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Spatially Balanced Surveys Characterizing Potential Hazard from Benthic Cyanotoxins in Four Rivers of the USA – preliminary results, not externally peer-reviewed
Citation:
Nietch, Chris, Nate Smucker, AND J. Lu. Spatially Balanced Surveys Characterizing Potential Hazard from Benthic Cyanotoxins in Four Rivers of the USA – preliminary results, not externally peer-reviewed. 13th US Symposium on Harmful Algae, Cedar Rapids, IA, October 25 - 29, 2026.
Impact/Purpose:
This research effort includes multiple EPA Program Office, Regions, and State partners. An overview of the latest results on methods evaluation and spatial extent surveys characterizing the potential risk posed by harmful benthic cyanobacteria in rivers will be given. This includes the results for four spatially balanced probability surveys completed in 2024 and 2025. Systems assessed included 415 km of the Virgin River, UT; 587 km of the North Fork of the Shenandoah River (NFSR), VA; 85 km (centerline distance) of the Columbia River in the Tri-Cities area of western WA; and 521km of the banks of the Ohio River, near Cincinnati, OH. The benthic biomass sampled in each had unique risk characteristics in terms of the relative abundance of toxigenes and concentrations of different cyanotoxins. Other results include study-specific potential impact probabilities for specific cyanotoxins in benthic biomass for each survey. An overview of the methods used for characterizing relative differences among toxigenes and cyanotoxins across sites and surveys and the evaluation benthic HAB indicator approach will be provided. This research works to inform decisions related to the unique risk management challenges presented by toxin producing benthic cyanobacteria in rivers and streams.
Description:
Toxin producing benthic cyanobacteria in rivers and streams present unique risk characterization and management challenges. To help address these, US EPA set out to evaluate different field sampling and laboratory methods by conducting studies at seven pilot sites in rivers across six states in 2023. The lessons learned were then used to design four spatially balanced probability surveys that were completed in 2024 and 2025. Systems assessed included 415 km of the Virgin River, UT; 587 km of the North Fork of the Shenandoah River (NFSR), VA; 85 km (centerline distance) of the Columbia River in the Tri-Cities area of western WA; and 521 km of the banks of the Ohio River, near Cincinnati, OH. The benthic biomass sampled in each had unique risk characteristics in terms of the relative abundance of toxigenes and concentrations of different cyanotoxins. To demonstrate potential impacts, study-specific levels for dog ingestion of toxins in benthic biomass were used based on extrapolations from water recreation values and assumptions about body weight and potential ingestion rate. The preliminary results suggest that potential impact probabilities for kilometers assessed were 34% from anatoxin in the Virgin River; 25% and 45% from anatoxin and saxitoxin, respectively in the NFSR; 18% and 32% from microcystin and anatoxin, respectively in the Columbia River; and 10%, 34%, and 54% from anatoxin, saxitoxin, and microcystin, respectively in the sections of the Ohio River sampled. Visual assessments of benthic cyanobacteria cover were not reliable indicators of toxin levels in benthic biomass in this study.