No abstract

Fluxes of major ions in rainfall (RF), throughfall plus stemflow (TF + SF), and stream water (SW) were measured for five water years in a small catchment of a Japanese cedar forest near the Sea of Japan. The fluxes of most ions in RF and in TF + SF, including the non-sea-salt constituents, increased from late autumn to midwinter owing to the seasonal westerly wind. The concentrations of most ions in SW showed no obvious seasonal trend during the study period, whereas NO À 3 concentrations were lowest in summer, with a small seasonality. The Ca 2+ and Mg 2+ outputs in SW were approximately 3.7 and 1.8 times the TF + SF inputs of these cations, respectively. The large net outputs of base cations in the catchment may indicate a decrease in the soil's acid-neutralizing capacity. Annual dissolved inorganic nitrogen inputs in RF and in TF + SF were 17.7 and 17.9 kg N ha −1 year −1 , respectively, which exceeded previously published thresholds in Europe and the U.S. (i.e., the values at which these inputs increased NO À 3 levels in SW) and equaled the highest level of nitrogen deposition previously reported in Japan. The NO À 3 concentrations in SW were relatively high even in summer. During high-precipitation events, NO À 3 concentrations in SW increased with increasing water discharge, and the pH decreased simultaneously during several events. Nitrogen deposition may contribute to the high NO À 3 concentrations in SW and the temporary acidification that occurred during the rain events.

Rapid industrialization in East Asia is causing adverse effects due to atmospheric deposition in terrestrial and freshwater ecosystems. Decreasing stream pH and alkalinity and increasing NO 3 -concentrations were observed throughout the 1990s in the forested Lake Ijira catchment in central Japan. We investigated these changes using data on atmospheric deposition, soil chemistry, stream water chemistry, and forest growth. Average atmospheric depositions (wet ? dry) of 0.83, 0.57, and 1.37 kmol ha -1 year -1 for hydrogen, sulfur, and nitrogen, respectively, were among the highest levels in Japan. Atmospheric deposition generally decreased before 1994 and increased thereafter. The catchment was acidsensitive; stream alkalinity was low (134 lmol c l -1 ) and pH in surface mineral soils decreased from 4.5 in 1990 to 3.9 in 2003. Stream NO 3 -concentration nearly doubled (from 22 to 42 lmol c l -1 ) from the late 1980s to the early 2000s. Stream NO 3 -concentration was

Since 1983, the Ministry of the Environment of Japan has conducted nation-wide acid deposition surveys. To investigate the effects of acid deposition on surface water, we used the nonparametric Mann-Kendall test to find temporal trends in pH, alkalinity, and electrical conductivity (EC) in more than 10 years of data collected from five lakes and their catchments (Lake Kuttara: northernmost; Lake Kamakita: near Tokyo; Lake Ijira: central; Lake Banryu: western; and Lake Unagiike: southernmost). The pH of Lake Ijira water has declined slightly since the mid-1990s, corresponding with the downward trends seen in the pH and alkalinity of the river water flowing into the lake. There were significant upward trends in the EC of both the lake and stream water; the same trends were also found for NO À 3 concentrations. These trends show evidence of acidification due to atmospheric deposition, and this is the first such finding in Japan based on significant long-term trends. Lake Ijira is located about 40 km north of the Chukyo industrial area near Nagoya. The annual depositions of H + , nss-SO 2À 4 , and NO À 3 in Lake Ijira were among the highest of all deposition monitoring sites, suggesting that this is the main cause of the Water Air Soil Pollut: Focus (2007) 7: [259][260][261][262][263][264][265][266]