemTax were used to measure concentrations of microalgal groups in the lake in 2021–2023 and bioassays. The phytoplankton community during the summer months consisted of green algae (37%), diatoms (27%), cryptophytes (20%), cyanobacteria (11%) and dinoflagellates (4%). Bioassays of N (20-μM NaNO3), P (10-μM KH2PO4) and N + P additions were conducted monthly from April to October 2023. All microalgal groups, except cyanobacteria, exhibited nutrient co-limitation with N as the primary limiting nutrient. Similarly, cyanobacteria exhibited co-limitation, but with P as the primary limiting nutrient. Nutrient additions of N + P (but not N or P singularly) also resulted in significant community shifts, with a strong response by green algae. The management implications for this study are that increases in N and P loading and ratio changes in the lake may result in major phytoplankton community changes toward dominance by green algae. However, increasing P loading relative to N may promote cyanobacterial growth over other phytoplankton groups in this lake system. 

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2. Effects of climate change and episodic heat events on cyanobacteria in a eutrophic polymictic lake.

   https://doi.org/10.1016/j.scitotenv.2019.07.220  

   Bartosiewicz, Maciej (January 2019, Science of the total environment)

   null (Ed.)

   Changes in mixing regimes and CO2 availability may promote harmful cyanobacterial blooms in polymictic lakes and ponds globally, but the underlying mechanisms still remain unclear. We integrated results from a natural experiment comprising an average-wet year (2011) and one with heat waves (2012), a long-term meteorological dataset (1960–2010), historical phosphorus concentrations and corresponding sedimentary pigment records, to determine, on different temporal scales, the mechanistic controls of cyanobacterial blooms in a eutrophic polymictic lake. Intense warming in 2012 was associated with: 1) increased stability of the water column with buoyancy frequencies exceeding 40 cph at the surface, 2) high phytoplankton biomass in spring (up to 125 mg WW L-1), 3) reduced downward transport of heat and 4) persistently depleted epilimnetic CO2 concentrations. CO2 depletion was effectively maintained by intense uptake by phytoplankton (influx up to 30 mmol m-2 d-1) in combination with reduced carbon inputs from the watershed during dry periods. Under eutrophic conditions these effects triggered massive bloom of buoyant cyanobacteria (up to 300 mg WW L-1). Complementary evidence from polynomial regression modelling using long-term datasets revealed that warming is the most important predictor of cyanobacterial abundance during the second half of the last century explaining 78% of the observed positive trend, whereas phosphorus concentration explained only 10% thereof. Together the results from the interannual comparison and the multi-decadal record indicate that hotter and drier climates increase water column stratification and decrease CO2 availability in eutrophic polymictic lakes. This combination catalyzes blooms of buoyant cyanobacteria. 

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3. The interaction of physical and biological factors drives phytoplankton spatial distribution in the northern California Current

   https://doi.org/10.1002/lno.11431  

   Krause, Jeffrey W.; Brzezinski, Mark A.; Largier, John L.; McNair, Heather M.; Maniscalco, Michael; Bidle, Kay D.; Allen, Andrew E.; Thamatrakoln, Kimberlee (February 2020, Limnology and Oceanography)

   Abstract Transitions in phytoplankton community composition are typically attributed to ecological succession even in physically dynamic upwelling systems like the California Current Ecosystem (CCE). An expected succession from a high‐chlorophyll (~ 10μg L⁻¹) diatom‐dominated assemblage to a low‐chlorophyll (< 1.0μg L⁻¹) non‐diatom dominated assemblage was observed during a 2013 summer upwelling event in the CCE. Using an interdisciplinary field‐based space‐for‐time approach leveraging both biogeochemical rate measurements and metatranscriptomics, we suggest that this successional pattern was driven primarily by physical processes. An annually recurring mesoscale eddy‐like feature transported significant quantities of high‐phytoplankton‐biomass coastal water offshore. Chlorophyll was diluted during transport, but diatom contributions to phytoplankton biomass and activity (49–62% observed) did not decline to the extent predicted by dilution (18–24% predicted). Under the space‐for‐time assumption, these trends infer diatom biomass and activity and were stimulated during transport. This is hypothesized to result from decreased contact rates with mortality agents (e.g., viruses) and release from nutrient limitation (confirmed by rate data nearshore), as predicted by the Disturbance‐Recovery hypothesis of phytoplankton bloom formation. Thus, the end point taxonomic composition and activity of the phytoplankton assemblage being transported by the eddy‐like feature were driven by physical processes (mixing) affecting physiological (release from nutrient limitation, increased growth) and ecological (reduced mortality) factors that favored the persistence of the nearshore diatoms during transit. The observed connection between high‐diatom‐biomass coastal waters and non‐diatom‐dominated offshore waters supports the proposed mechanisms for this recurring eddy‐like feature moving seed populations of coastal phytoplankton offshore and thereby sustaining their activity. 

