The Dragonfly Mercury Project: A National Scale Assessment of Mercury Bioaccumulation and Risk in US National Parks Through a Citizen Science Framework

Abstract:

The Dragonfly Mercury Project (DMP) is a dynamic national scale program coupling scientific efforts to understand mercury pollution risks to protected areas with citizen engagement and education. We conducted a national-scale assessment of mercury (Hg) bioaccumulation in aquatic ecosystems using dragonfly larvae as biosentinels and implemented a carefully designed sampling methodology for citizen scientists to facilitate biological sampling. We assessed variation in dragonfly Hg concentrations across >450 sites spanning 100 US national parks and other protected places and examined intrinsic and extrinsic factors associated with variation in Hg concentrations. Mercury concentrations ranged between 10.4-1,411 ng/g across sites and varied among habitat types. Dragonfly Hg concentrations were up to 1.8-fold higher in lotic habitats than in lentic habitats, and 37% higher in waterbodies with abundant wetlands along their margins than those without wetlands. Mercury concentrations in dragonflies differed among families, but were correlated with each other, enabling adjustment to a consistent family to facilitate spatial comparisons among sampling units. Dragonfly THg concentrations were positively correlated with THg in both fish and amphibians from the same locations, indicating that dragonfly larvae are effective indicators of Hg bioavailability in aquatic food webs. Using the relationships between dragonfly and fish Hg concentrations we developed a series of integrated impairment indices that inform potential risk of Hg exposure to fish, wildlife, and human health. Most sample sites were in the moderate to low risk category, but 12% of sites were at high or severe risk for mercury, potentially causing harm to fish, wildlife, and people who eat those fish and wildlife. The scope and depth of this work stand it up as a potential landmark study on mercury in NPS lands and across the landscape, particularly in light of the citizen science framework under which it was implemented. More information on the Dragonfly Mercury Project can be found at https://wim.usgs.gov/geonarrative/dmp/ and https://www.nps.gov/articles/dragonfly-mercury-project.htm.