While harmful algal blooms (HABs) are prominent occurrences in coastal zones where microplastic concentrations are maximal, the manner in which microplastics may influence food webs and HABs is poorly understood. This study explored how polystyrene microplastics affected copepod grazing of the saxitoxin-synthesizing harmful dinoflagellate, Alexandrium catenella, as well as a non-toxic dinoflagellate, Gymnodinium aureolum. Experiments were performed using multiple densities of microplastics (250 – 10,000 mL–1) of differing sizes (4 and 10 µm), as well as multiple densities of microalgae in microplates. The addition of 10 µm microplastics at densities of 1000 – 10,000 beads mL–1 consistently and significantly reduced grazing on A. catenella while 10,000 beads mL–1 (10 µm diameter) consistently and significantly increased grazing on G. aureolum (p < 0.05 for all). The addition of 4 µm beads (10,000 beads mL–1) did not alter grazing on A. catenella but did mitigate grazing disruption caused by 10 µm beads when offered as a mixture of bead sizes. When A. catenella and G. aureolum were combined, the addition of 10 µm beads led to grazing rates on G. aureolum that were five-fold greater than A. catenella. In contrast, the algal mixture without bead additions yielded enhanced grazing on G. aureolum while grazing on A. catenella was unchanged compared to mono-algal treatments. Microplastics 10 µm and smaller are poorly studied but likely have disproportionate interactions with lower levels of marine food webs. This study highlights potential co-stressor effects of HABs and microplastics on zooplankton grazers which could combine to promote HABs.

Thermally modified oyster shells, which comprise reactive calcium oxide, show great promise as bio-based adsorbents for phosphate removal from wastewater. However, consensus is lacking on the effects of thermal conversion methods (pyrolysis and calcination) and treatment temperature on phosphate removal performance. Accordingly, thermal conversion methods and temperatures were first screened to identify the optimal material, followed by response surface methodology (RSM) optimization of removal conditions. Screening results showed that pyrolysis and calcination had comparable effects, while only oyster shell treated at 900 degrees C sustained removal efficiencies above 90% at an L/S of 10000, highlighting temperature as the dominant factor. RSM optimization further showed that the calcined oyster shell at 900 degrees C achieved an adsorption amount of 304 mg P/g with 95% removal efficiency at an L/S of 16000. Thus, only 63 g of calcined oyster shell is required to treat 1 m3 wastewater containing 20 mg P/L within one day. XRD, FTIR, and thermodynamic analyses indicated that phosphate removal was primarily through precipitation as calcium hydroxyapatite. Compared to other shellbased adsorbents, calcined oyster shell at 900 degrees C in this study exhibits superior phosphate removal performance, providing theoretical support and practical insights for wastewater treatment.

IntroductionCarbon dioxide removal (CDR) is a necessary component of limiting global warming to 2 °C by 2,100. Marine enhanced rock weathering (mERW) with minerals like olivine is a CDR strategy with the potential to capture atmospheric carbon dioxide and mitigate ocean acidification, which threatens calcifying organisms including those essential for global aquaculture such as oysters. mERW could benefit these species through the local addition of alkalinity, although olivine also releases trace metals like nickel which may bioaccumulate.MethodsThis study presents findings from the world’s first field trial of mERW conducted in New York, USA. Olivine sand was applied to an intertidal beach, where juvenile oysters were exposed over a one-year period. Oyster biomass and trace metal accumulation were subsequently assessed.ResultsOn short (2 month) timescales, Eastern oysters exposed to olivine demonstrated a positive, but non-significant, increase in biomass as compared to control treatments. After a year of exposure, there was no significant difference in oyster biomass or mean metal accumulations between olivine and control treatments (mean for all treatments 2.18 ± 2.71 μg g dw−1 for Ni; <1 μg g dw−1 for Cr and Co).DiscussionMetals concentrations were below US Food and Drug Administration warning thresholds and within global natural ranges. Our findings suggest that mERW with olivine has a limited effect on oysters and that olivine-derived metals did not result in oyster safety concerns for human health.

