Environmental factors influencing the load of long-range transported air pollutants on Pinus amamiana in Yakushima Island, Japan

With the industrialization in East Asia, greater amounts of ozone and acidic aerosols are transported to Japan. Yakushima Island (30°20′N, 130°31′E) is affected directly by long-range transboundary air pollution from the continent because there are no industrial areas and sources of pollution between the continent and the island. Recently, there has been a significant decline of Pinus amamiana in the island and the actual condition of air pollution was investigated. A significant amount of air pollutants were detected in winter. The daily mean tropospheric O₃ concentration was nearly 100 ppb in winter. A large amount of non-sea salt sulfate (nss-SO₄^2-) was deposited on the needle surfaces in the northwest part of the island and dry deposition rates of SO₄^2- were remarkably higher in February than in November. About half of the increase in SO₄^2- was nss-SO₄^2- and the rate in February was over four to five times as high as that in November. The load of dry deposition on the crown of trees was strongly influenced by the topographic position of the slope. The amount of deposited SO₄^2- was larger on trees growing on ridges and the tendency of P. amamiana to grow on ridges where it sticks out over 20 m enhances the load of dry deposition and O₃ on the needle surfaces. The potassium leakage and ethylene emission from needles were remarkably increased and the needle mass per area decreased from November to February. It was suggested that the additional input of nss-SO₄^2- acidifies the needle surface and accelerates leaf surface deterioration and leaching from needles and soils.