Globally-expanding, nutrient-driven harmful cyanobacterial blooms (CyanoHABs) are additionally modulated by climatic changes impacting freshwater-marine continua. In 2022-2023, the San Francisco Bay Delta, California's main freshwater source and important biodiversity refuge, experienced record sequential drought and flood years, which altered seasonal CyanoHABs in a hydrologically-stable Delta CyanoHAB "hot spot". We observed a severe bloom in 2022 (drought year) followed by bloom-free conditions in 2023 (flood year), despite elevated nutrient loads in 2023. In situ bioassays revealed nutrient dilution by elevated freshwater discharge in 2023 controlled CyanoHABs, independent of flushing dynamics. Findings show nutrient concentrations, not nutrient loads, impact the CyanoHAB hotspot in the short-term while nutrient loading determines long-term trophic state. Climate-modulated nutrient variability will likely affect future nutrient-bloom dynamics in waterbodies worldwide; thus nutrient reduction strategies should consider hydrology-mediated nutrient concentration patterns.

We evaluated the use of low-cost air quality sensors (PurpleAir) and satellite-derived indicators of ocean color (CyAN) in the study of aerosol emissions from cyanobacterial blooms.

Cyanobacterial harmful algal blooms (CyanoHABs) are a major concern for water quality, public health and viability of aquatic ecosystems. Increased inputs of nutrients, i.e., nitrogen (N) and phosphorus (P), are known to amplify the occurrence, severity, and duration of CyanoHABs. There is growing concern that CyanoHABs are proliferating along the freshwater to marine continuum, including throughout estuaries. We assessed the influence of nutrient enrichment on the abundance and composition of CyanoHABs and accompanying phytoplankton communities in the San Francisco Bay Delta (SFBD) estuarine ecosystem, a vital resource for California's water supply, fisheries, and recreation. In situ nutrient addition bioassays were conducted in June and September 2022, at the end of a record three-year drought period, and May and August 2023, an extremely high rainfall and discharge year. Water was collected from two locations in the SFBD recognized for having CyanoHAB issues, Discovery Bay (DB) and the Stockton Channel (STK). Both sites showed the highest proportion of cyanobacteria in the total phytoplankton community biomass during summer months, and this was particularly noticeable at STK. In June 2022, additions of N and N+P were both shown to increase overall phytoplankton biomass in DB and N+P specifically stimulated cyanobacteria. P alone was not stimulatory. In September 2022, NH4 promoted the growth of cyanobacteria faster than NO3, particularly in DB communities. A similar set of responses to N occurred in 2023 in DB, despite major differences in freshwater input between years. In 2022, nutrient additions had no significant stimulatory effects on STK phytoplankton communities, suggesting nutrients were replete throughout the bloom season. However, in 2023 N limitation became more evident in STK, likely due to a dilution effect from the very high freshwater discharge from a record snowpack and reservoir releases, ultimately changing the availability of inorganic N during the CyanoHAB growth period. The combined effect of high flow and nutrient dilution in 2023 was responsible for the reduced CyanoHAB potential. By examining these key differences between seasons in these hydrologically contrasting years, it appears that internal supplies of “legacy P” ensure P availability throughout the summer bloom season regardless of hydrologic variability, while N enrichment plays a key role in stimulating algal production and CyanoHABs under hydrologically variable conditions. Once N was added, P further stimulated biomass production in some cases, indicating potential N+P co-limitation. We conclude that under varying hydrologic conditions, long-term dual N and P input reductions are needed to control eutrophication and CyanoHAB outbreaks throughout the SFBD.

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 HABs and diatoms, in Lake Erie.

