A National-Scale Assessment of Mercury Bioaccumulation in United States National Parks Using Dragonfly Larvae As Biosentinels through a Citizen-Science Framework

Abstract

We conducted a national-scale assessment of mercury (Hg) bioaccumulation in aquatic ecosystems, using dragonfly larvae as biosentinels, by developing a citizen-science network to facilitate biological sampling. Implementing a carefully designed sampling methodology for citizen scientists, we developed an effective framework for a landscape-level inquiry that might otherwise be resource limited. We assessed the variation in dragonfly Hg concentrations across >450 sites spanning 100 United States National Park Service units and examined intrinsic and extrinsic factors associated with the variation in Hg concentrations. Mercury concentrations ranged between 10.4 and 1411 ng/g dry weight across sites and varied among habitat types. Dragonfly total Hg (THg) 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 (r 2 > 0.80) with each other, enabling adjustment to a consistent family to facilitate spatial comparisons among sampling units. Dragonfly THg concentrations were positively correlated with THg concentrations in both fish and amphibians from the same locations, indicating that dragonfly larvae are effective indicators of Hg bioavailability in aquatic food webs. We used these relationships to develop an integrated impairment index of Hg risk to aquatic ecosytems and found that 12% of site-years exceeded high or severe benchmarks of fish, wildlife, or human health risk. Collectively, this continental-scale study demonstrates the utility of dragonfly larvae for estimating the potential mercury risk to fish and wildlife in aquatic ecosystems and provides a framework for engaging citizen science as a component of landscape Hg monitoring programs.

Long-Term Trends in Regional Wet Mercury Deposition and Lacustrine Mercury Concentrations in Four Lakes in Voyageurs National Park

“…Details of sampling for age-1 yellow perch and dragonfly larvae have been described elsewhere [24,38,39]. In brief, both yellow perch and dragonfly larvae were sampled annually from each lake during spring.…”

“…In brief, both yellow perch and dragonfly larvae were sampled annually from each lake during spring. Because total mercury concentrations (THg) can vary among families [38], we normalized THg in dragonfly larvae to those of a single family (Aeshnidae) following Eagles-Smith et al [38]. This ensures a consistent unit of dragonfly larvae THg for each site year.…”

Shenandoah Watershed Study‐Virginia Trout Stream Sensitivity Study (SWAS‐VTSSS): Stream water quality and hydrologic monitoring data for mid‐Appalachian headwater streams

“…The physical and chemical data (e.g., seasonal temperature and streamflow extremes, pH and acid neutralizing capacity) have informed concurrent assessments of biological metrics such as macroinvertebrate community structure (Jastram et al, 2013), and biological trends such as brook trout young of year abundance (Blum et al, 2018) and fish species diversity (Harmon et al, 2020). Additionally, the acid-base chemistry data have been paired with concurrent analysis of dissolved (i.e., filtered) mercury, another atmospherically distributed contaminant, to investigate the influence of pH on the relationship between dissolved organic carbon quantity and character and stream mercury concentration (Riscassi & Scanlon, 2011) and to evaluate mercury bioaccumulation in dragonfly larvae (Eagles-Smith et al, 2020). Furthermore, data sets have been used to calibrate and validate biogeochemical models to forecast stream chemical conditions.…”

Effect of Body Size on Methylmercury Concentrations in Shoreline Spiders: Implications for Their Use as Sentinels

“…The level of Hg contamination within waterbodies varies across the landscape due to variations in atmospheric deposition of inorganic Hg and the biogeochemical factors that affect the transport and methylation of inorganic Hg to form toxic and bioaccumulative methylmercury (MeHg; Evers et al 2007; Hsu‐Kim et al 2018). One efficient and inexpensive way to monitor Hg contamination of aquatic food webs is to quantify MeHg concentrations in a sentinel organism (Mason et al 2005; Eagles‐Smith et al 2020), defined as an organism that accumulates contaminants in its tissues without significant adverse effects (Beeby 2001). Ideally, sentinel organisms should be widely distributed, found in high abundance in the environment, easy to collect and identify and their tissue concentrations should reflect levels of a contaminant in the environment (Beeby 2001).…”