Studies on the features of dissolved constituents in Ukawa River system Part 2 ： Seasonal variations of nitrate concentration

摘要

In recent years, there has been grate concerns for the nitrogen saturation phenomenon in forest ecosystems caused　by increased wet and dry deposition of nitrogen compounds　emitted　from the combustion of fossil fuels. The nitrogen saturation phenomenon is considered to be that increased nitrogen flow out to forest stream not only in the non-growth period but also in the growth period of forest plants. In this study, in order to understand the current situation of nitrogen saturation phenomenon from nitrate concentrations and their seasonal variations in upper and middle streams of Ukawa river, which is flowing through Kashiwazaki City, Niigata Prefecture, the river water was sampled from the eleven sites for once a month from June 2009 to February 2011, and was determined the major soluble constituents including nitrate and alkalinity. As a result, it was revealed that nitrate concentration has a clear seasonal variation with higher in winter and lower in summer, however, nitrate were detected as 0.5-1.5 mg/L levels in summer when biological actives are lively, so the nitrogen saturation phenomenon in the forest water shed of Ukawa river is considered to be undeniable situation.