Poster Presentation Society for Freshwater Science 2026 Annual Meeting

Influence of harmful algal blooms on mercury cycling in New York lakes (134149)

Donovan S Vitale 1 , Jacqueline R Gerson 1 , Samantha L Davies 1 , Casey L Iwamoto 1 , Jennifer Bourgue 2 3
  1. Biological and Environmental Engineering, Cornell University, Ithaca, NY, United States
  2. Division of Fish and Wildlife, New York State Dept. of Environmental Conservation, Albany, NY, United States
  3. New York State Water Resources Institute, Cornell University, Ithaca, NY, United States

Mercury (Hg) contamination and harmful algal blooms (HABs) are widespread stressors threatening freshwater environments. Despite extensive research on each stressor individually, the influence of HABs on Hg cycling is poorly understood. This poses a critical knowledge gap, as HABs decrease oxygen availability and increase the flux of labile organic matter to lake sediment, which collectively increase favorable conditions for microbial organisms that can convert inorganic Hg to the potent neurotoxin methylmercury (MeHg). Once produced, MeHg is highly bioavailable and can be bioaccumulated through the food chain, eventually reaching humans via fish consumption from contaminated water bodies. Lakes in central New York represent a promising and imperative study area to assess the influence of HABs on Hg cycling. In 2024, more than 500 HABs were reported across the state1, and over 200 waterbodies were under fish consumption advisories for Hg contamination2. As HABs become more common and severe, determining their role in MeHg production becomes essential for predicting and mitigating future exposure risks. This research asks: How do total Hg and MeHg concentrations in lake water and sediments change before, during, and after HABs?

To study how HABs influence Hg cycling and MeHg production, lake water and sediment samples were collected from 6 lakes in central NY—three with a history of HABs and three without—on a biweekly basis from May through August 2025 and weekly during HAB events. At each site, sediment samples were collected from both the shoreline and the deepest part of the lake, while water samples were collected from the shoreline, surface water at maximum depth, and bottom water at maximum depth. Additional in situ measurements were collected at each sampling location (e.g., dissolved oxygen, pH, specific conductivity, temperature). Samples are being analyzed in the laboratory for total Hg, MeHg, and dissolved organic carbon concentrations. Additionally, phytoplankton composition was assessed via microscopy. I hypothesize that concentrations of MeHg in water and sediment will be elevated during and following HABS compared to pre-bloom conditions, as widespread water column anoxia and increased fluxes of labile organic matter would promote anaerobic microbial production of MeHg.

  1. (1) Redelmeier, R. Harmful algal blooms found in dozens of New York waterbodies so far this summer. https://www.wskg.org/regional-news/2024-08-26/harmful-algal-blooms-found-indozens- of-new-york-waterbodies-so-far-this-summer (2024).
  2. (2) Waterbodies with Advisories. https://www.health.ny.gov/environmental/outdoors/fish/health_advisories/regional/alphabe tical.htm (2024).