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4. Tradeoffs between elemental homeostasis and growth govern freshwater phytoplankton responses to salinization

   https://doi.org/10.1002/lno.70099  

   Dias, Samuel_A_T; Prater, Clay; Diaz‐Delgado, Adriana; Clay, Natalie_A; Entrekin, Sally_A; Evans‐White, Michelle_A (June 2025, Limnology and Oceanography)

   Abstract Anthropogenic salinization resulting from road salt application can degrade aquatic environments by altering the structure and function of phytoplankton communities, ultimately reducing flows of resources through aquatic food webs. However, physiological mechanisms underlying taxon‐specific responses to salinization are often poorly linked to higher‐order ecosystem dynamics, limiting our ability to predict community responses to salinization. To this end, we tested hypotheses derived from Subsidy‐Stress and Ecological Stoichiometry theory by growing two cosmopolitan genera,Dolichospermum(prokaryotic, cyanobacteria) andScenedesmus(eukaryotic, green algae), across NaCl gradients and contrasting differences in their growth rates, degree of Na homeostasis, and cellular C : N : P ratios. We found mixed support for the subsidy‐stress hypothesis, with only stress responses observed for both species. Instead, growth declines appeared to be linked to stoichiometric tradeoffs between growth and homeostatic regulation, with stronger homeostatic Na regulation coinciding with a greater reduction inScenedesmusgrowth rates and higher variation in their stoichiometric C : N : P ratios across NaCl gradients. Nonhomeostatic Na regulation allowedDolichospermumto sustain higher growth rates, which appeared to constrain variation in their stoichiometric C : N : P ratios along with their stronger physiological regulation of intracellular P storage molecule production. Differences in phytoplankton growth responses were consistent with stoichiometric theory and field observations documenting shifts from green algae to cyanobacteria in response to freshwater salinization. Our results suggest that these shifts could take place below existing North American chronic threshold limits, resulting in decreased production at higher trophic levels by reducing phytoplankton biomass production rates and inducing nutritional stress in consumers. 

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5. Macro‐ and micronutrient effects on phytoplankton in Green Bay, Lake Michigan, and the western basin of Lake Erie

   https://doi.org/10.1111/jpy.13519  

   Stoll, Jordyn_T; Larson, James_H; Bailey, Sean_W; Blackwood, Christopher_B; Costello, David_M (December 2024, Journal of Phycology)

   Abstract Efforts to reduce the frequency, extent, and toxicity of harmful algal blooms (HABs) require knowledge about drivers of algal growth, toxin production, and shifts in phytoplankton community composition to cyanobacterial dominance. Although labile nitrogen (N) and phosphorus (P) fuel primary production, micronutrients also play roles as the enzymatic engines that facilitate rapid and efficient growth and toxin production. Macro‐ and micronutrient availability can shape community composition and function by selecting for particular taxa. To address how phytoplankton in two Great Lakes subbasins respond to macro‐ and micronutrients, we conducted bottle incubation enrichment experiments using water collected from two blooming and two nonblooming sites in Lakes Erie and Michigan during late summer (August). Three of the four sites exhibited multi‐nutrient limitation of growth. Both blooming sites responded strongest to enrichment. Both nonblooming sites responded the strongest to enrichment, and three of the four sites responded in some way to a mix of micronutrients (Fe, Mn, Mo, Ni, and Zn).Microcystis aeruginosarelative abundance increased most with N enrichment, while P enrichment increased the abundance of diatoms and chlorophytes. At the Fox River, N‐enriched communities grew 10%–20% more than non‐N enriched communities (measured as chlorophylla), and N‐enriched communities had, on average, over twice as much microcystin (non‐N communities average MC = 2.45 μg · L⁻¹, +N communities MC = 5.35 μg · L⁻¹). These overarching trends support the idea that control of HABs may not be effective with a P‐only approach. 

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