NISHIO Fumihiko Chiba University, The Environment Remote Sensing Center, Professor, 環境リモートセンシング研究センター, 教授 (40044789)
KUSHIDA Keizi Hokkaido University, Institute of Low Temperature Science, Assistant, 低温科学研究所, 助手 (90291236)
FUKUDA Masami Hokkaido University, Institute of Low Temperature Science, Professor, 低温科学研究所, 教授 (70002160)
|Budget Amount *help
¥4,500,000 (Direct Cost : ¥4,500,000)
Fiscal Year 1999 : ¥600,000 (Direct Cost : ¥600,000)
Fiscal Year 1998 : ¥600,000 (Direct Cost : ¥600,000)
Fiscal Year 1997 : ¥3,300,000 (Direct Cost : ¥3,300,000)
Few cases of research have been conducted on methane gas contained in lake ice. Such research was carried out for lakes and swamps in Siberia, but it was limited to local, segmented observation, and no principle theory was produced. This study was characterized by sequential observation of air bubbles which accumulate in the form of annual rings in clear lake ice as ice thickness increases, conducted under favorable meteorological conditions for investigation, which made measurement of methane gas quantity contained in air bubbles possible.
This study intends to improve the accuracy of assessments of methane flux from a wetland area through the measurement of methane quantities surfacing from the bottom of lakes and ponds existing across a wetland.
The observation was conducted in Lake Akanuma (43°06' 20" N. long., 144° 21' 50" E. lat.), located in the center of Kushiro Marsh. Methane gas quantities were calculated based on the concentration and volume of methane gas surfacing from the l
ake bottom and contained in bubbles within the ice over the lake. Bubbles were collected using a method established by Fig.5. In this method, bubbles are collected by dissolving a cut-ice block containing bubbles in a saturated sodium chloride solution.
Gas samples were analyzed on a Shimadzu GC-14BTCD Gas Chromatograph for gas concentrations. Water chemistry data (temperature, pH, specific conductivity, dissolved oxygen and oxidation reduction potential) were collected with a TOA : WQC-22A Multi-Parameter Water Quality Probe in situ.
The quantity of bubbles incorporated into the ice over Lake Akanuma over 15 days from December 12 through 27, 1997, was 1,555 lit. If the methane concentration within the bubbles is 60%, the bubbles may contain 0.75 kg (or 0.54 mg/m2 day) of methane.
However, the volume of bubbles had to be estimated from their appearances, although this was conducted based on long-time bubble collecting experiences. Also, it is possible that some bubbles were first contained in ice, went through the triple-grain boundary within the crystalline structure of ice, and dispersed into the atmosphere. The above-mentioned values thus may deviate by a fraction or even several multiples. It is necessary to improve examination methods to realize higher accuracy in assessment. Less