Knowledge gaps of mercury (Hg) biogeochemical processes
in the
tropical rainforest limit our understanding of the global Hg mass
budget. In this study, we applied Hg stable isotope tracing techniques
to quantitatively understand the Hg fate and transport during the
waterflows in a tropical rainforest including open-field precipitation,
throughfall, and runoff. Hg concentrations in throughfall are 1.5–2
times of the levels in open-field rainfall. However, Hg deposition
contributed by throughfall and open-field rainfall is comparable due
to the water interception by vegetative biomasses. Runoff from the
forest shows nearly one order of magnitude lower Hg concentration
than those in throughfall. In contrast to the positive Δ199Hg and Δ200Hg signatures in open-field
rainfall, throughfall water exhibits nearly zero signals of Δ199Hg and Δ200Hg, while runoff shows negative
Δ199Hg and Δ200Hg signals. Using
a binary mixing model, Hg in throughfall and runoff is primarily derived
from atmospheric Hg0 inputs, with average contributions
of 65 ± 18 and 91 ± 6%, respectively. The combination of
flux and isotopic modeling suggests that two-thirds of atmospheric
Hg2+ input is intercepted by vegetative biomass, with the
remaining atmospheric Hg2+ input captured by the forest
floor. Overall, these findings shed light on simulation of Hg cycle
in tropical forests.