Sampling dragonflies for mercury analysis in Grand Canyon National Park, 2018–2024: A contribution of the Dragonfly Mercury Project
Flanagan Pritz C, Emery C, Johnson BL, Willacker JJ, Kotalik C, Ko K, Bell M, Walters D, Eagles-Smith CA. 2025. Sampling dragonflies for mercury analysis in Grand Canyon National Park, 2018–2024: A contribution of the Dragonfly Mercury Project. Science Report. NPS/SR—2025/283. National Park Service. Fort Collins, Colorado. https://doi.org/10.36967/2310449
The Dragonfly Mercury Project is a collaborative initiative that utilizes dragonfly larvae as biosentinels to monitor mercury concentrations across 180 national parks and other protected lands, including Grand Canyon National Park (GRCA). These indicators serve as surrogates for environmental risk and can indicate where fish consumption could pose health risks through exposure to mercury. From 2018 to 2024, citizen scientists and staff from the National Park Service and U.S. Geological Survey helped collect close to 400 larvae from 25 GRCA sites across nearly 300 river miles, revealing mercury concentrations ranged from 3.0 to 1337 ng/g (parts per billion) dry weight. Results were available for 20 tributary sites. Upon comparing mercury concentrations to an impairment index, 90% of the sites (N = 18) were classified as low or no risk for ecological impairment, though 10% (2 sites) exceeded moderate or severe risk benchmarks (Pete’s Pocket and Buck Farm Canyon, respectively). The data from GRCA tributaries suggests that Hg risk is relatively low compared to the nationwide dataset. A catch-per-unit-effort metric was used to assess sampling difficulty at 10 sites, revealing that Nankoweap Creek would take the longest to sample, while the mainstem site at Colorado River RM204 would take the shortest. Sources of mercury to GRCA likely stem from a combination of atmospheric deposition, upstream discharge from Lake Powell, and other watershed contributions. In addition, food web dynamics, underlying water chemistry, and environmental disturbances (e.g., floods) contribute to mercury mobilization, production, and bioaccumulation. Report findings provide a baseline for connecting ongoing science in the Colorado River watershed, informing management actions, and enhancing public engagement through citizen science.
- Type
- Published Report
- Authors
- Flanagan Pritz, Colleen; Emery, Colleen; Johnson, Branden; Willacker, James; Kotalik, Christopher; Ko, Katherine; Bell, Michael; Walters, David; Eagles-Smith, Collin
- Date of Issue
- 2025-05
- Publisher
- National Park Service
- DOI
- 10.36967/2310449
- Units
- ARD , GRCA , NRSS
- Keywords
- Atmospheric deposition, Bioaccumulation, Biosentinels, Citizen science, Ecological risk, Indigenous youth