Mercury dynamics and mass balance in a subtropical forest, southwestern China

Abstract

The mid-subtropical forest area in southwest China was affected by anthropogenic mercury (Hg) emissions over the past 3ĝ€decades. We quantified mercury dynamics on the forest field and measured fluxes and pools of Hg in litterfall, throughfall, stream water and forest soil in an evergreen broadleaved forest field in southwestern China. Total Hg (THg) input by the throughfall and litterfall was assessed at 32.2 and 42.9ĝ€μgĝ€mĝ'2ĝ€yrĝ'1, respectively, which was remarkably higher than those observed from other forest fields in the background of North America and Europe. Hg fluxes across the soil-air interface (18.6ĝ€mgĝ€mĝ'2ĝ€yrĝ'1) and runoff and/or stream flow (7.2ĝ€μgĝ€mĝ'2ĝ€yrĝ'1) were regarded as the dominant ways for THg export from the forest field. The forest field hosts an enormous amount of atmospheric Hg, and its reserves is estimated to be 25ĝ€341ĝ€μgĝ€m2. The ratio of output to input Hg fluxes (0.34) is higher compared with other study sites. The higher outputĝ€/ĝ€input ratio may represent an important ecological risk for the downstream aquatic ecosystems, even if the forest field could be an effective sink of Hg.