While harmful algal blooms (HABs) caused by the obligate-mixotroph, Dinophysis acuminata, have been associated with the ciliate, Mesodinium rubrum, the role of zooplankton grazing in the occurrence of these HABs has been under studied. Here, the dynamics of D. acuminata blooms were tracked within two NY, USA, harbors, over three years (2019-2021) during which grazing by native protozooplankton and introduced copepods (Acartia tonsa) was evaluated experimentally using an Imaging FlowCytobot (IFCB) to quantify plankton between 20 µm and 150µm. During each year, protoozooplankton grazing on Dinophysis was low during the bloom initiation period but exceeded cellular growth rates of Dinophysis during the peak bloom period, suggesting that a lack of grazing permitted bloom initiation but grazing onset facilitated bloom decline. The addition of juvenile Acartia increased Dinophysis growth rates in 10 of 14 experiments with differences being significant during three, bloom peak experiments. This finding suggests juvenile copepods can trigger a trophic cascade, potentially consuming Dinophysis-predators and releasing this HAB from grazer control. In contrast, adult Acartia and other mesozooplankton had minimal effects on Dinophysis densities suggesting that mesozooplankton did not directly impact blooms. Collectively, this study demonstrates that reduced grazing pressure at the onset of blooms facilitates bloom development, enhanced grazing during bloom peak can facilitate bloom decline, and that juvenile copepods can promote blooms via the induction of a trophic cascade.

Filter feeding bivalves exposed to the harmful algal bloom (HAB) genus, Dinophysis, become intoxicated by the uptake of diarrhetic shellfish toxins (DSTs) produced by these phytoplankton. Here, three species of bivalve (Crassostrea virginica, Mercenaria mercenaria, and Mytilus edulis) native to the western North Atlantic were exposed to two North American strains of toxigenic Dinophysis acuminata to assess the impacts of cell density, cell density as a fraction of the total plankton community, and differing Dinophysis prey (i.e. strains of the ciliate, Mesodinium rubrum) on bivalve clearance rates. All bivalves cleared D. acuminata faster when the dinoflagellate was offered at moderate densities (10,000 cells L-1) as compared to high densities (100,000 cells L-1). C. virginica cleared a more toxic Massachusetts strain of D. acuminata significantly faster than a less toxic New York strain (p < 0.05). When presented with Dinophysis in mixed culture with the non-HAB species, Rhodomonas salina, in varying proportions, C. virginica clearance rates slowed significantly as the relative and absolute abundance of D. acuminata increased (p < 0.05), whereas M. edulis displayed a preference for the algae that was more abundant. While C. virginica and M. edulis cleared R. salina significantly faster than M. mercenaria (p < 0.05), there were no differences in the clearance rates of D. acuminata among bivalves. In an additional experiment where M. edulis was exposed to a constant, density (similar to 15,000 cells L-1) of D. acuminata for 36 h and then fed a non-toxic food source for 24 h to quantify toxin accumulation and depuration, mussels rapidly accumulated DSTs and pectenotoxins (PTXs) during exposure to Dinophysis but depurated PTXs at a rate 3-14 times faster than DSTs (p = 0.07). Collectively, this study demonstrates that the accumulation of DSTs in bivalves varies as a function of D. acuminata density, species, and strain, and that feeding characteristics of, and toxin dynamics within, M. edulis make it more vulnerable to DST accumulation than C. virginica and a likely DST vector in bloomprone regions.

Onsite wastewater treatment systems (OWTSs) are designed for the removal of pathogens and nutrients from septic effluent. However, many other contaminants are widespread in wastewater including pharmaceuticals, personal care products, and other trace organic chemicals. We analyzed per/polyfluoroalkyl substances (PFASs) in residential septic effluent and investigated their fate in nitrogen-removing biofilters (NRBs), an innovative and alternative type of OWTS. We measured concentrations of 22 targeted PFASs in septic effluent pre- and post-NRB treatment in nine residential OWTSs. We measured total PFAS in septic effluent ranging from 42 to 9795 ng L-1 and in NRB effluent ranging from 72 to 2575 ng L-1, corresponding to estimated effluent loads of 39 to 1423 mg PFASs per household per year. Perfluoroalkyl carboxylates (PFCAs) were generally enriched in NRB effluent versus influent while perfluoroalkyl sulfonates appeared to be partially removed during NRB treatment. Grab sampling results were highly variable but passive sampling (microporous polyethylene tubing containing WAX sorbent) consistently showed greater PFAS levels post-NRB treatment. High-resolution mass spectrometry screening of composited grab samples using two different workflows (suspect screening and untargeted analysis with ion mobility spectrometry) resulted in tentative identifications of 40 additional PFASs not included on the target list. The average mass defect of features identified as potential PFASs was significantly lower (p = 0.014) in post-NRB samples. This, along with increasing concentrations of PFCAs in effluent, suggested transformation of precursors to end products with greater fluorinated character in the NRB.

