Global change effects on biogeochemical mercury cycling

Abstract

Past and present anthropogenic mercury (Hg) release to ecosystems causes neurotoxicity and cardiovascular disease in humans with an estimated economic cost of $117 billion USD annually. Humans are primarily exposed to Hg via the consumption of contaminated freshwater and marine fish. The UNEP Minamata Convention on Hg aims to curb Hg release to the environment and is accompanied by global Hg monitoring efforts to track its success. The biogeochemical Hg cycle is a complex cascade of release, dispersal, transformation and bio-uptake processes that link Hg sources to Hg exposure. Global change interacts with the Hg cycle by impacting the physical, biogeochemical and ecological factors that control these processes. In this review we examine how global change such as biome shifts, deforestation, permafrost thaw or ocean stratification will alter Hg cycling and exposure. Based on past declines in Hg release and environmental levels, we expect that future policy impacts should be distinguishable from global change effects at the regional and global scales.

A Spatial Assessment of Current and Future Foliar Hg Uptake Fluxes Across European Forests

“…The impact of the hot and dry conditions on the pine Hg uptake fluxes might have implications for Hg inputs into aquatic ecosystems. In a recent review on Hg cycling in the context of global change Sonke et al (2023) highlighted the potential of legacy Hg (i.e., actively cycling Hg that was mobilized in the past) to cause contamination by mobilization of Hg from soils to wetlands and coastal ecosystems via riverine systems. While most soil Hg enters riverine systems by soil erosion from agricultural lands, contaminated sites, and deforested woodland (Panagos et al, 2021;Sonke et al, 2023), a reduced forest foliar Hg uptake and subsequent deposition to forest soils may decrease the amount of runoff Hg from forest soils in the long-term, while long-range Hg transport to the open ocean via the atmosphere might be enhanced .…”

“…A source of model uncertainty of the future forest foliar Hg uptake flux under climate change arises from atmospheric Hg(0) concentrations that depend on anthropogenic emissions, re-emissions of mobilized legacy Hg and future global deposition fluxes under climate and land use change (Feinberg et al, 2023;Sonke et al, 2023), which we could not account for in this study. However, our model outputs call attention to the sensitivity of the pine needle Hg uptake flux to extreme hot and dry ambient conditions, which should be accounted for in CTMs under varying atmospheric Hg(0) levels.…”

“…Consequently, vegetation uptake has the potential to lower atmospheric Hg(0) transport and Hg deposition to oceans, where Hg can be methylated and bioaccumulated in marine seafood for human consumption (Zhou et al., 2021). In order to assess and improve the effectiveness of mitigation policies for human exposure, it is thus necessary to advance our understanding of environmental drivers of vegetation Hg(0) uptake, particularly in the context of global change (Sonke et al., 2023).…”

“…Global vegetation and soil Hg(0) uptake is estimated at 2,850 ± 500 Mg year −1 and primarily driven by forests (Feinberg et al., 2022; Obrist et al., 2021; Zhou et al., 2021). The amount of forest Hg(0) deposition exceeds approximate direct anthropogenic emissions to the air of 2,200 Mg Hg year −1 (Sonke et al., 2023). In forests, half of the total Hg(0) net deposition is estimated to be stored in tree foliage, while the other half is estimated to be transferred to vascular tissues (e.g., stem, branches, roots), taken up by understory vegetation (e.g., shrubs, grasses) and nonvascular plants (lichen and mosses) or Hg is directly transferred to the forest floor (Obrist et al., 2021; Zhou & Obrist, 2021; Zhou et al., 2021, 2023).…”

Stable Tuna Mercury Concentrations since 1971 Illustrate Marine Inertia and the Need for Strong Emission Reductions under the Minamata Convention

“…11 Anthropogenic Hg uses and emissions have considerably modified the natural global Hg cycle. 12,13 In the atmosphere, higher Hg levels are measured in the northern hemisphere, following the location of the main anthropogenic Hg emissions. 14 In the open ocean, total Hg concentrations at depths of 100−1000 m are thought to have tripled globally, 15 yet scarce Hg observation data in seawater suggest contrasting temporal trends.…”