The Dragonfly Mercury Project: Citizen Scientists Track Mercury in National Parks

Mercury is a pollutant found all over the world, and a threat to people and ecosystems. Even national parks receive it, from the air, often after it has travelled long distances. In water, some conditions let microbes turn inorganic mercury into an organic form, methylmercury, which builds up through food webs and is a potent nerve poison and hormone disruptor.

The U.S. Geological Survey, the University of Maine and the National Park Service Air Resources Division are working in more than 50 national parks, with citizen scientists collecting the data, to establish dragonfly larvae (nymphs) as "biosentinels" of mercury in aquatic food webs. To check the method and to link mercury in living things with mercury in the environment, the project also records landscape data and water chemistry (mercury, methylmercury, pH, sulfate and dissolved organic carbon) and mercury in sediment. Because it covers so much ground, it also gives a nationwide snapshot of mercury in mostly undeveloped watersheds.

The 34 national parks sampled in 2014, over 2013 mercury wet deposition from the Mercury Deposition Network. The project grew from a 12-park pilot in 2012 to more than 50 parks. USGS.

Citizen science

The project's reach depends on citizen scientists in each park. In 2014, 824 of them gave 3,951 hours. USGS and University of Maine scientists design the study, the sampling protocol and the training; each park provides resource-management or interpretive staff, or a partner such as a local teacher, to coordinate, train and lead the volunteers. They include:

• students, from middle school to university;
• youth volunteers, for example from the NPS Youth Conservation Corps;
• park volunteers and visitors on park programmes;
• Girl Scouts and Boy Scouts;
• teachers in the NPS Teacher-Ranger-Teacher programme;
• interns from the Mosaics in Science programme.

Citizen scientists make it work: the 2014 season in numbers. USGS.

How samples are collected

1. Sampling kits designed to make the work simple for volunteers are prepared in USGS and University of Maine laboratories and shipped to the parks.
2. Park staff lead the volunteers in the field:
3. • water, by the "clean hands, dirty hands" method, in which one person handles only the collection bottle and another does everything else, to avoid contamination;
   • sediment, with mini-corers taking the top 2 centimetres of stream or lake bed, three replicates per water body;
   • dragonfly nymphs, usually from 3 water bodies per park, 20 caught and analysed individually from each;
   • site notes, coordinates and observations.
4. Laboratories analyse the nymphs for total mercury and methylmercury, the water for total mercury, methylmercury, dissolved organic carbon, pH, anions and conductivity, and the sediment for total mercury.

What the 2014 data show

Mean total mercury in dragonfly larvae by park (bars) and by site within each park (dots), 2014, with standard errors. USGS.

Water chemistry, such as pH and dissolved organic carbon, and landscape features, such as geology and land cover, help identify ecosystems sensitive to mercury methylation and at high risk of mercury building up in sentinel species. Repeated sampling at selected sites in Olympic and Acadia National Parks shows how mercury in the larvae varies through the seasons.

Seasonal total mercury in dragonfly larvae at Acadia and Olympic sites, as the difference from each site's annual mean, in parts per billion. USGS.

What next

• Wider coverage. Observations in places such as the arid Southwest, targeted for 2015 sampling, suggest that different sources and processes may drive high mercury in wildlife in different parks.
• Fish. Where parks sample both fish and dragonfly larvae, the project will test how closely mercury in the two is linked.
• Long-term monitoring, to show how ecosystems respond as conditions change, and to build a national educational opportunity that also serves resource management.
• Education research. With the Schoodic Institute at Acadia National Park, researchers study how students evaluate data and think about the scientific process, to get the most educational value for volunteers.
• DNA barcoding. Dragonfly species differ in diet and life history, which can affect mercury results, and immature dragonflies are hard to identify. Matching their DNA to global databases built from easily identified adults tells the species apart.

Sources

• Collin A. Eagles-Smith, Sarah J. Nelson, James J. Willacker, Jr., Colleen M. Flanagan Pritz and David P. Krabbenhoft, Dragonfly Mercury Project—A Citizen Science Driven Approach to Linking Surface-Water Chemistry and Landscape Characteristics to Biosentinels on a National Scale, USGS Fact Sheet 2016–3005, March 2016. https://doi.org/10.3133/fs20163005
• The map, infographic and graphs are taken from the fact sheet's PDF; a photograph of dragonflies credited to a University of Maine author is not reproduced here.
• Words on this page from people and organisations outside the federal government are paraphrased; rewritten in hubnx's own words.