Estuaries are dynamic environments that provide vital habitat to ecologically and commercially important bivalves. In some cases, freshwater tributaries can introduce cyanobacteria and associated cyanotoxins into estuaries that may subsequently accumulate in estuarine bivalves. Temporarily open/closed estuaries (TOCEs), which only experience tidal input for limited periods of time, may be particularly vulnerable to the accumulation of cyanotoxins in bivalves as they can be subject to freshwater input without tidal flushing and may experience lower salinities and cyanobacterial blooms. This study quantified levels of microcystin in bivalves collected as a time series over a five-year period (2017-2021) from Mecox Bay, a TOCE on Long Island, NY, USA, that hosts a productive oyster fishery and is downstream of a freshwater body that hosts microcystin-producing cyanobacterial blooms. During the study, microcystin was detected in all bivalves monitored including Eastern oysters (Crassostrea virginica), blue mussels (Mytilus edulis), and soft-shell clams (Mya arenaria), with levels in oysters exceeding those in other species and frequently exceeding 10 ng g-1, the California regulatory action level for microcystin in tissue. While oysters were capable of depurating 60-90 % of microcystin after four-to-six weeks during summer, microcystin loads in bivalves often peaked in cooler months after water column cyanobacteria and microcystin levels had seasonally declined, suggesting toxin depuration slowed at colder temperatures. Multiple linear regression models established that time-integrated measurements of pelagic microcystin concentrations in freshwater and estuarine locations, water temperature (inverse correlation), and salinity had highly significant (r2 = 0.71; p < 0.001) predictive power of the microcystin content in oysters. These findings demonstrate that bivalves, particularly oysters, in TOCEs located downstream of microcystin-producing cyanobacterial blooms are vulnerable to microcystin contamination, especially during fall months when temperature-dependent toxin depuration rates are likely slow.

Estuaries are dynamic ecosystems that are an important habitat for bivalves. The freshwater bodies that discharge into estuaries can introduce cyanobacteria and cyanotoxins that may accumulate within food webs. Microcystin is a hepatotoxin that causes adverse health effects in humans and can be harmful to terrestrial and aquatic organisms. Microcystin has been detected in marine bivalves and the rate of microcystin accumulation and depuration differs between bivalve species. No study has explored the presence or dynamics of microcystins in bivalves in the Northeast US, where they represent a major fishery. This study quantified levels of microcystins in wild and cultured bivalves as a time series from 2017 to 2021 in three of the largest US East Coast estuaries (Chesapeake Bay, the Hudson River Estuary, and Long Island Sound) that have hosted microcystin-producing cyanobacterial harmful algal blooms (CHABs) within their watersheds. During this study, microcystins were rarely detected in bivalves across Chesapeake Bay but were commonly quantified in multiple bivalve species in the Hudson River estuary and within two harbors of Long Island Sound, Stony Brook Harbor and Conscience Bay. Microcystins were detected in clams (Mercenaria mercenaria and Corbicula fluminea), Eastern oysters (Crassostrea virginica), and mussels (Mytilus edulis and Geukensia demissa). Eastern oysters (C. virginica) had significantly higher levels of microcystin than other bivalve species (p < 0.05) and often contained microcystin even when other bivalves sampled concurrently did not, suggesting oysters may be a vector for hepatotoxic shellfish poisoning in estuaries. Microcystins were detected in oysters even in fall months after water column cyanobacterial biomass and microcystins had decreased to low levels, suggesting toxin depuration slows during colder months. Collectively, this study demonstrates that microcystin accumulation in estuarine bivalves, particularly Eastern oysters (C. virginica), occurs within several of the larger US East Coast estuaries and could represent a public health risk.

