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

Several aspects of atmospheric emissions of mercury from contaminated wetla nds were studied in the floodplains along the river Elbe (Northern Germany) . The volatilization process manifests itself in a well behaved height prof ile of atmospheric mercury concentrations in the boundary layer around the soil/air interface (air and soil air). This profile was described by a deta iled 9-point vertical gradient, which follows the mathematical description c(Hg) = 27h(-0.5) above the ground. This power function relationship is dis cussed theoretically and validated by comparison to other atmospheric mercu ry 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 moist ure. A mechanism is proposed, which indicates the coupling between aquatic and atmospheric remobilization of mercury from soils, and thereby emphasize s that wetlands play an important role for mercury turnover in biogeochemic al cycles due to their characteristic properties. Finally, some estimates o f the long-term behavior of the emissions and their importance for the regi onal Hg budget are derived. (C) 2000 Elsevier Science Ltd. All rights reser ved.