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Yakushima, facing at 800 km east of Shanghai in the East China Sea, is a tall cone-shaped island with seven exceeding 1800 m peaks. The prevailing winds of westrelie on the island blow mostly fromnorthwest and west. It has been exposed to acid rain of pH 4.7 and precipitation 8000 mm in the central highland. More than sixty mountainous streams were observed at downstream points seasonally for past twelve years. The alkalinity of streamwaters in the southwestern part was lower than others. The concentrations of SO42- in the northwestern part were higher than others. The high concentrations of SO42-, dissolved SiO2 and other ions in the southwestern part with high canopy density of evergreen broadleaved forest were caused by higher air temperature, less rainfall and higher evapotranspiration than other parts. The alkalinity, pH and EC in the catchment of north stream in the upstream branch of the R. Anboh became lower than those in the catchment of south stream. The height of catchment boundaries, the direction of the main axis of a catchment and the prevailing winds govern the influence of acid deposition on water quality of branch streams
Journal of Water and Environment Technology, Vol.3, No.2, 2005 - 169 - INFLUENCE DISTRIBUTIONS OF ACID DEPOSITION IN MOUNTAINOUS STREAMS ON A TALL CONE-SHAPED ISLAND, YAKUSHIMA S. Ebise* and O. Nagafuchi** *Dept. of Civil and Environmental Engineering System, Setsunan University, 17-8 Ikeda-Nakamachi, Neyagawa, Osaka, 572-8508, Japan **Dept. of Environmental System, Chiba Institute of Science, 3 Shiomi, Choshi, Chiba 288-0025 ABSTRACT Yakushima, facing at 800 km east of Shanghai in the East China Sea, is a tall cone-shaped island with seven exceeding 1800 m peaks. The prevailing winds of westrelie on the island blow mostly fromnorthwest and west. It has been exposed to acid rain of pH 4.7 and precipitation 8000 mm in the central highland. More than sixty mountainous streams were observed at downstream points seasonally for past twelve years. The alkalinity of streamwaters in the southwestern part was lower than others. The concentrations of SO 4 2- in the northwestern part were higher than others. The high concentrations of SO 4 2- , dissolved SiO 2 and other ions in the southwestern part with high canopy density of evergreen broadleaved forest were caused by higher air temperature, less rainfall and higher evapotranspiration than other parts. The alkalinity, pH and EC in the catchment of north stream in the upstream branch of the R. Anboh became lower than those in the catchment of south stream. The height of catchment boundaries, the direction of the main axis of a catchment and the prevailing winds govern the influence of acid deposition on water quality of branch streams. KEYWORDS Acid deposition; mountainous stream; influence distribution; cone-shaped; prevailing wind INTRODUCTION Yakushima, an island lying 800 km east of Shanghai on the boundary between the Pacific Ocean and East China Sea (Fig. 1), is a World Heritages Area and a National Park of Japan. Yakushima is famous for its yaku-sugi (Crytomeria japonica), one of which, called Jomon-sugi, is the oldest living organism in Japan. The prevailing winds on the island were northwestern (strongly so in winter) and western except during the short typhoon season, when the wind comes from the southeast. Consequently, Yakushima is exposed to acid deposition with an annual mean pH of 4.7 (MOE, 2004). The annual precipitation ranges 4300 mm at the coast to above 8000 mm in the central highland where seven peaks exceeds 1800 m. The tallest peak is Mt. Miyanouradake at 1935 m. The island has a steep mountainous landform and is covered with a thin soil layers overlying granite. Therefore, the soil’s ability to neutralize acid deposition is very weak (Ebise, 1996). Journal of Water and Environment Technology, Vol.3, No.2, 2005 - 170 - Figure 1 Yakushima Island and main rivers All 14,000 residents of the island live on the coast. There are no sources of artificial pollutants in the mountains, where the only visitors are mountain climber and backpackers. Back-trajectory and Pb-isotope trace methods show that most of the acid deposition coming from the Asia Continent is transported overseas by the prevailing westerlies in the upper air region, until