77 - Gold mining in the Peruvian Amazon leads to high levels of mercury deposition in forests and enhanced methylation in aquatic ecosystems

Artisanal and small-scale gold mining (ASGM) activity in the Peruvian Amazon - a biodiversity hotspot - is expanding, leading to large releases of mercury (Hg) to the atmosphere and deforestation. We examined atmospheric transport and the fate of Hg within terrestrial ecosystems to determine whether Hg from ASGM was entering local forest soils and food webs. We then examined how the creation of ASGM-associated ponds impacts methyl Hg (MeHg) production in aquatic ecosystems. We found that Hg deposition into forests was dependent on both proximity to mining and leaf area index. Intact forests near ASGM had the highest ever reported annual Hg fluxes via throughfall and among the highest levels of annual Hg fluxes via all pathways (bulk precipitation, throughfall, litterfall), as well as elevated total Hg and MeHg levels in soils. Due to the high Hg inputs and storage, along with Hg methylation rates similar to those found in temperate forests, we found that resident songbird Hg concentrations in these forests were 2-12 times higher than those in remote forests and sometimes exceeded thresholds known to impact reproductive success. While the fate of Hg within these forests is concerning, these results suggest the importance of forests for sequestering Hg. If the forests are burned or cleared, Hg could enter into nearby aquatic ecosystems. We found that the extent of lake area in heavily mined watersheds has increased by 670% over the past 34 years in association with ASGM activity. Since we found that the proportion of Hg as MeHg was 5-7 times greater in these lakes than in rivers, the level of Hg risk to organisms is compounded by this land cover change. These results raise important questions about the impact of Hg pollution on aquatic and terrestrial ecosystems and for indigenous communities and wildlife that depend on them.

Authors: Jacqueline Gerson, Simon Topp, Natalie Szponar, Angelica Zambrano, Bridget Bergquist, Eben Broadbent, Charles Driscoll ,Gideon Erkenswick Watsa, David Evers, Luis Fernandez, John Gardner, Heileen Hsu-Kim, Giancarlo Inga, Kelsey Lansdale, Melissa Marchese, Ari Martinez, Caroline Moore, William Pan, Miles Silman, Emily Ury, Claudia Vega, Mrinalini Watsa, Xiao Yang, Tamlin Pavelsky, Emily Bernhardt