Mechanism and significance of mercury volatilization from contaminated floodplains of the German river Elbe

Several aspects of atmospheric emissions of mercury from contaminated wetlands were studied in the floodplains along the river Elbe (Northern Germany). The volatilization process manifests itself in a well behaved height profile of atmospheric mercury concentrations in the boundary layer around the soil/air interface (air and soil air). This profile was described by a detailed 9-point vertical gradient, which follows the mathematical description c(Hg)=27h−0.5 above the ground. This power function relationship is discussed theoretically and validated by comparison to other atmospheric mercury height profiles described in the literature. Understanding of the phase transfer mechanism is improved by the finding that rain events increase the mercury flux to the atmosphere up to threefold due to increased soil moisture. A mechanism is proposed, which indicates the coupling between aquatic and atmospheric remobilization of mercury from soils, and thereby emphasizes that wetlands play an important role for mercury turnover in biogeochemical cycles due to their characteristic properties. Finally, some estimates of the long-term behavior of the emissions and their importance for the regional Hg budget are derived.