Mercury in Dragonfly Larvae at Mount Rainier National Park, 2020

The Dragonfly Mercury Project (DMP) is a national surveillance, monitoring and research program that pairs citizen science and education with scientific work on the risks mercury poses to protected areas. 2020 was Mount Rainier National Park's seventh year in the project. The data are published at doi.org/10.5066/P9TK6NPT; more is on the project website.

Dragonfly Mercury Project sampling locations in Mount Rainier National Park. Map: NPS.

Mercury in 2020

Unless noted, concentrations are converted to their equivalent in the dragonfly family Aeshnidae (Eagles-Smith and others, 2020), so sites can be compared.

Across the three sites sampled in 2020, site means ranged from 76.0 to 194.7 ng/g.

Mean mercury by site (bars) and dragonfly family (points), with the park mean (dashed line) and the 2014–2020 study mean (dotted line). Site, park and study means are Aeshnid-equivalents; family means are geometric means of raw concentrations. Chart: NPS.

Risk to wildlife and people

The Integrated Impairment Index sorts Aeshnid-equivalent mercury into five categories, by how many kinds of animals are estimated to exceed increasingly severe impairment benchmarks for fish, wildlife and human health. Because it considers many taxa, it gives a fuller picture of risk than any single benchmark.

• In 2020, two Mount Rainier sites were low risk and one was moderate risk.
• Across all parks sampled in 2020, 24% of sites were low risk and 51% moderate risk.

Site mean mercury across all parks, colored by the five Integrated Impairment Index categories, with the 2020 Mount Rainier sites labeled and the percentage of sites in all parks with lower mercury than each. Chart: NPS.

Change over time

In 2020, the park's mean dragonfly mercury was similar to 2016 and 2019 and higher than 2014, 2015, 2017 and 2018.

Annual mean mercury (Aeshnid-equivalents, ng/g dry weight ± standard error), 2014–2020. The means come from a model that accounts for differences in the sites sampled each year. Chart: NPS.

How to read this: annual means were estimated with a model that allows for the different sites sampled each year, and a Tukey HSD test identified which years differ. That makes years comparable despite changing sites — but each site's own character strongly affects dragonfly mercury, and accounting for it adds uncertainty, reducing the power to detect trends. Apparent trends should be read with caution.

Public science

The project engages local communities and uses public science to study mercury pollution across the country.

• 3 public participants helped collect dragonflies at the park in 2020, an average of 1.0 per site.
• They contributed about 5.7 hours, averaging 1.9 hours per site.
• 60% of the larvae with field identifications were correctly identified to family.

Average (bars) and total (numbers in bars) public participants (left) and participant hours (right) at the park in 2020; bold lines mark the averages across all parks that took part. Chart: NPS.

Site results, 2020

In this table, mercury values are raw concentrations, not Aeshnid-equivalents.

Sources

Based on "Dragonfly Mercury Project: Mount Rainier National Park 2020 Data Summary," Mount Rainier Science Brief, National Park Service; a work of the United States government in the public domain. Methods: Eagles-Smith and others, 2020, "A national-scale assessment of mercury bioaccumulation in United States national parks using dragonfly larvae as biosentinels through a citizen-science framework," Environ Sci Technol 54(14): 8779–8790.