Abstract
The effect of soil flooding on methylmercury (MeHg) production was studied by placing humus and peat with water in 40 liter vessels. Total mercury (Tot-Hg), MeHg, nutrients, total organic carbon (TOC) and color were measured in water. Potential mercury methylation and demethylation rates in water and in flooded soils (humus and peat) were measured using radiochemical methods under aerated and non-aerated conditions during a period of 117 days.
In general, the potential methylation in humus and peat were one order of magnitude higher than in the water phase. During the experiment, methylation increased in humus and in peat but decreased in water. Demethylation decreased in all compartments. Anoxis increased methylation in soils but not in the water phase. On the other hand, demethylation was clearly higher in anoxic conditions. Tot-Hg increased more rapidly than MeHg in the water of the vessels, and a more rapid MeHg increase was observed in peat vessels than in humus vessels. Highest concentrations of MeHg (5.42 ng/L peat, 7.98 ng/L humus) were measured in non-aerated vessels.
Water color correlated negatively with methylation in water but positively with MeHg concentrations, indicating that humic substances are the main MeHg carriers but are not active melhylating agents. Methylmercury fluxes to water (3.6–44 ng/m2*d) were of the same order of magnitude as those measured in field experiments in Canada and in a beaver lake in Finland but were notably higher than those fluxes from unflooded catchmets.
The results indicate that increased net methylation in flooded humus and peat soils, especially in anoxic conditions, is the main reason for increased MeHg concentrations in reservoirs.
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Porvari, P., Verta, M. Methylmercury production in flooded soils: A laboratory study. Water Air Soil Pollut 80, 765–773 (1995). https://doi.org/10.1007/BF01189728
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DOI: https://doi.org/10.1007/BF01189728