Abstract
Vegetation uptake of gaseous elemental mercury (Hg(0)) is the main deposition pathway to terrestrial environments. However, the fluxes and processes of forest-atmosphere Hg(0) exchange remain ill-constrained, especially in rainforests. To help address this, we used the 1 ha Masoala Rainforest hall of the Zoo Zurich as a dynamic flux chamber to measure net rainforest Hg(0) fluxes and even calibrate Hg(0) deposition velocities with turbulence measurements. The net Hg(0) flux correlated well with CO(2) assimilation, showing peak Hg(0) uptake at noon. The interquartile range of Hg(0) uptake spanned from 1.69 to 3.45 ng m(-2) h(-1) during the day and from 0.01 to 0.44 ng m(-2) h(-1) at night. The study results revealed a Hg(0)-specific canopy resistance (R(c) = 1000 s m(-1)), which underlined the importance of stomatal uptake as a dominant Hg(0) deposition pathway in the rainforest. Even though a dynamic flux chamber, however large, is only an approximation of a real rainforest, our findings underline the value of whole-rainforest flux studies both for constraining Hg exchange with the atmosphere and resolving the role of specific mechanisms.