Contribution of Ebullition to Methane and Carbon Dioxide Emission from Water between Plant Rows in a Tropical Rice Paddy Field

Although bubble ebullition through water in rice paddy fields dominates direct methane (CH4) emissions from paddy soil to the atmosphere in tropical regions, the temporal changes and regulating factors of this ebullition are poorly understood. Bubbles in a submerged paddy soil also contain high concentrations of carbon dioxide (CO2), implying that CO2 ebullition may occur in addition to CH4 ebullition. We investigated the dynamics of CH4 and CO2 ebullition in tropical rice paddy fields using an automated closed chamber installed between rice plants. Abrupt increases in CH4 concentrations occurred by bubble ebullition. The CO2 concentration in the chamber air suddenly increased at the same time, which indicated that CO2 ebullition was also occurring. The CH4 and CO2 emissions by bubble ebullition were correlated with falling atmospheric pressure and increasing soil surface temperature. The relative contribution of CH4 and CO2 ebullitions to the daily total emissions was 95–97% and 13–35%, respectively.

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Comparison of Closed Chamber and Eddy Covariance Methods to Improve the Understanding of Methane Fluxes from Rice Paddy Fields in Japan

Atmosphere ◽

10.3390/atmos9090356 ◽

2018 ◽

Vol 9 (9) ◽

pp. 356 ◽

Cited By ~ 6

Author(s):

Nongpat Chaichana ◽

Sonoko Bellingrath-Kimura ◽

Shujiro Komiya ◽

Yoshiharu Fujii ◽

Kosuke Noborio ◽

...

Keyword(s):

Eddy Covariance ◽

Rice Paddy ◽

Paddy Fields ◽

Closed Chamber ◽

Cropping Season ◽

Greenhouse Gas Flux ◽

Land Use Types ◽

Methane Fluxes ◽

Footprint Analysis ◽

Rice Paddy Fields

Greenhouse gas flux monitoring in ecosystems is mostly conducted by closed chamber and eddy covariance techniques. To determine the relevance of the two methods in rice paddy fields at different growing stages, closed chamber (CC) and eddy covariance (EC) methods were used to measure the methane (CH4) fluxes in a flooded rice paddy field. Intensive monitoring using the CC method was conducted at 30, 60 and 90 days after transplanting (DAT) and after harvest (AHV). An EC tower was installed at the centre of the experimental site to provide continuous measurements during the rice cropping season. The CC method resulted in CH4 flux averages that were 58%, 81%, 94% and 57% higher than those measured by the EC method at 30, 60 and 90 DAT and after harvest (AHV), respectively. A footprint analysis showed that the area covered by the EC method in this study included non-homogeneous land use types. The different strengths and weaknesses of the CC and EC methods can complement each other, and the use of both methods together leads to a better understanding of CH4 emissions from paddy fields.

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Depth distribution of radiocesium in Fukushima paddy fields and implications for ongoing decontamination works

SOIL Discussions ◽

10.5194/soild-1-401-2014 ◽

2014 ◽

Vol 1 (1) ◽

pp. 401-428

Author(s):

H. Lepage ◽

O. Evrard ◽

Y. Onda ◽

I. Lefèvre ◽

J. P. Laceby ◽

...

Keyword(s):

Power Plant ◽

Nuclear Power ◽

Soil Surface ◽

Rice Paddy ◽

Organic Content ◽

Paddy Fields ◽

Organic Carbon Content ◽

River Channels ◽

Depth Migration ◽

Rice Paddy Fields

Abstract. Large quantities of radiocesium were deposited across a 3000 km2 area northwest of the Fukushima Dai-ichi nuclear power plant after the March 2011 accident. Although many studies have investigated the fate of radiocesium in soil in the months following the accident, the potential migration of this radioactive contaminant in rice paddy fields requires further examination after the typhoons that occurred in this region. Such investigations will help minimize potential human exposure in rice paddy fields or transfer of radioactive contaminants from soils to rice. Radionuclide activity concentrations and organic content were analysed in 10 soil cores sampled from paddy fields in November 2013, 20 km north of the Fukushima power plant. Our results demonstrate limited depth migration of radiocesium with the majority concentrated in the uppermost layers of soils (< 5 cm). More than 30 months after the accident, 81.5 to 99.7% of the total 137Cs inventories was still found within the < 5 cm of the soil surface, despite cumulative rainfall totalling 3300 mm. Furthermore, there were no significant correlations between radiocesium migration depth and total organic carbon content. We attributed the maximum depth penetration of 137Cs to maintenance (grass cutting – 97% of 137Cs in the upper 5 cm) and farming operations (tilling – 83% of 137Cs in the upper 5 cm). As this area is exposed to erosive events, ongoing decontamination works may increase soil erodibility. We therefore recommend the rapid removal of the uppermost – contaminated – layer of the soil after removing the vegetation to avoid erosion of contaminated material during the subsequent rainfall events. Remediation efforts should be concentrated on soils characterised by radiocesium activities > 10 000 Bq kg−1 to prevent the contamination of rice. Further analysis is required to clarify the redistribution of radiocesium eroded on river channels.

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