Nitrous oxide in brackish Lakes Shinji and Nakaumi, Japan

• DOI: 10.1007/s102010170008
• Publication Date: 2002-10-15T14:53:15Z
• Authors: Yukiko Senga; Yasushi Seike; Kazuo Mochida; Kaoru Fujinaga; Minoru Okumura
• Keywords: Halocline; Epilimnion; Nitrous oxide

Nitrous oxide (N2O) was measured monthly from September 1997 to August 1998 in the brackish Lakes Shinji and Nakaumi, Japan. N2O (5–37 μg N l−1) was supersaturated in the overlying water on lake sediments from October 1997 to January 1998. The N2O concentration in the hypolimnion was higher than that in the epilimnion on 17 October 1997, when N2O was first observed in a water column of Lake Nakaumi. Afterward, N2O was almost uniform throughout the water column and then disappeared on 16 February 1998. On the one hand, large amounts of N2O were found throughout the year in the interstitial water in Lake Shinji, where a high concentration of nitrate was discharged from the Hii River. On the other hand, in Lake Nakaumi, stratified by halocline, a high concentration of N2O was observed in the interstitial water only from winter to spring. N2O concentrations in the interstitial water were about 10 to 1000 times as large as those in the overlying water. These results imply that N2O was mainly produced at the sediment-water interface and was diffused to the overlying water. It was also suggested that the accumulation of N2O in the sediment-water system was accelerated by a high concentration of hydrogen sulfide.