Seasonal mass balance of halogens in simulated rice paddies

Abstract

[1] Halogens released from soil reservoirs to the atmosphere play important roles in atmospheric chemistry, including ozone loss and aerosol formation. Closed system experiments to determine controlling factors in halogen movement between the pedosphere, hydrosphere, terrestrial biosphere, and atmosphere are needed. This paper presents results from a closed system experiment on simulated rice paddies. It was observed that most water-extractable (bioavailable), halogens were swept downward from the surface during the initial watering pulse ($50, 70, and 75% of chloride, bromide, and iodide in unadulterated soils). Soil halogens were sequestered by rice plants with 28, 4, and 24% of the remaining bioavailable chlorine, bromine, and iodine processed by the plant tissue by the end of the season. Of the bioavailable halogens taken into the rice plant, less than 1% of chlorine or bromine is volatilized as a methyl halide while over 90% of iodide is emitted as gaseous CH 3 I.

Environmental effects of ozone depletion and its interactions with climate change: Progress report, 2005

“…51 New information that becomes available about these will improve existing models and our understanding of its involvement in atmospheric processes. 52,53…”

Characterization of methyl bromide and methyl chloride fluxes at temperate freshwater wetlands

“…Peak emissions were generally observed in early summer (June–July). In addition to temperature and PAR, seasonal trends in CH 3 X emission may also be linked to (a) plant biomass, which is at a minimum (or absent) during the winter months, rapidly increases at the start of the growing season and peaks at the end of the growing season, or (b) stages of the plant growth cycle, as observed for CH 3 X emissions from rice paddies [ Redeker et al ., ]. The observation of seasonal trends in CH 3 X emissions at Scottish wetlands is consistent with other long‐term measurements at temperate peatlands [ White et al ., ] and saltmarshes [ Drewer et al ., ; Blei et al ., ].…”