Hydrogen peroxide (H2O2) has been used to mitigate cyanobacterial harmful algal blooms (CHABs), yet little is known about how H2O2 affects specific CHAB-forming genera as well as cyanotoxins beyond microcystin. This project examined the dose-dependent effects of H2O2 on six strains of Dolichospermum spp. including those that produce saxitoxin, anatoxin-a, and microcystin. Beyond toxins, this study quantified changes in photosynthetic efficiency, cell density, H2O2 concentration, and N2-fixation rates. All strains were sensitive to H2O2 with responses being dependent on dose (0-30 mg L-1) of H2O2, cell density, and strain. At 1 × 105 cells mL-1, 4 mg H2O2 L-1 significantly reduced cell density, photosynthetic efficiency, toxins, and N2-fixation rates of all strains (p < 0.05 for all compared to controls). At 1 × 106 cells mL-1, however, higher doses of H2O2 were needed to reduce one or more of the variables, with some strains unaffected by as much as 15 mg L-1, a concentration known to harm zooplankton and invertebrates. While H2O2 degraded anatoxin-a at all cell densities and doses, at 1 × 106 cells mL-1 neither microcystin nor saxitoxin were significantly degraded after four days, even by 15 mg H2O2 L-1, despite significant reduction in Dolichospermum cell densities. This finding suggests that during dense Dolichospermum blooms, H2O2 treatment may destroy cells but may concurrently liberate saxitoxin or microcystin that persists in the water column and enters food webs. Collectively, this study demonstrated that although H2O2 can efficiently lyse Dolichospermum cells, doses needed to mitigate dense blooms of all strain types (≥15 mg L-1) may harm non-target organisms and may not effectively degrade saxitoxin and microcystin.

The accurate evaluation of denitrification rate and greenhouse gas (GHG) emission in field-scale woodchip bioreactors for onsite wastewater treatment are problematic due to inevitably varied environmental conditions and underestimated GHG production with limited analysis of dissolved gas in field samples. To address these problems, batch incubation experiments were conducted with controlled conditions to precisely evaluate the denitrification kinetics and N2O and CH4 emission of both gaseous and dissolved phases in fresh (6 months) and aged (5 years) woodchip bioreactors treating onsite wastewater at high (1-3 mg L-1) and no (0 mg L-1) dissolved oxygen (DO) levels. NO3- removal rate decreased from 37.5-119.0 g NO3--N m-3d-1 at no DO to 8.8-16.6 g NO3--N m-3d-1 at high DO (1-3 mg L-1) due to the growth suppression of NO2- reducing microorganisms (37-55 % lower nirS+nirK abundance). However, the presence of high DO increased N2O emission level from 5.6-6.9 mg N2ON m-3 at no DO to 179.5-273.6 mg N2ON m-3) due to the enhanced growth of NO reducing microorganisms (1-7 times higher norB levels) and the decreased abundance of N2O reducing microorganisms (53-75 % lower nosZ abundance). On the other hand, increased DO level negatively correlated with CH4 production (1.0-3.9 g CH4-C m-3d-1) in fresh woodchips, while showed insignificant impact on CH4 production (0.1-1.4 g CH4-C m-3d-1) in aged woodchips. Woodchip age increase (5 years) negatively impacted the NO3- removal rate (75-85 % lower than fresh woodchips) and CH4 production rate (>3 times lower than fresh woodchips), probably due to the reduced biomass density of NO2- reducing microorganisms (52-58 % lower nirS+nirK abundance) and methanogens (95-98 % lower mcrA levels). The incubation results suggested that long hydraulic retention time (>2-5 days) and anaerobic/anoxic condition are preferred for the optimal NO3- removal and low N2O emission potential of woodchip bioreactors treating onsite wastewater.

Alexandrium pacificum, a globally distributed dinoflagellate, is well-known for causing harmful algal blooms and producing Paralytic Shellfish Toxins (PSTs), a threat to marine life and human health. The frequency and intensity of Alexandrium blooms have increased in recent decades, driven, in some cases, by increasing temperatures. Here, we investigated the temperature-dependent (15 °C, 20 °C, 25 °C, and 30 °C) growth rates and paralytic shellfish toxin profiles of eight A. pacificum strains while concurrently examining differences in sequences of the saxitoxin biosynthetic gene, sxtA4. While maximum cell densities were lowest at 30 °C, toxin production per cell was highest at higher temperatures that inhibited growth, with greater diversity of toxin analogs peaking at 30 °C, as confirmed by the higher Shannon’s diversity index obtained for the toxin profiles with the increasing temperatures. Furthermore, genetic analysis of the sxtA4 gene showed that greater genetic diversity—quantified by nucleotide diversity (π) ranging from 9.91 to 30.21 across strains—was positively correlated with this wider array of toxin analogs (Shannon’s diversity index; p < 0.0001). Conserved regions within the gene were identified, suggesting that these regions may play important structural or functional roles in the saxitoxin biosynthetic pathway. These findings highlight the role of temperature, genetic diversity, and sxtA4 conserved regions in influencing toxin production and profiles in Alexandrium. Further research into the genetic mechanisms underlying saxitoxin biosynthesis will improve our understanding of Alexandrium’s adaptability to changing temperatures. Such insights are essential for effective ecosystem management and safeguarding public health.

