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Title: Investigation of natural methyl bromide (CH3Br) fluxes from temperate salt marsh and woodland ecosystems
Author: Drewer, Julia
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2007
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In this project, field measurements and controlled experiments were used to investigate the magnitude of, and controls on, some terrestrial sources of CH3Br to help in assessing global fluxes. The influence of factors such as temperature, soil properties, sunshine level, plant species and water table, and correlation to methane (CH­4) fluxes, were investigated. Field measurements were carried out using eight static flux chapters installed in pairs in the lower and upper areas of a salt marsh in East Lothian (Scotland) and four at a woodland site in Edinburgh. Mean annual measured net CH3Br emissions from the salt marsh were 350 ng m-2 h-1, with a large variability in fluxes from zero to ~4000 ng m-2 h-1, which increased seasonally. Summer emissions were on average about three times higher than winter emissions. Variation in CH3Br fluxes was larger between individual chambers indifferent pairs at the same salt marsh area (upper or lower) than between the two areas. There was also a strong association between sunny conditions and the timings of the frequent peaks in CH3Br emissions from the high emitting chambers above the general annual trend. There was a distinct diurnal variation in CH3Br fluxes from the salt marsh chambers throughout the year, also strongly correlated to the solar flux, showing highest emissions at mid-day and lowest at night. Salt marsh CH3Br fluxes were highly spatially variable, with a small proportion of “hot spots” accounting for the bulk of the spatially-integrated net emissions. There was no obvious explanation for the spatial heterogeneity of CH3Br emissions. Net CH3Br fluxes at the woodland site were an order of magnitude lower than at the salt marsh site, fluctuating between net uptake and net emission and with a mean in annual measured emissions (minimum and maximum in parentheses) of 27 (-73-279) ng m2 h-1. Net fluxes from the woodland site showed no seasonal trend and only fairly small diurnal variation. There were no or only modest correlations of net CH3Br fluxes with air and soil temperature, CH4 flux and water table depth. Scaling-up the salt marsh CH3Br fluxes from this work globally gave estimated annual emissions of 1 (0.5-3) Gg y-1, which was only ~10% of the global salt marsh emission estimate regularly quoted in the methyl bromide literature. In contrast, the emissions from the temperate woodland gave a global average of 2.7 (1.3-5) Gy y-1 which contradicted the common assumption that woodland soils are only sinks for CH3Br. Global annual net CH3Br fluxes from leaf litter were calculated to be 0.9 (-1.3-4) Gg y-1 which was within the range quoted in the literature, and from conifer needles to 5.3 (1.5-11.6) Gy y-1, slightly higher than previously reported.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available