Recent work has demonstrated the primary aerosolization of cyanobacterial cells, toxins, and metabolites from cyanobacterial harmful algal blooms (CHABs). However, another possible source of CHAB-derived aerosols is secondary organic aerosol (SOA) formation via the atmospheric oxidation of volatile organic compounds (VOCs) emitted by CHABs. To examine potential SOA formation from CHABs, two cyanobacterial VOCs--2-methylisoborneol (2-MIB) and geosmin (GSM)-- were oxidized via hydroxyl radicals (center dot OH) in a potential aerosol mass-oxidation flow reactor. At 100 ppbv, SOA mass yields were 15.1 +/- 2% and 33.9 +/- 1.3%, from 2-MIB and GSM, respectively. SOA mass concentrations generated from 2-MIB and GSM oxidations reached up to 102 +/- 22 mu g m(-3) and 252 +/- 52 mu g m(-3), respectively, when exposed to 8-16 days of equivalent center dot OH exposure. Offline molecular-level characterization of Teflon-filter collected SOA by reverse-phase liquid chromatography interfaced to high-resolution quadrupole time-of-flight mass spectrometry equipped with electrospray ionization (RPLC/ESI-HR-QTOFMS) revealed 7 distinct chemical compounds in both 2-MIB and GSM-derived SOA, which we propose for use as molecular tracers of CHAB-derived SOA in ambient fine particulate matter (PM2.5). Two 2-MIB-derived SOA tracers (molecular formulas of C10H18O4 and C10H16O5) were measured in PM2.5 collected from the airshed of a CHAB. To the best of our knowledge, this is the first observation of respirable CHAB-derived SOA. Our findings strengthen the need to consider outcomes related to human respiratory health in risk assessments and public health messaging surrounding residential and recreational exposures to CHABs.

Cyanobacterial harmful algal blooms (CHABs) have become a persistent seasonal problem in the upper San Francisco Estuary, California also known as the Sacramento-San Joaquin Delta (Delta). The Delta is comprised of a complex network of open water bodies, channels, and sloughs. The terminus of the Stockton Channel is an area identified as a CHAB “hotspot.” As CHABs increase in severity, there is an urgent need to better understand CHAB drivers to identify and implement mitigation measures that can be used in an estuarine complex like the Delta. We investigated water quality conditions and nutrient dynamics in the Stockton Channel by measuring nutrients in the water column, sediments, and pore waters. In situ nutrient addition bioassay experiments were used to assess the effects of nutrient enrichment on total algal/cyanobacterial growth and pigment concentrations. In both June and September, relative to unamended controls, total chlorophyll and cyanobacterial pigment concentrations were unaffected by nutrient additions; hence, the study area showed signs of classical hypereutrophication, with ambient nitrogen and phosphorus present in excess of algal growth requirements. A cyanobacterial bloom, dominated by Microcystis spp. was present throughout the study area but was most severe and persistent at the shallowest site at the channel terminus. At this site, Microcystis spp. created water quality conditions that allowed for a prolonged bloom from June through September. While targeted nutrient reductions are recommended for long term mitigation, on a shorter timescale, our findings suggest that physical/mechanical controls are the more promising alternative approaches to reduce the severity of CHABs in the terminus of the Stockton Channel.

In addition to obvious negative effects on water quality in eutrophic aquatic ecosystems, recent work suggests that cyanobacterial harmful algal blooms (CHABs) also impact air quality via emissions carrying cyanobacterial cells and cyanotoxins. However, the environmental controls on CHAB-derived aerosol and its potential public health impacts remain largely unknown. Accordingly, the aims of this study were to 1) investigate the occurrence of microcystins (MC) and putatively toxic cyanobacterial communities in particulate matter ≤ 2.5 μm in diameter (PM2.5), 2) elucidate environmental conditions promoting their aerosolization, and 3) identify associations between CHABs and PM2.5 concentrations in the airshed of the Chowan River-Albemarle Sound, an oligohaline, eutrophic estuary in eastern North Carolina, USA. In summer 2020, during peak CHAB season, continuous PM2.5 samples and interval water samples were collected at two distinctive sites for targeted analyses of cyanobacterial community composition and MC concentration. Supporting air and water quality measurements were made in parallel to contextualize findings and permit statistical analyses of environmental factors driving changes in CHAB-derived aerosol. MC concentrations were low throughout the study, but a CHAB dominated by Dolichospermum occurred from late June to early August. Several aquatic CHAB genera recovered from Chowan River surface water were identified in PM2.5 during multiple time points, including Anabaena, Aphanizomenon, Dolichospermum, Microcystis, and Pseudanabaena. Cyanobacterial enrichment in PM2.5 was indistinctive between subspecies, but at one site during the early bloom, we observed the simultaneous enrichment of several cyanobacterial genera in PM2.5. In association with the CHAB, the median PM2.5 mass concentration increased to 8.97 μg m−3 (IQR = 5.15), significantly above the non-bloom background of 5.35 μg m−3 (IQR = 3.70) (W = 1835, p < 0.001). Results underscore the need for highly resolved temporal measurements to conclusively investigate the role that CHABs play in regional air quality and respiratory health risk.

