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1. Trends in Maumee River Nitrogen Loads and Their Complex Relationship to Harmful Algal Blooms in Western Lake Erie

   https://doi.org/10.3390/w18040465  

   Khan, Nusrat N; Paerl, Hans W; McCarthy, Mark J; Newell, Silvia E; Rudko, Noah; Muenich, Rebecca Logsdon (February 2026, Water)

   Nutrient runoff from agricultural activities in the watershed of Western Lake Erie (WLE) is a dominant driver of harmful algal blooms (HABs). While phosphorus (P) is a key factor causing these blooms and has been the focus for researchers and policymakers, the influence of nitrogen (N) on bloom dynamics has been overlooked. Total Kjeldahl N (TKN; organic N and ammonium N) has not been the focus of eutrophication research but was recently linked to bloom development in WLE. Here, monotonic and oscillatory statistical trend analyses were performed to interpret long-term (1982 to 2022) patterns of TKN in the Maumee River and were compared to algal biomass data as chlorophyll a. A predictive regression model used principal component analysis to estimate a chlorophyll-based index of HABs in WLE, and a systematic iterative process identified that TKN influences bloom dynamics along with soluble reactive phosphorus (SRP), total suspended solids (TSS) and flow. Although TKN loads exhibited a long-term decline, this decrease did not correspond to reduced HAB severity, reflecting the strong influence of flow-driven hydrologic variability on nutrient delivery and bloom response. The modeling results demonstrate that TKN, together with SRP, TSS, and flow, significantly contributes to predicting bloom magnitude. These findings highlight the need for dual-nutrient (N and P) management strategies and additional analyses of nutrient–hydrology interactions to improve HAB mitigation in WLE. 

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2. Rainstorm regimes modulate cyanobacterial bloom dynamics in deep reservoirs: Synergistic effects of nutrient pulses and hydrological perturbations

   https://doi.org/10.1002/lno.70222  

   Qiu, Yu; Xu, Hai; Zou, Wei; Zhu, Guangwei; Wu, Zhixu; Paerl, Hans W; Shi, Kun; Shi, Pengcheng; Kang, Lijuan; Zhao, Xingchen; et al (November 2025, Limnology and Oceanography)

   Abstract Global expansion of cyanobacterial harmful algal blooms, driven by anthropogenic nutrient loading and climate change, poses escalating threats to water security. While altered precipitation regimes are recognized as critical climate multipliers, their hierarchical controls on cyanobacterial harmful algal bloom dynamics remain poorly quantified, particularly in stratified reservoirs. Here, we integrate a 60‐yr (1961–2020) trend analysis of rainfall extremes with 4 yr (2017–2020) of high‐frequency monitoring of hydrology, nutrients, and phytoplankton through manual sampling and autonomous buoys in Lake Qiandaohu, a deep subtropical reservoir vital for drinking water in eastern China. Using Mann–Kendall trend analysis, random forest, and partial least squares path modeling, we elucidate the hierarchical mechanisms linking altered rainfall regimes to phytoplankton community shifts, with a focus on cyanobacterial harmful algal blooms. Our results reveal significant increases in both annual rainfall and rainstorm frequency over the past six decades, with peak events coinciding notably with early summer agricultural fertilization. Intensified early summer rainstorms triggered disproportionate phosphorus loading, significantly lowering N/P ratios and transiently suppressing cyanobacterial dominance. However, a critical approximately 20‐d lag period followed these events, wherein rapid thermal stratification recovery, combined with persistent legacy nutrients, selectively favored cyanobacterial proliferation. Furthermore, subsequent continuous dry‐hot spells amplified cyanobacterial dominance by enhancing water column stability and elevating temperatures. These findings reveal a paradoxical post‐storm vulnerability window that facilitates bloom formation in climate‐sensitive reservoirs. Given projected intensification of rainfall extremes under climate change, this study highlights the urgent need for integrated management strategies combining watershed nutrient control, meteorological forecasting, and adaptive reservoir operation to mitigate cyanobacterial harmful algal bloom risks. 

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3. More sustained, more severe blooms and shifting monthly patterns of the toxigenic dinoflagellate Karenia brevis on the West Florida Shelf

   https://doi.org/10.1016/j.hal.2025.102967  

   Glibert, Patricia M; Heil, Cynthia A; Li, Ming (December 2025, Harmful Algae)

