Nitrate was the dominant form of dissolved nitrogen in stream waters in Nagano Prefecture. Nitrate concentration showed a large geographical variation, ranging from 0.02 to 1.20 mg N L-1. Although there are significant negative relationships between nitrate concentration and altitude or annual precipitation, artificial influence accompanying with rainfall has not yet been confirmed on nitrate concentration in stream waters in Nagano Prefecture. In the Chikuma and Tenryu Rivers, dissolved organic nitrogen was observed in addition to the dominant nitrate. Dissolved total nitrogen concentration was around 1.5 mg N L-1 in the middle part of the both rivers. Nitrogen stable isotope ratio of periphyton increased downstream in the Chikuma River, whereas it was high in the upper reach and then decreased downstream in the Tenryu River. Nitrogen sources might shift from agricultural and mountain origins to sewage and livestock waste in the Chikuma River. Nitrogen derived from a sewage treatment system mainly contributed to the river nitrogen in the upper reach of the Tenryu River.