1,4-Dioxane is a persistent contaminant that is not effectively removed by conventional water treatment processes. In this study, bench-scale granular activated carbon (GAC)-based biologically active filtration (BAF) systems were developed to metabolically degrade 1,4-dioxane at environmentally relevant levels (<1000 μg L-1). BAF was established using predeveloped biologically activated carbon particles by mixing a 1,4-dioxane-degrading microbial community with granular activated carbon. 1,4-Dioxane removal performance was examined at a range of 1,4-dioxane concentrations (100-1000 μg L-1), hydraulic loading rates (3.6-14 cm h-1), and with the presence of co-contaminants (natural organic matter (NOM) and 1,1-DCE). BAFs achieved 69 ± 7 % removal with an influent 1,4-dioxane concentration of 100 μg L-1 and hydraulic loading rates of 3.6-14 cm h-1, with the lowest effluent concentration of 21 μg L-1. The presence of NOM and 1,1-DCE negatively and irreversibly impacted 1,4-dioxane removal performance of BAF, and pretreatment processes to remove co-contaminants are crucial to maintain the 1,4-dioxane removal efficiency. Microbial analysis revealed the enrichment of 1,4-dioxane degrading species (CB1190-like bacteria) and functional genes responsible for 1,4-dioxane biodegradation (dxmB and aldh) at the top 12 cm of the columns, suggesting the effectiveness of biological 1,4-dioxane removal within short column lengths. This study demonstrated effective metabolic 1,4-dioxane removal at environmentally relevant concentrations by the BAFs, and can provide insights into designing better 1,4-dioxane remediation strategies.

Per- and polyfluoroalkyl substances (PFAS) are persistent organic pollutants in estuaries. In this study, 19 PFAS were quantified in surface waters, sediments, marine invertebrates (aquatic worms, Eastern oysters, and blue crab), and forage fish (Atlantic silverside, four-spine stickleback, mummichog, sheepshead minnow, and rainwater killifish) in an aqueous film forming foam (AFFF)-contaminated estuary, Georgica Pond (NY, USA). Carbon and nitrogen stable isotopes (δ13C and δ15N) were used to determine trophic position of organisms and to identify modes of PFAS exposure. The influence of salinity (8 to 26 practical salinity units, PSU) on the relative and absolute abundance of PFAS in all matrices was also investigated. Eleven long- and short-chain perfluoroalkyl acids (PFAAs) were found to have bioaccumulation potential (bioaccumulation factor, BAF; biota-sediment accumulation factor, BSAF) and were positively correlated with relative trophic position. Among these, long-chain PFAAs (perfluorohexanesulfonic acid, PFHxS; perfluorooctane sulfonic acid, PFOS; perfluorooctanoic acid, PFOA; perfluorononanoic acid, PFNA) were the greatest contributors to total body burden and bioaccumulated in all organisms, with PFOS (log BAF = 3.55 ± 0.83) and PFNA (log BAF = 3.17 ± 0.46) having the highest mean values of all compounds. PFOS was present in all biota samples and concentrations significantly increased with food web trophic position (ranging from 0.18 to 777 μg kg-1). Perfluorobutane sulfonic acid (PFBS) was also ubiquitous among all organisms, bioaccumulating in both invertebrate and vertebrate species. Total PFAS concentrations in aquatic worms were significantly higher in lower salinity water while the PFAS profile of Eastern oysters shifted from predominately perfluorocarboxylic acids (66 % of total composition) to perfluorosulfonic acids (62 %) as the ecosystem transitioned from low (9 PSU) to high (25 PSU) salinity. Collectively, this study demonstrates the utility of applying δ13C and δ15N to determine bioaccumulation patterns of both legacy PFAS and short-chain replacement compounds and underscores how shifts in salinity can alter the concentration and speciation of PFAS in estuaries.

