Nitrogen metabolism in the brackish Lake Nakanoumi. IV. Seasonal variation of nitrate nitrogen.

• DOI: 10.3739/rikusui.51.137
• Publication Date: 2011-06-09T03:51:32Z
• Authors: Yasushi SEIKE; Kunio KONDO; Hiroshi HASHITANI; Minoru OKUMURA; Kaoru FUJINAGA; Yoshio DATE
• Keywords: 0106 biological sciences; 13. Climate action; 01 natural sciences; 6. Clean water; 0104 chemical sciences

The seasonal variation of nitrate in the upper layer in the brackish Lake Nakanoumi has been investigated by the analysis of the data collected monthly during the period of 1976-1986. Upward trends in nitrate concentration were found in the colder season (January to March), and also in the rainy season (July). In contrast to nitrate, chlorinity decreased at the same time.A significant negative correlation between nitrate concentration and chlorinity in the surface water in Lake Nakanoumi was found in January, February, March and July. In addition, from the analysis of the correlation between the increment of nitrate concentration in the surface water and cumulative rainfall, it was concluded that the accumulation of nitrate in the upper layer is mainly caused by discharge from the rivers into the lake through rainfall and melted snow.