Impact of Water-Induced Soil Erosion on the Terrestrial Transport and Atmospheric Emission of Mercury in China

Terrestrial mercury (Hg) transport, induced by water erosion and exacerbated by human activities, constitutes a major disturbance of the natural Hg cycle, but the processes are still not well understood. In this study, we modeled these processes using detailed information on erosion and Hg in soils and found that vast quantities of total Hg (THg) are being removed from land surfaces in China as a result of water erosion, which were estimated at 420 Mg/yr around 2010. This was significantly higher than the 240 Mg/yr mobilized around 1990. The erosion mechanism excavated substantial soil THg, which contributed to enhanced Hg(0) emissions to the atmosphere (4.9 Mg/yr around 2010) and its transport horizontally into streams (310 Mg/yr). Erosion-induced THg transport was driven by the extent of precipitation but was further enhanced or reduced by vegetation cover and land use changes in some regions. Surface air temperature may exacerbate the horizontal THg release into water. Our analyses quantified the processes of erosion-induced THg transport in terrestrial ecosystems, demonstrated its importance, and discussed how this transport is impacted by anthropogenic inputs and legacy THg in soils. We suggest that policy makers should pay more attention to legacy anthropogenic THg sources buried in soil.