Modeling the stability and remobilization of mercury in temperate and permafrost soils under climate change with ORCHIDEE-MICT-PEAT-LEAK

Mercury (Hg) progressively accumulates in soils through processes such as vegetation uptake, litterfall, throughfall, and direct deposition. Soils constitute the largest reservoir of Hg, with surface soil stocks estimated at 235 to 1150 Gg. Despite its significance as a toxic neuropollutant, current environmental policies often overlook the remobilization of legacy Hg stocks stored in soils. However, the stability of soils Hg stocks, as well as the pathways and magnitudes of potential remobilization, remain poorly quantified. Due to the strong affinity of Hg for organic carbon (OC), their cycles are tightly coupled. Consequently, changes affecting OC stability have direct implications for soil Hg stocks. This is particularly critical for permafrost soils, which hold substantial amounts of OC and of Hg (72 Gg in the top 0-30 cm) but are highly vulnerable to climate change-driven thawing.

To address this gap, we are extending the ORCHIDEE-MICT-PEAT-LEAK land surface model, which mechanistically represents the production, transport, and transformation of OC in soils and permafrost, by integrating the Hg cycle. The model will be evaluated against observational data, such as regional surface Hg stock maps and vertical soil core profiles.

Once validated, the model will enable quantification of Hg fluxes emitted into the atmosphere or leaching into rivers. Additionally, simulations under various CMIP6 climate change scenarios will assess the stability of soil Hg stocks across temperate and permafrost regions. This work aims to improve understanding of Hg dynamics in a warming climate and inform strategies for managing Hg risks.