Contributed Session.
Lead Organizer: Remington Poulin, University of North Carolina Wilmington (poulinr@uncw.edu)
Co-organizers:
Bianca Rodríguez-Cardona, International Institute of Tropical Forestry (rodriguez.cardona.bm@gmail.com)
Presentations
02:30 PM
Exploring Important Design Parameters for Ozone Nanobubble Technology (NBOT) Treatment for Harmful Algal Blooms (HABs) (9555)
Primary Presenter: Haley Kuhn, The Ohio State University (kuhn.701@osu.edu)
Harmful algal blooms (HABs) are large accumulations of toxin-producing algae that have become more prevalent worldwide. Currently, the widespread treatments for HABs often have negative impacts on water ecology. An alternative approach to HAB treatment, ozone nanobubble technology (NBOT), was investigated in this study. Ozone is a powerful oxidant that reacts with HABs through direct oxidation or through the generation of highly reactive hydroxyl radicals. Nanobubbles are microscopic bubbles with a long lifetime in aqueous solutions and large specific surface area due to their small size. By delivering ozone through the generation of nanobubbles, the effectiveness of ozone treatment may be improved by providing higher mass transfer and increased contact time with contaminants. This study investigated the use of NBOT for HAB treatment by analyzing the immediate effects of ozone nanobubble generation on organic matter, toxins, and nutrients. Samples from the influent, untreated water were compared to samples from the effluent solution immediately following single-pass treatment through the NBOT unit during mesocosm and lake field trials. Results found that NBOT increased DOC while decreasing aromaticity, increased total and aqueous microcystins, and decreased chlorophyll and total nitrogen at high ozone-to-DOC ratios. This study indicates that NBOT may be a viable option for HAB treatment, but a high ozone-to-DOC ratio (>1) is needed.
02:45 PM
TRANSFER OF HARMFUL ALGAL TOXINS FROM GRAZERS TO PREDATORS (8955)
Primary Presenter: Jessica Beyer, University of Oklahoma (beyer@ou.edu)
As harmful algal blooms become more common and intense, the production of cyanotoxins, like microcystins, becomes more problematic. These toxins unequivocally impact aquatic ecosystems, but there is no current consensus on if or how these toxins are transferred through food webs. We used an experimental aquatic ecosystem including Microcystis, the herbivorous zooplankter, Daphnia pulex, and predatory Enallagma damselfly larvae, to test the hypothesis that microcystin would be transferred across trophic levels. We then examined the mechanism for this transfer, testing for the relative contribution of microcystin transferred from Daphnia gut contents versus microcystin in Daphnia tissue. Then we estimated the efficiency of toxin transfer between Daphnia and Enallagma. Overall, we found that microcystin was transferred across trophic levels in this system, but concentrations decreased with increasing trophic level, a process known as biodilution. Nearly all the toxin transferred from Daphnia to Enallagma came not from Daphnia gut contents, but from Daphnia tissue. A surprisingly high fraction of microcystin consumed by Enallagma in the form of microcystin-contaminated Daphnia was incorporated into the tissue of Enallagma. Together, these results demonstrate that the transfer of toxins serves as another mechanism through which food webs, both aquatic and terrestrial, may be negatively impacted by harmful algal blooms.
03:00 PM
Alleviation of phytoplankton light limitation by salinity intrusion in a CDOM rich, oligohaline estuary (8766)
Primary Presenter: Mingying Chuo, University of North Carolina at Chapel Hill (mchuo@unc.edu)
Oligohaline zones of estuaries are often subject to harmful algal blooms. The Chowan River-Albemarle Sound is an oligohaline, eutrophic estuary in northeastern North Carolina. In recent summers, toxigenic cyanobacterial blooms have threatened the ecosystem and its value as an important commercial fishery. Typically, salinity is very low (0-2 psu) throughout what is normally a well-mixed water column. However, intrusions of saltier bottom water (4-8 psu) occur episodically during summer and autumn when river flow is low. High concentrations of colored dissolved organic matter greatly reduce light penetration in the water column. With such strong light attenuation, periodic salinity intrusion events that create a shallower mixed layer might be important for alleviating light limitation. In summer 2023, we measured photosynthetic rates under different irradiances to determine the light limitation status of phytoplankton in the Chowan River-Albemarle Sound and investigated the influence of a salinity intrusion event on light limitation. Phytoplankton production was light-limited even in summer when incident solar radiation was high. The salinity intrusion resulted in a 51% decrease in mixed layer depth and a 59% increase in mean water column irradiance within the mixed layer, thereby partially alleviating light limitation. The dominant algal genus changed from dominance by the high-light adapted cyanobacteria, Dolichospermum, during the salinity intrusion to the low-light adapted cyanobacteria, Pseudanabaena, after the salinity intrusion ended. Phytoplankton growth rates following the salinity intrusion were higher than during the salinity intrusion indicating that the effect of reduced light in the absence of salinity intrusion was offset by higher photosynthetic efficiency of the shade-adapted taxa. Understanding these community-level phytoplankton responses to physically-forced changes in light availability will help explain bloom dynamics and increase the predictability of blooms.