it strikes the high mountains on the island. The major species in the acid deposition is sulfuric acid (Nagafuchi et al. 1995, 2001a, 2001b). The pH of wet deposition tends to be lower in winter (MOE, 2004). Here we present observations of geographic influence distribution of acid deposition, altitudinal distribution, distribution in the catchments of western streams and upstream catchment distributions in the five biggest streams for the past twelve years. Alkalinity, pH, electric conductivity (EC), total organic carbon, dissolved SiO 2 , inorganic cations and anions were measured as water quality indicators. INFLUENCE PATTERNS OF ACID DEPOSITION Yakushima (area of 503 km 2 ) is a tall, circular, cone-shaped island with many mountain folds, which give rise to mountain streams. More than sixty steep mountainous streams run almost straight in all directions from the center to the sea describing radii of a circle on a map (Ebise and Nagafuchi, 2002). We observed these streamwaters at downstream points on the same day every season for past twelve years. The water quality in these streams can be shown as in, Fig. 2(a)-(d) (fall in 2003), using the strait lines as vectors. The distribution of water quality indicators around the circle show distinctive features. The concentrations of SO 4 2- (Fig. 2(d)) were always higher in the northwestern streams. This shows that the load of SO 4 2- there is heavy, as the soil, rock and flora there are mostly similar to those in other parts of island. The values of pH were lower in the southwestern streams. The values of alkalinity and the concentrations of Ca 2+ and Mg 2+ were lower in the southern streams. These distributions result Journal of Water and Environment Technology, Vol.3, No.2, 2005 - 171 - mainly from the landform of the island, the distribution of acid deposition and the local meteorological conditions. Figure 2 Distributions of water quality downstream in all streams LOW pH AND HIGH EC IN THE WESTERN STREAMS In the catchments of the western streams the annual precipitation was lower and annual air temperature was higher than in the other parts. These streams had low pH, high EC, low alkalinity and high concentrations of ions and dissolved SiO 2 . Therefore, we made a detailed study of streamwater, soil water, and wet and dry depositions on the leaves of densely covered trees (Nagafuchi et al., 2002, 2003). Some wet and almost all dry depositions remains on the canopy of laurel forest in these catchments building up during dry weather until being washed off in the next rain. In particular, the mass of accumulated Cl - and SO 4 2- on the leaves was higher in November than in February (Fig. 3). Although the concentrations of inorganic ions in these streams were similar for the most part to those in other areas, the concentrations of Na + and Cl - were higher. Because the Cl - in the streamwater had an atmospheric origin and was concentrated on the canopy between rainfall events, SO 4 2- of atmospheric origin may be similarly concentrated. The concentration of dissolved SiO 2 due to the chemical weathering of Na-feldspar was also higher. Evaporation and the local influence distribution of acid deposition loads resulted in these distinctive features. Journal of Water and Environment Technology, Vol.3, No.2, 2005 - 172 - Figure 3 Accumulation mass of Cl - and SO 4 2- on the leaf in the western part. INFLUENCE DISTRIBUTIONS IN THE BIGGEST RIVER The biggest river, the Anboh (catchment of 86.1 km 2 ), runs down from near the peak of Mt. Miyanouradake to eastern shore. The Anboh in its upper stream has two branch streams, north and south. Mountains ranging from 1800 to 1935 m sit at the western boundary of the south branch. But, the mountains at the western and northern boundaries of the north branch are low, not exceeding 1400 m, and their slopes are gentle. Fig. 4 shows two vertical cross sections of the catchment of the north and south branch streams, and Table 1 shows the mean values of pH, EC and alkalinity in small branch streams between those catchments in 2003. The prevailing westerlies strike the high mountainous wall at the western boundary of the south branch stream, depositing their rain and pollutants mostly in the catchment to the west. But those, arriving in the catchment of the north branch stream, fall there. So, the acid