Mercury budget of a small forested boreal catchment in southeast Norway

Abstract

We present input and output fluxes of total mercury (Hg tot) and methyl mercury (MeHg) based on throughfall, litterfall and stream water samples from 2004/2005 from a small forested catchment (Langtjern) in Norway. Hg tot input via throughfall and litterfall was estimated to 6.7 and 2.7 µg m − 2 yr − 1 , respectively, which is considerably lower than previously reported from other boreal catchments in Scandinavia. A likely cause for the low input flux is the sparseness and low productivity of the forest in the Langtjern catchment, with less atmospheric scavenging and lower litterfall fluxes than previously studied sites. In addition there has been a general decrease in mercury (Hg) in the atmosphere on the northern hemisphere in the last decade. The estimated output flux of Hg tot with surface water was 2.5 µg m − 2 yr − 1 , which is comparable to what has been reported elsewhere. The ratio of Hg tot output flux to input flux was 26%, which is considerably higher than reported from other sites. This illustrates that catchment properties have greater importance for surface water export of Hg than the current atmospheric input. The estimated total soil pool of Hg tot in the catchment was 17.4 mg m − 2 . This corresponds to roughly 8000 years of the current surface water output flux and 2000 years of the current input flux.