Regional distribution of natural stream nitrate in central Japan

Over 60 natural streams with forested catchments were surveyed for nitrate (NO(3)(-)) concentration in central Japan. Stream NO(3)(-) concentrations showed a clear zonal gradient with a range nearly as large as 100-fold, where their small seasonal variations (av. CV = 27%) justified respective statuses. Elevated NO(3)(-) concentrations (more than 70 muM) described a distribution of N saturation along a course of polluted air advection in the Kanto Plain. The extent of NO(3)(-) leaching from forests was not proportional to atmospheric N deposition probably because of ecosystem N retention. A dependency of NO(3)(-) level on the watershed altitude and quite constant delta (15)N of stream NO(3)(-) over a wide NO(3)(-) range were observed, which could be also related to this cause.