Mercury cycling in the U.S. Rocky Mountains: a review of past research and future priorities

Mercury cycles at levels three- to five-fold higher today than the pre-Industrial era, resulting in global contamination of ecosystems. In the western United States (U.S.), mercury mobilization has led to widespread production of methylmercury (MeHg), a potent, bioaccumulating neurotoxin, which has resulted in fish consumption advisories across all states. Mountain regions are particularly sensitive to continued mercury contamination as they receive higher rates of atmospheric deposition, compared to lower elevations, and have aquatic ecosystems on the landscape conducive to MeHg production. In this paper, we focus on the U.S. Rocky Mountain region and synthesize: (1) current knowledge regarding the mercury cycle; (2) impacts of climate change on the mercury cycle connected to hydrology and wildfire; and (3) future research priorities for informing mercury research and regulation. Studies on the interactions between mercury contamination and climate change in mountain ecosystems is still nascent. We use the findings from this synthesis to summarize the following research needs: (1) quantify sources of mercury in wet and dry deposition, as these pathways dictate mercury exposure and toxicity, and are shifting with climate change; (2) investigate MeHg in mountain aquatic ecosystems, which are important pathways of human mercury exposure and provide food resources and habitat to local wildlife; and (3) examine the disproportionate impact of mercury contamination on indigenous communities through community-led research. Although we focus on the Rocky Mountains for this review, the findings are applicable to semi-arid mountain ecosystems globally and must be prioritized to promote the health of ecosystems and people everywhere.