Abstract

In 2014, on 31 August and 1 September, the emissions of CH₄, CO₂, and O₂ gases were measured six times using the closed chamber method from exposed tidal flat sediments in the same position relative to the low point of the tidal cycle in the Eoeun-ri, Taean-gun, on the Mid-western Coast of Korea. The concentrations of CH₄ in the air sample collected in the chamber were measured using gas chromatography with an EG analyzer, model GS-23, within 6 hours of collection, and the other gases were measured in real time using a multi-gas monitor. The gas emission fluxes (source (+), and sink (-)) were calculated from a simple linear regression analysis of the changes in the concentrations over time. In order to see the surrounding parameters (water content, temperature, total organic carbon, average mean size of sediments, and the temperature of the inner chamber) were measured at the study site. On the first day, across three measurements during 5 hours 20 minutes, the observed CO₂ flux absorption was -137.00 to -81.73 mg/m²/hr, and the O₂ absorption, measured simultaneously, was -0.03 to 0.00 mg/m²/hr. On the second day using an identical number of measurements, the CO₂ absorption was -20.43 to -2.11 mg/m²/hr, and the O₂ absorption –0.18 to -0.14 mg/m²/hr. The CH₄ absorption before low tide was –0.02 mg/m²/hr (first day, Pearson correlation coefficient using the SPSS statistical analysis is –0.555(n=5, p=0.332, pronounced negative linear relationship)), and –0.15 mg/m²/hr (second day, -0.915(n=5, p=0.030, strong negative linear relationship)) on both measurement days. The emitted flux after low tide on both measurement days reached a minimum of +0.00 mg/m²/hr (+0.713(n=5, p=0.176, linear relationship which can be almost ignored)), and a maximum of +0.03 mg/m²/hr (+0.194(n=5, p=0.754, weak positive linear relationship)) after low tide. However, the absolute values of the CH₄ fluxes were analyzed at different times. These results suggest that rate for CH₄ fluxes, even the same time and area, were influenced by changes in the tidal cycle characteristics of surface sediments for understanding their correlation with these gas emissions, and surrounding parameters such as physiochemical sediments conditions.

Keywords closed chamber, continuous observation, CH₄ flux, sediment parameters, tidal flat