Plant mercury accumulation and litter input to a Northern Sedge-dominated Peatland

Abstract

Abstract. Plant foliage plays an essential role in accumulating mercury (Hg) from the atmosphere and transferring it to soils in terrestrial ecosystems, and many studies have focused on forested ecosystems. Hg input from plants to northern peatland peat soils has not been nearly as well studied and is likely equally important from a mass balance perspective. In this study, we investigated the accumulation of atmospheric Hg by the dominant plant species, few-seeded sedge (Carex oligosperma Michx.), wire sedge (Carex lasiocarpa Ehrh), tussock sedge (Carex stricta Lamb.), and sweet gale (Myrica gale L.), in a boreal sedge-dominated peatland. Foliar Hg concentrations decreased early in the growing season due to growth dilution, and after that they were subsequently positively correlated with leaf age (time). Hg concentrations were 1.4–1.7 times higher in sweet gale than in sedges. A leaching experiment showed that sweet gale leached less Hg but more bioaccessible dissolved organic matter (DOM) by mass than sedges. Leaching of Hg was positively related to the aromaticity of DOM in leachate, suggesting the importance of DOM with higher aromaticity in controlling Hg mobility. Annual inputs of Hg through senesced leaf material to peat soils were 9.88, 1.62, and 8.29 mg ha−1 yr−1 for sweet gale, tussock sedge, and few-seeded sedge and wire sedge, respectively. Future investigations into foliar Hg accumulation and input from other plant species to the sedge-dominated peatland are needed to estimate the annual Hg inputs precisely.