03:15 PM
PHYTOPLANKTON COMMUNITY PHENOLOGY AND SPATIAL VARIABILITY WITHIN A HAB-AFFECTED LAKE SUPERIOR ESTUARY (9541)
Primary Presenter: Peter Birschbach, Natural Resources Research Institute at University of MN Duluth (birsc016@d.umn.edu)
In aquatic ecosystems, cyanobacterial harmful algal blooms (cHABs) have become increasingly frequent and are manifesting in unexpected locations. The St. Louis River Estuary (SLRE) of Lake Superior is one such location, with multiple unprecedented cHABs documented since 2021. Thus, we posed several previously unanswered questions: (1) how do spatial differences in phytoplankton abundance and community composition relate to the estuarine water quality gradient; and (2) how does phytoplankton community phenology vary among SLRE locations, only some of which have experienced cHABs? We implemented a high-frequency oversampling approach from fall 2022 through fall 2024 at 8 spatially heterogeneous SLRE stations. We used multi-dimensional ordination to characterize water quality and track phytoplankton community succession and used constrained ordination in conjunction with random forest analysis to examine relationships between phytoplankton and water quality along the SLRE gradient. Findings include: (1) stations in the lower SLRE had high chlorophyll and dissolved inorganic nitrogen (DIN); (2) diazotrophic cyanobacterial taxa dominated 2023 lower SLRE cHABs, despite persistently elevated DIN; (3) phytoplankton biovolume was controlled strongly by bottom-up regulation (eg., nitrate limitation) in the upper SLRE; and (4) phytoplankton succession showed strong weather-driven differences between the winters of 2023 and 2024. Our findings will help project end-users better understand cHAB threats as they work to develop a foundational long-term SLRE monitoring program.
03:30 PM
INVESTIGATING THE UNDERLYING MECHANISMS OF MICROCYSTIN PRODUCTION IN A TEMPERATE, MESO-EUTROPHIC LAKE (9558)
Primary Presenter: Abigail Ross, University of Colorado Boulder (abro8212@colorado.edu)
Harmful algal blooms (HABs), which can contain toxin-producing cyanobacteria, pose a threat to human and environmental health. Conditions that promote HAB formation are characterized reasonably well, but the mechanisms controlling when certain cyanotoxins are produced are poorly constrained. Microcystins, the most common class of cyanotoxin, have many associated human health risks including liver disease and cancer. These toxins are known to contaminate drinking water and impact recreational activities, therefore it is critical to identify drivers of HAB toxicity. Chautauqua Lake (CL) in western New York is heavily used for both recreational and drinking-water purposes, but suffers from seasonal HABs, particularly in the south basin. Here, ultra-high performance liquid chromatography coupled mass spectrometry (UHPLC-MS) is used to quantify microcystin concentration in CL water samples collected in 2022 and 2023. These results are correlated with cyanobacterial DNA, water chemistry, and weather data to analyze spatiotemporal trends in microcystin concentration compared to those environmental variables. In both years, there were higher concentrations of microcystins in CL’s south basin than in the north basin. There is statistically significant interannual variability in microcystin, total nitrogen and ammonia, fluorescent dissolved organic matter (fDOM), and chlorophyll-A concentrations. The findings in this study suggest that those variables could play an important role in microcystin regulation and synthesis in CL and similar meso-eutrophic lakes.
CS09 - Harmful Blooms
Description
Time: 2:30 PM
Date: 28/3/2025
Room: W208