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
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Abstract
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 2018–2024, 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 ranging 3.0–1337 ng/g (parts per billion) dry weight. Results were available for 20 sites. Upon comparing mercury concentrations to an impairment index, most sites 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). 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.
Suggested Citation
Flanagan Pritz, C., Emery, C., Johnson, B.L., Willacker, J., Kotalik, C.J., Ko, K., Bell, M.A., Walters, D., Eagles-Smith, C., 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, vi, 41 p., https://doi.org/10.36967/2310449.
Study Area
| Publication type | Report |
|---|---|
| Publication Subtype | Federal Government Series |
| Title | Sampling dragonflies for mercury analysis in Grand Canyon National Park, 2018–2024: A contribution of the Dragonfly Mercury Project |
| Series title | Science Report |
| Series number | NPS/SR-2025/283 |
| DOI | 10.36967/2310449 |
| Publication Date | May 01, 2025 |
| Year Published | 2025 |
| Language | English |
| Publisher | National Park Service |
| Contributing office(s) | Forest and Rangeland Ecosystem Science Center |
| Description | vi, 41 p. |
| Country | United States |
| State | Arizona |
| Other Geospatial | Grand Canyon National Park |