deposition loads, particularly SO 4 2- , in the catchment of the south branch are lower than those in the north. The year 2003 was second driest year in the past twelve years, and our four seasonal observations showed little influence of direct runoff of ordinary storms. As all mountain streams were composed mostly of groundwater runoff, their capacity to neutralize acid deposition could be estimated as the values of alkalinity in the streamwaters. Long-term influence, which is judged by alkalinity during Journal of Water and Environment Technology, Vol.3, No.2, 2005 - 173 - groundwater runoff in streams, is important in term of the critical load of acid deposition to a catchment. Figure 4 Catchment of the upstream R. Anboh and vertical cross sections. The values of values of alkalinity, pH and EC in the small streams flowing into the north branch stream were lower (e.g. 40 % in alkalinity) than those in the south branch. The concentrations of almost all cations and anions in the small branches of the south branch were less than those in the north branch. The same distributions of alkalinity, pH and EC were also confirmed in the upstream catchment of the second biggest river, R. Miyanoura. Table 1 Comparison of alkaliniy (Alk. meq/l), pH and EC (mS/m) between north stream (n=20) and south stream (n=27) in upstream catchment of R. Anboh. North Stream (Left) South Stream (n=27) EC pH Alk. EC pH Alk. March 2.91 5.38 0.031 3.08 5.92 0.050 July 2.70 5.54 0.037 2.75 6.07 0.055 Sept. 2.75 5.61 0.042 2.95 6.12 0.060 Nov. 2.81 5.76 0.052 2.96 6.06 0.061 CONCLUSION We have observed the influence of acid deposition in mountain streams on a tall, cone-shaped island, Yakushima. As all the steep stream flow down radially from near the top of the high mountains, and the prevailing northwestern wind from the Asia Continent carries acid pollutants, the direction of stream course and height of catchment boundaries govern the distribution of acid deposition. These facts were made clear by the distribution patterns of water quality indicators in the mountain streams. Journal of Water and Environment Technology, Vol.3, No.2, 2005 - 174 - The high canopy density of evergreen broadleaved forest and the air temperature in the catchment of the western part of the island are responsible for the low pH and high concentrations of anions in the western streams. The height of catchment boundaries, the direction of the main axis of a catchment and the prevailing wind govern the influence of acid deposition on the water quality of branch streams. These features are caused mainly by the shape and isolation of the island. REFERANCE Ebise S. (1996) Estimation on effects of acid rain by observation of mountainous river waters during dry-weather day and storm event in Yakushima Island, J. Environ. Sci., 9, 377-391. Ebise S. and Nagafuchi O. (2002) Runoff characteristics of water quality and influence of acid rain on mountainous streamwaters on Yakushima island, Jap. J. Limnol., 63, 1-10. Ministry of Environment (MOE) (2004) Report on comprehensive observation of acid deposition, p.432. Nagafuchi, O. et al. (1995) Analysis of long-range transported acid aerosol in rime found at Kyushu mountainous region, Japan, Wat., Air & Soil Pollution, 85, 2351-2356. Nagafuchi, O., Mukai, H., Ebise, S., Inoue T. and Koga, M. (2001) Runoff of acidic substances originated from atmospheric deposition on the Yakushima Island, a World Natural Heritage Site, Wat. Sci. and Tech., 44, 57-62. Nagafuchi, O., Mukai, H. and Koga, M. (2001a) Black acidic rime ice in the remote island of Yakushima, a World Natural Heritage Area, Wat., Air & Soil Pollution, 130, 1565-1570. Nagafuchi O., H. Kakimoto, S. Ebise and M. Ukita (2002b) Effects of forests on mountainstream water quality, Jap. J. Limnol., 63, 11-19. Nagafuchi O., et al. (2003) Effects of acid deposition on the water quality formation of mountainous streams in the western part of Yakushima Island, a World National Heritage Site, J. Jap. Soc. on Wat. Environ., 26, 159-166. . South Stream (n=27) EC pH Alk. EC pH Alk. March 2.91 5 .38 0. 031 3. 08 5.92 0.050 July 2.70 5.54 0. 037 2.75 6.07 0.055 Sept. 2.75 5.61 0.042 2.95 6.12 0.060. ranges 430 0 mm at the coast to above 8000 mm in the central highland where seven peaks exceeds 1800 m. The tallest peak is Mt. Miyanouradake at 1 935 m. The