Integration of multiple methodologies as an indicator of cyanotoxin occurrence in Owasco Lake, New York

Cyanobacteria harmful algal blooms (cyanoHABs) pose environmental and public health risks in lakes with highly variable cyanobacteria and cyanotoxin distributions. We compared results from 3 independent monitoring programs to characterize spatiotemporal patterns in the stratified, mesotrophic Owasco Lake, one of the Finger Lakes in New York. Biweekly open-water samples collected at multiple depths in 2019 and 2020 were analyzed for phytoplankton community composition, chlorophyll a, cyanotoxins, and cyanotoxin synthetase gene targets. These data were examined alongside shoreline reports and microcystin measurements from 2 public water supply intakes. Open-water cyanobacterial biovolume was generally low but increased sharply during late summer Microcystis-dominated events. Microcystin was the only cyanotoxin detected and occurred infrequently; detections at drinking water intakes coincided with or followed open-water and shoreline bloom reports. The mcyE gene target was detected weeks before microscopy or cyanotoxin analyses indicated cyanoHAB development and persisted later. Relations among cyanobacterial biovolume, chlorophyll a, gene targets, and cyanotoxins were generally weak (the relations explained small proportions of the variability in the response variables), indicating ephemeral bloom dynamics and low overall biomass. Comparison across programs revealed a consistent sequence: early mcyE detection, shoreline bloom reports, open-water increases in cyanobacteria, sparse microcystin detections, and then detections at drinking water intakes. These findings demonstrate how genetic, chemical, and visual approaches can be combined across depths and monitoring entities. Routine genetic analyses in open water may provide early indications of toxigenic potential, support tiered monitoring frameworks, and inform management of recreational and drinking water risks in large lakes.