Pseudo‐nitzschia is a genus of harmful algal bloom (HAB)‐forming diatoms that can produce domoic acid (DA), a compound known to cause death and disease in marine wildlife as well as amnesic shellfish poisoning in humans. Here, we show the effects of multiple cultivable seaweeds— Saccharina latissima (sugar kelp), Ulva spp., and Gracilaria spp.—on multiple toxic species of Pseudo‐nitzschia . Co‐culture growth assays of Pseudo‐nitzschia multiseries and Pseudo‐nitzschia australis together with environmentally realistic concentrations of each seaweed showed that all seaweeds except for Gracilaria caused significant reduction in Pseudo‐nitzschia cell density relative to control treatments of 13%–47% in 24‐to‐48 h and up to 74%–94% reduction at 72 h and later ( p < 0.05 for all assays). In almost all experiments, Pseudo‐nitzschia spp. in control treatments displayed exponential growth whereas populations in seaweed treatments did not. Bottle incubations of field‐collected bloom populations of Pseudo‐nitzschia spp. containing different Pseudo‐nitzschia species assemblies with aquaculture realistic concentrations of S. latissima led to a significant reduction in Pseudo‐nitzschia spp. cell density of 69%–81% by S. latissima at 2 g L −1 ( p < 0.05 for all assays). In toxin accumulation experiments, S. latissima significantly lessened ( p < 0.05) DA accumulation in blue mussels ( Mytilus edilus ) and razor clams ( Ensis leei ). Collectively, these results suggest that the integration of seaweeds (particularly S. latissima ) with shellfish aquaculture should be considered as a non‐invasive and potentially profit‐generating measure to mitigate the damage to that industry caused by the growing threat of Pseudo‐nitzschia blooms.

Cyanobacterial harmful algal blooms (CHABs) are promoted by excessive nutrient loading and, while fertilizers and sewage are the most prevalent external nutrient sources in most watersheds, the differential effects of these nutrient sources on CHABs are unknown. Here, we tracked CHABs and performed experiments in five distinct lakes across the Northern US including Lake Erie. Fertilizers with ammonium and orthophosphate, membrane (0.2 μm)-filtered sewage (dominated by reduced forms of nitrogen) sand-and membrane-filtered sewage (dominated by nitrate), and an inorganic nutrient solution of ammonium and orthophosphate were used as experimental nutrient sources for CHABs at N-equivalent, environmentally realistic concentrations. Phytoplankton communities were evaluated fluorometrically, microscopically, and via high throughput sequencing of the 16S rRNA gene, and levels of microcystin and the δ15N content of particulate organic nitrogen (δPO15N) were quantified. Fertilizer and both sources of wastewater increased the abundance of cyanobacteria in all experiments across all five lakes (p < 0.05 for all) whereas effects on eukaryotic phytoplankton were limited. Sand-filtered sewage contained less P, organic matter, and ammonium but more nitrate and had a 25% less potent stimulatory effect on cyanobacteria than membrane-filtered sewage, suggesting nitrification may play a role in reducing CHABs. Fertilizer increased microcystin levels and decreased the δPO15N whereas wastewater increased δPO15N (p < 0.05 for all). Microcystis was the genus most consistently promoted by nutrient sources (p < 0.05 in all experiments), followed by Cyanobium (p < 0.05 in 50% of experiments), with increases in Microcystis biomass consistently elicited by membrane-filtered wastewater. Collectively, results demonstrate that differing types of sewage discharge and fertilizers can promote CHAB intensity and toxicity, while concurrently altering CHAB diversity and δPO15N. While membrane-filtered sewage consistently favored Microcystis, the discharge of sewage through sands muted bloom intensity suggesting sand-beds may represent a tool to remove key nutrients and partially mitigate CHABs.

Dinophysis is an obligate mixotroph that relies on consumption of the ciliate, Mesodinium rubrum, to grow and form harmful algal blooms (HABs). In this study, blooms of Dinophysis acuminata in two NY, USA, estuaries were studied over the course of 3 yr (2019-2021) using discrete samples and an Imaging FlowCytobot (IFCB) to capture images of plankton 20-150 mu m. The darkness of Dinophysis images on the IFCB was used to quantify the "fullness" or feeding state of Dinophysis cells. Culture experiments performed to ground truth this approach revealed a highly significant correlation (R = 0.98; p < 0.001) between the darkness of Dinophysis cells and the abundance of Mesodinium. With a quantitative scale developed to track the fullness of Dinophysis cells, ecosystem observations revealed the percentage of "full" Dinophysis cells increased during blooms of a large-morphotype Mesodinium that preceded the initiation of Dinophysis blooms. A smaller morphotype Mesodinium appeared during Dinophysis bloom peaks suggesting they supported bloom maintenance. While the relative abundance of diatoms was elevated before Dinophysis blooms, other dinoflagellates and tintinnids increased in abundance during these HABs indicating they emerged within a consortium of heterotrophs and mixotrophs that may have collectively filled the same open niche as Dinophysis. This study reveals the manner in which different Mesodinium populations co-bloom with Dinophysis to support plastid acquisition, bloom initiation, and bloom maintenance and contextualizes these changes within the larger plankton community succession associated with these HABs.

