[Deposition of Sulfur, Nitrogen and Mercury in Two Typical Forest Ecosystems in Southern China]

Bulk precipitation collectors and canopy throughfall collectors were applied to measure the deposition of sulfur, nitrogen, and mercury at two forest ecology stations, Qianyanzhou (QYZ) in Jiangxi Province and Huitong (HT) in Hunan Province, from December 2013 to November 2014. During the observation period, the volume weighted average concentrations of SO₄^2--S, NO₃^--N, NH₄⁺-N, and Hg at QYZ station were 1.89 mg·L^-1, 0.957 mg·L^-1, 0.401 mg·L^-1, and 12.5 ng·L^-1 in the bulk precipitation, respectively, and 2.39 mg·L^-1, 1.18 mg·L^-1, 0.897 mg·L^-1, and 22.2 ng·L^-1 in the throughfall, respectively. The concentrations of these components increased by different proportions for the bulk precipitation compared to the throughfall. At HT station, the average concentrations of SO₄^2--S, NO₃^--N, NH₄⁺-N, and Hg in the throughfall were 2.93 mg·L^-1, 1.60 mg·L^-1, 0.502 mg·L^-1, and 22.0 ng·L^-1, respectively. In addition, atmospheric deposition fluxes based on the throughfall were 3.56 g·(m²·a)^-1 for sulfur, 3.02 g·(m²·a)^-1 for nitrogen, and 30.6 μg·(m²·a)^-1 for mercury at QYZ station, while the corresponding fluxes were 6.18 g·(m²·a)^-1, 4.48 g·(m²·a)^-1, and 37.3 μg·(m²·a)^-1 at HT station. The deposition rates of all three elements were the highest in summer. The contribution of dry deposition to the total deposition of mercury was similar to that of wet deposition, while wet deposition contributed more to the total deposition of sulfur and nitrogen than did dry deposition. Unlike sulfur and nitrogen depositions, which were mainly derived from anthropogenic sources, mercury deposition might have a greater contribution from natural sources, especially at HT station.