title: Regional comparison of nitrogen export to Japanese forest streams.
abstract: Nitrogen (N) emissions in Asian countries are predicted to increase over the next several decades. An understanding of the mechanisms that control temporal and spatial fluctuation of N export to forest streams is important not only to quantify critical loads of N, N saturation status, and soil acidification N dynamics and budgets in Japanese forested watersheds is not clear due to the lack of regional comparative studies on stream N chemistry. To address the lack of comparative studies, we measured inorganic N (nitrate and ammonium) concentrations from June 2000 to May 2001 in streams in 18 experimental forests located throughout the Japanese archipelago and belonging to the Japanese Union of University Forests. N concentrations in stream water during base flow and high flow periods were monitored, and N mineralization potential in soil was measured using batch incubation experiments. Higher nitrate concentrations in stream water were present in central Japan, an area that receives high rates of atmospheric N deposition. In northern Japan, snowmelt resulted in increased nitrate concentrations in stream water. The potential net N mineralization rate was higher in surface soil than in subsurface soil, and the high potential for N mineralization in the surface soil partly contributed to the increase in nitrate concentration in stream water during a storm event. Regional differences in the atmospheric N deposition and seasonality of precipitation and high discharge are principal controls on the concentrations and variations of nitrates in stream water in forested watersheds of Japan.
authors.affiliation: Northern Forestry Research and Development Office, Field Science Center for Northern Biosphere, Hokkaido, Nayoro, Japan. shiba@exfor.agr.hokudai.ac.jp
authors.forename: H
authors.initials: H
authors.lastname: Shibata
authors.forename: K
authors.initials: K
authors.lastname: Kuraji
authors.forename: H
authors.initials: H
authors.lastname: Toda
authors.forename: K
authors.initials: K
authors.lastname: Sasa
mesh_terms: D000641:Ammonia / Q000032:analysis; D017753:Ecosystem; D005618:Fresh Water / Q000737:chemistry; D005843:Geography; D007564:Japan; D009566:Nitrates / Q000032:analysis; D009584:Nitrogen / Q000032:analysis; D012621:Seasons; D012987:Soil / Q000032:analysis; D014197:Trees / Q000737:chemistry; D014887:Weather
chemical_list: D009566:Nitrates; D012987:Soil; D000641:Ammonia; D009584:Nitrogen