Nitrogen-removing biofilters (NRBs) are alternative on-site wastewater treatment systems that can remove some trace organic contaminants (TOrCs) from domestic wastewater, though the dominant removal mechanisms are uncertain. We conducted column experiments representative of the nitrifying sand layer of an NRB to evaluate the contribution of sorption to removal of 16 wastewater-relevant TOrCs. The contribution of sorption was >25% for eight of the 16 TOrCs in at least one experimental treatment and >50% for five TOrCs. Transformation appeared to account for 51-93% of TOrC removal in columns. Transformation product screening resulted in the tentative identification of three TOrC transformation products in column effluent. To compare the bench-scale experiment to realistic field conditions, we analyzed solid samples from a recently excavated full-scale NRB. Median concentrations of sorbed TOrCs ranged from 0.02 to 5.09 ng/g in column studies and 0.05-7.14 ng/g in the full-scale NRB. Overall, the majority of TOrC removal in our laboratory study was by transformation, though some hydrophobic TOrCs exhibited significant removal by sorption. The concentration of sorbed hydrophobic TOrCs in aged NRBs and release of transformation products of frequently detected TOrCs should be taken into consideration during future system design and optimization.

The effectiveness of phosphorus (P) removal by sand filters is limited during septic tank effluent (STE) treatment. The elevated effluent P concentrations pose threats to drinking water quality and contribute to eutrophication. The concern of P leaching from sand filters is further exacerbated by the increased frequency of flooding and natural precipitation due to climate change. This study aimed to understand P attenuation and leaching dynamics, as well as the removal mechanisms in sand filters treating STE, offering insights into the design and implementation of P removal/recovery modules to onsite wastewater treatment systems. P attenuation and leaching during STE treatment and rainfall were studied in bench-scale columns (new vs. aged sand). At standard STE loading (1.2 gallon d−1 ft−2), 24–32% removal of total phosphorus (TP) was achieved, while increased P removal efficiency (35–53%) was observed at low loading (0.6 gallon d−1 ft−2) with influent containing 10.3–20.0 mg P L−1. Complete breakthroughs were observed in both aged (12–70 days) and new columns (27–73 days) at test hydraulic loadings. The maximum TP attenuation level was 20.6–45.3 mg P kg−1 and 25.3–33.0 mg P kg−1, in aged and new sand columns, respectively. When simulated rain was applied (15–60 mm h−1), 80–97% of the attenuated P leached out and the leaching dynamics were impacted by rainfall duration rather than the intensity. The highest concentrations of TP (15.6–15.9 mg L−1) were leached out from both columns within the first 2–6 h. Orthophosphate was the dominant P species in treated effluent (83–84%) and leachate (69–88%), demonstrating its significance as the major P form in the discharge. In addition, aged sand (>5 years) accumulated higher levels of Mg, Al, Ca, and Fe, thus enhancing the P attenuation level during STE treatment. Collectively, this study underscored the importance of frequent field monitoring for reliable long-term P removal estimates.

Cyanobacterial harmful algal blooms (CHABs) are increasingly common in freshwater ecosystems and are often associated with climate change. Here, we used two independent high‐resolution surface temperature records (1995–2022) and temperature‐dependent growth rates of Microcystis to evaluate changes in these CHABs in Lake Erie. The potential mean seasonal growth rate of Microcystis and the duration of the Microcystis bloom season have both significantly increased within the western basin of Lake Erie since 1995. Trends were strongest in the far western region of Lake Erie including Maumee Bay which receives the largest point source of nutrients in the Lake and where the Microcystis bloom season has expanded by up to 1 month. In contrast, warming trends in bloom‐free portions of central and eastern Lake Erie have been more muted. We conclude that increasing water temperature is an important factor facilitating the intensification of these, and likely other, CHABs, and is thus promoting an expanding public health threat.