Unveiling the Ecosystem Responses to changes in atmospheric mercury deposition

Recently, a research team led by Professor Shuxiao Wang from the School of Environment at Tsinghua University integrated a comprehensive global natural archive database of mercury (Hg) accumulation with modelled global atmospheric Hg deposition data. This integration revealed how global ecosystems respond to changes in atmospheric Hg input. The findings of this research were published in the National Science Review.

Mercury Pollution: A Global Environmental Issue

Mercury is recognized by the World Health Organization as one of the top ten chemicals of major public health concern due to its high toxicity and strong tendency to bioaccumulate. The primary sources of Hg include anthropogenic activities such as metal smelting and fossil fuel combustion, as well as natural events like volcanic eruptions. Hg released from these activities predominantly exists in a gaseous form, enabling it to be transported over long distances and eventually polluting global terrestrial and marine ecosystems through dry and wet deposition processes. Despite the long history of Hg contamination, there is a scarcity of long-term data on Hg levels in ecosystems, and it remains unclear how ecosystems respond to changes in atmospheric Hg input.

This Study: From Atmosphere to Ecosystem

The research team developed a global natural archive Hg database spanning the period from 1700 to 2012, incorporating Hg accumulation flux data from 221 cores sourced from ice, peat, lake, and marine sediments (Figure 1). The data revealed that Hg flux in these four types of natural archives increased by five to nine times over the three centuries. By comparing this natural archive data with atmospheric Hg deposition data simulated by the GEOS-Chem model, the study illuminated how different ecosystems responded to changes in atmospheric Hg deposition. Results indicated that lake and peat sediments typically exhibited trends similar to those of atmospheric Hg deposition, whereas ice and marine sediments showed less pronounced responses. This finding suggests that current atmospheric Hg emission control policies may be insufficient for recovering plateau glaciers and marine ecosystems from Hg pollution, highlighting the need for more targeted ecosystem recovery strategies.

The spatiotemporal analysis of natural archive mercury (Hg) accumulation revealed distinct trends between developing and developed regions (Figure 2). In developing areas such as East Asia and Africa, Hg accumulation fluxes in lake sediments were increasing due to the combined effects of coal burning, artisanal small-scale gold mining, and industrial development. Conversely, in developed regions like Europe, there had been a significant decline in Hg fluxes in peat and lake sediments since 1950, demonstrating the effectiveness of local environmental policies. However, in North America, another developed region, Hg accumulation fluxes in peat and lake sediments had not significantly decreased. This difference could be attributed to North America's higher reliance on coal compared to Europe during the study period. Thus, this spatiotemporal analysis underscores the role of coal use in contributing to Hg pollution in global ecosystems, particularly within sedimentary compartments.

Prospects and Significance

1. This interdisciplinary study employed methods from physical geography and atmospheric science to connect sedimentary Hg accumulation with atmospheric Hg deposition. This novel approach provides a new way to study ecosystem responses to pollution input changes.
2. The study compiled a global natural archive Hg database covering data from 1700 to 2012 and modelled global atmospheric Hg deposition from 1980 to 2012, providing important datasets that can support future scientific research and policy designs.
3. By comparing Hg accumulation fluxes across various regions and ecosystems, the study identified key hotspots of Hg accumulation. This information is valuable for formulating effective policies aimed at ecosystem recovery from Hg pollution.

The lead author of the study is Dr. Qinqin Chen and the corresponding author is Professor Shuxiao Wang. This work was funded by the National Natural Science Foundation of China (22222604, 42394094, and 42407138), the International Postdoctoral Exchange Fellowship Program (Talent Introduction Program) (YJ20210103), the Shuimu Scholar Fellowship from Tsinghua University (2020SM075), and the Special fund of State Key Joint Laboratory of Environment Simulation and Pollution Control (22L02ESPC).

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