Abstract
Abstract. Substantial amounts of mercury (Hg) in the terrestrial environment reside in soils and are associated with soil organic carbon (C) pools, where they accumulated due to increased atmospheric deposition resulting from anthropogenic activities. The purpose of this study was to examine potential sensitivity of surface soil Hg pools to global change variables, particularly affected by predicted changes in soil C pools, in the contiguous US. To investigate, we included a soil Hg component in the Community Land Model based on empirical statistical relationships between soil Hg / C ratios and precipitation, latitude, and clay; and subsequently explored the sensitivity of soil C and soil Hg densities (i.e., areal-mass) to climate scenarios in which we altered annual precipitation, carbon dioxide (CO2) concentrations and temperature. Our model simulations showed that current sequestration of Hg in the contiguous US accounted for 15 230 metric tons of Hg in the top 0–40 cm of soils, or for over 300 000 metric tons when extrapolated globally. In the simulations, US soil Hg pools were most sensitive to changes in precipitation because of strong effects on soil C pools, plus a direct effect of precipitation on soil Hg / C ratios. Soil Hg pools were predicted to increase beyond present-day values following an increase in precipitation amounts and decrease following a reduction in precipitation. We found pronounced regional differences in sensitivity of soil Hg to precipitation, which were particularly high along high-precipitation areas along the West and East Coasts. Modelled increases in CO2 concentrations to 700 ppm stimulated soil C and Hg accrual, while increased air temperatures had small negative effects on soil C and Hg densities. The combined effects of increased CO2, increased temperature and increased or decreased precipitation were strongly governed by precipitation and CO2 showing pronounced regional patterns. Based on these results, we conclude that the combination of precipitation and CO2 should be emphasised when assessing how climate-induced changes in soil C may affect sequestration of Hg in soils.
Highlights
Sciences tios and precipitation, latitude, and clay; and subsequently explored the sensitivity of soil C and soil Hg densities to climate scenarios in which we altered annual precipitation, carbon dioxide (CO2) concentrations and temperature.Our model simulations showed that current sequestrationMercury (Hg) is considered a global environmental pollutant and its dominant form in the atmosphere – gaseous elemental Hg – has a loOngcaetmaonspShecriicernescideence time (6 to24 months), allowing for global redistribution (Schroeder and Munthe, 1998; Fitzgerald et al, 1998; Coughenour and of Hg in the contiguous US accounted for 15 230 metric tons of Hg in the top 0–40 cm of soils, or for over 300 000 met-Chen, 1997)
Our modelling simulations are based on the Community Land Model, version 3.5 (CLM3.5) (Oleson, 2004; Oleson et al, 2008), which is predominantly used in the Community Earth System Model (CESM) and Community Atmosphere Model (CAM)
It is important to note that our study was not intended to simulate process-driven and biogeochemical changes in Hg cycling under climate change, but rather was based on statistical relationships of Hg to soil C and other environmental variables observed in the field under present-day conditions
Summary
Latitude, and clay; and subsequently explored the sensitivity of soil C and soil Hg densities (i.e., areal-mass) to climate scenarios in which we altered annual precipitation, carbon dioxide (CO2) concentrations and temperature.Our model simulations showed that current sequestrationMercury (Hg) is considered a global environmental pollutant and its dominant form in the atmosphere – gaseous elemental Hg – has a loOngcaetmaonspShecriicernescideence time (6 to24 months), allowing for global redistribution (Schroeder and Munthe, 1998; Fitzgerald et al, 1998; Coughenour and of Hg in the contiguous US accounted for 15 230 metric tons of Hg in the top 0–40 cm of soils, or for over 300 000 met-Chen, 1997). Many natural sources emit Hg into the atmosphere – including volcanic sources, biomass burning and ric tons when extrapolated globally. US soil Hg pools were most sensitive to changes in precipitation because of strong effects on soil C pools, plus a direct surface evasion – but during the last 150 years, atmospheric. Soil Hg pools were predicted to increase beyond present-day values following, coal burning, waste incineration and industrial processes
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