Understanding mercury (Hg) complexation with soil organic
matter
is important in assessing atmospheric Hg accumulation and sequestration
processes in forest ecosystems. Separating soil organic matter into
particulate organic matter (POM) and mineral-associated organic matter
(MAOM) can help in the understanding of Hg dynamics and cycling due
to their very different chemical constituents and associated formation
and functioning mechanisms. The concentration of Hg, carbon, and nitrogen
contents and isotopic signatures of POM and MAOM in a deglaciated
forest chronosequence were determined to construct the processes of
Hg accumulation and sequestration. The results show that Hg in POM
and MAOM are mainly derived from atmospheric Hg0 deposition.
Hg concentration in MAOM is up to 76% higher than that in POM of broadleaf
forests and up to 60% higher than that in POM of coniferous forests.
Hg accumulation and sequestration in organic soil vary with the vegetation
succession. Variations of δ202Hg and Δ199Hg are controlled by source mixing in the broadleaf forest
and by Hg sequestration processes in the coniferous forest. Accumulation
of atmospheric Hg and subsequent microbial reduction enrich heavier
Hg isotopes in MAOM compared to POM due to the specific chemical constituents
and nutritional role of MAOM.