Cyanobacterial harmful algal bloom (CyanoHAB) proliferation is a global problem impacting ecosystem and human health. Western Lake Erie (WLE) typically endures two highly toxic CyanoHABs during summer: a Microcystis spp. bloom in Maumee Bay that extends throughout the western basin, and a Planktothrix spp. bloom in Sandusky Bay. Recently, the USA and Canada agreed to a 40% phosphorus (P) load reduction to lessen the severity of the WLE blooms. To investigate phosphorus and nitrogen (N) limitation of biomass and toxin production in WLE CyanoHABs, we conducted in situ nutrient addition and 40% dilution microcosm bioassays in June and August 2019. During the June Sandusky Bay bloom, biomass production as well as hepatotoxic microcystin and neurotoxic anatoxin production were N and P co-limited with microcystin production becoming nutrient deplete under 40% dilution. During August, the Maumee Bay bloom produced microcystin under nutrient repletion with slight induced P limitation under 40% dilution, and the Sandusky Bay bloom produced anatoxin under N limitation in both dilution treatments. The results demonstrate the importance of nutrient limitation effects on microcystin and anatoxin production. To properly combat cyanotoxin and cyanobacterial biomass production in WLE, both N and P reduction efforts should be implemented in its watershed.

The global expansion of harmful cyanobacterial blooms (CyanoHABs) poses an increasing threat to public health. CyanoHABs are characterized by the production of toxic metabolites known as cyanotoxins. Human exposure to cyanotoxins is challenging to forecast, and perhaps the least understood exposure route is via inhalation. While the aerosolization of toxins from marine harmful algal blooms (HABs) has been well documented, the aerosolization of cyanotoxins in freshwater systems remains understudied. In recent years, spray aerosol (SA) produced in the airshed of the Laurentian Great Lakes (United States and Canada) has been characterized, suggesting that freshwater systems may impact atmospheric aerosol loading more than previously understood. Therefore, further investigation regarding the impact of CyanoHABs on human respiratory health is warranted. This review examines current research on the incorporation of cyanobacterial cells and cyanotoxins into SA of aquatic ecosystems which experience HABs. We present an overview of cyanotoxin fate in the environment, biological incorporation into SA, existing data on cyanotoxins in SA, relevant collection methods, and adverse health outcomes associated with cyanotoxin inhalation.

The global expansion of harmful cyanobacterial blooms (CyanoHABs) poses an increasing threat to public health. CyanoHABs are characterized by the production of toxic metabolites known as cyanotoxins. Human exposure to cyanotoxins is challenging to forecast, and perhaps the least understood exposure route is via inhalation. While the aerosolization of toxins from marine harmful algal blooms (HABs) has been well documented, the aerosolization of cyanotoxins in freshwater systems remains understudied. In recent years, spray aerosol (SA) produced in the airshed of the Laurentian Great Lakes (United States and Canada) has been characterized, suggesting that freshwater systems may impact atmospheric aerosol loading more than previously understood. Therefore, further investigation regarding the impact of CyanoHABs on human respiratory health is warranted. This review examines current research on the incorporation of cyanobacterial cells and cyanotoxins into SA of aquatic ecosystems which experience HABs. We present an overview of cyanotoxin fate in the environment, biological incorporation into SA, existing data on cyanotoxins in SA, relevant collection methods, and adverse health outcomes associated with cyanotoxin inhalation.