New USGS Model Uses Dragonflies to Estimate Freshwater Mercury Risk on U.S. Protected Lands

Mercury is a toxic substance that poses serious health risks to fish, wildlife and humans. While it can originate from natural sources, human activities such as mining and coal combustion also release mercury into the environment. This released mercury accumulates as it moves up the food chain, becoming more concentrated in larger animals. This toxin can hamper brain development in the young, impair brain functions and cognition in fully developed brains, and disrupt reproduction.

Monitoring mercury pollution can be time-consuming and costly, especially in remote areas or on protected lands, such as national parks, wildlife refuges and national forests. A major advantage of the new model is its ability to estimate mercury levels in previously untested areas. The model also provides important insights into how mercury exposure risk varies across different landscapes using commonly collected and widely available information about water chemistry and land cover. The model shows that the potential factors influencing mercury methylation - the process by which inorganic mercury is converted into the more toxic organic form by microorganisms - vary across land characteristics as well as water and soil chemistry.

Results from the new model will assist scientists, resource managers and policymakers in evaluating environmental health risks and monitoring trends over time.

Colleen Flanagan Pritz, a National Park Service ecologist and co-author of the study, stated that "the new mercury predictive model will help park managers assess mercury risks in national park freshwater bodies and guide research, monitoring and management decisions for national parks."

Additionally, the model can help identify communities that might be at higher risk of mercury exposure where monitoring data may be lacking, such as many Tribal Nations near protected lands that rely on local fish for food.

"By predicting mercury risk in freshwater ecosystems on or near protected lands, the model can provide decision makers with data to guide water and fish testing efforts and help inform fish consumption advisories that protect the public," said Christopher Kotalik, a USGS research ecologist and the lead author of the study.

The model can be used on protected lands and in remote regions away from urban and industrial mercury sources. This could be particularly useful in providing insights on how land management and restoration, such as controlled burning used for forest management, may alter mercury risk, said Kotalik.

A key value of this model is overcoming previous limitations that confined mercury prediction methods to smaller local or regional scales.

"The national scale of this new model is a significant step forward in providing vital data that can enhance our understanding of mercury pollution by accounting for differences in the drivers of mercury risk across the nation," said Kotalik.

The model was developed by USGS and NPS experts using data from 21,000 dragonfly larvae collected over thirteen years as part of the Dragonfly Mercury Project, a nationwide initiative that collaborates with the public to collect and measure mercury levels in dragonfly larvae in national parks and other protected areas for scientific analysis.

Dragonflies serve as effective indicators of mercury pollution because mercury levels in their tissues reflect environmental concentrations. Their widespread presence in diverse environments nationwide, from desert wetlands to mountain ponds, makes them ideal for this mercury model.

The study titled, "Ecosystem drivers of freshwater mercury bioaccumulation are context-dependent: insights from continental-scale modeling," is just one step toward the final distribution of this new model. The next task for USGS scientists is to create a publicly accessible dashboard where the model's data will be housed.

For more information about USGS mercury research, visit: https://www.usgs.gov/centers/forest-and-rangeland-ecosystem-science-center/science/dragonfly-mercury-project.

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