   Various recent reports, based on different approaches, data sets and time periods, have yielded different conclusions with regard to whether blooms of the Florida red tide dino􀀙agellate, Karenia brevis, have increased over time. Without question, however, there have been a number of recent blooms that have been long lasting, continuing through the summer months normally taken to be outside the ideal temperature niche for K. brevis. Here, using a recently developed bloom severity index, the time series of blooms from 1970 to 2019 is examined, focusing on how monthly patterns have changed over time. More severe blooms have been found since the mid 1990s, now lasting 4- to 5-months longer than in previous decades, a trend related to the Oceanic Ni˜no Index (El Ni˜no -Southern Oscillation). Since the mid-1990s, water temperature anomalies have been related to bloom severity with lags of 3 to 6 months. The most signi􀀼cant temperature increases have occurred in the latter months of the year when K. brevis growth typically is highest. Increased 􀀙ow from the Caloosahatchee River, and its total nitrogen load, are also predictors of recent bloom severity with lags of several months. Cells that survive the nowwarmer winter dry season have adequate nutrients and may experience more favorable nitrogen forms as the summer wet season develops, and as nutrients are recycled, may “over summer”. The stresses of increased warming and increased nutrient pollution on K. brevis blooms will continue to make managing these blooms a challenge for management as climate change trajectories continue. 

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4. Climate shifts and anthropogenic footprints driving increased severity and duration of toxic Karenia brevis blooms in the Gulf of Mexico over the past ~50 years

   https://doi.org/10.3389/fmars.2026.1769349  

   Glibert, Patricia M; Heil, Cynthia A; Li, Ming (February 2026, Frontiers in Marine Science)

   Blooms of the toxigenic dinoflagellateKarenia brevisare an almost annual occurrence in the eastern Gulf of Mexico, typically initiating in late summer and early fall months and terminating in late spring or earlier. The question of whether blooms have been expanding in frequency or duration has long been debated. Recently, a Bloom Severity Index (BSI) was developed that captures changes in bloom magnitude based on cell concentrations normalized to maximum observed values. Here, changes in the BSI (severity and bloom duration) were examined for the period from 1970-2019, a period of rapid climate change and increased anthropogenic pressures. This time period encompassed several changes in the Oceanic Niño Index (the El Niño-Southern Oscillation), including a shift from a highly positive to a negative North Atlantic Oscillation in the mid 1990s, bringing with it increased precipitation and more intensive storms. Annual BSI and bloom duration have increased with increasing temperatures, and blooms have also become longer in duration in relation to increased temperatures and river flows since the mid 1990s. As increased precipitation is related to increased nutrient runoff, regional fertilizer use and the anthropogenic nitrogen (N) footprint based on population census data as proxies of nitrogen loads were examined. The duration of severe blooms was highly correlated with the increasing anthropogenic N footprint, especially when BSI values were averaged across multiple years. These relationships highlight the importance of climate changes and of increasing population since the 1980s and help to explain why earlier analyses of nutrient loads and bloom severity were inconclusive. To reduce bloom severity or duration in the future, reductions in N loads and releases from the Caloosahatchee River are needed more than ever to counteract the increasing pressures from climate change. 

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5. Genomic signatures of Lake Erie bacteria suggest interaction in the Microcystis phycosphere

   https://doi.org/10.1371/journal.pone.0257017  

   Hoke, Alexa K.; Reynoso, Guadalupe; Smith, Morgan R.; Gardner, Malia I.; Lockwood, Dominique J.; Gilbert, Naomi E.; Wilhelm, Steven W.; Becker, Isabella R.; Brennan, Grant J.; Crider, Katherine E.; et al (September 2021, PLOS ONE)

   Humbert, Jean-François (Ed.)

   Microbial interactions in harmful algal bloom (HAB) communities have been examined in marine systems, but are poorly studied in fresh waters. To investigate HAB-microbe interactions, we isolated bacteria with close associations to bloom-forming cyanobacteria, Microcystis spp., during a 2017 bloom in the western basin of Lake Erie. The genomes of five isolates ( Exiguobacterium sp. JMULE1, Enterobacter sp. JMULE2, Deinococcus sp. JMULE3, Paenibacillus sp. JMULE4, and Acidovorax sp. JMULE5.) were sequenced on a PacBio Sequel system. These genomes ranged in size from 3.1 Mbp ( Exiguobacterium sp. JMULE1) to 5.7 Mbp ( Enterobacter sp. JMULE2). The genomes were analyzed for genes relating to critical metabolic functions, including nitrogen reduction and carbon utilization. All five of the sequenced genomes contained genes that could be used in potential signaling and nutrient exchange between the bacteria and cyanobacteria such as Microcystis . Gene expression signatures of algal-derived carbon utilization for two isolates were identified in Microcystis blooms in Lake Erie and Lake Tai ( Taihu ) at low levels, suggesting these organisms are active and may have a functional role during Microcystis blooms in aggregates, but were largely missing from whole water samples. These findings build on the growing evidence that the bacterial microbiome associated with bloom-forming algae have the functional potential to contribute to nutrient exchange within bloom communities and interact with important bloom formers like Microcystis . 

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