Seasonality, Sinks and Sources of Methyl Chloride and Methyl Bromide From the Tallgrass Prairie
Abstract
Net and gross fluxes of methyl chloride (CH3Cl) and methyl bromide (CH3Br) were measured between 2006 and 2008 from a variety of vegetation types and climatic conditions at a tallgrass prairie (Konza Prairie, Manhattan, KS). Gross consumption and production rates were calculated using a stable isotope tracer technique that entailed a small addition of 13C labeled methyl halides, and an inert tracer, at the beginning of each chamber experiment. Overall, the tallgrass prairie was found to be a net sink for both atmospheric CH3Cl and CH3Br (gross rates were -581.1 /pm 249.7 nmol m-2d-1 and -13.8 /pm 5.5 nmol m-2d-1). The average uptake ratio of CH3Cl to CH3Br was 42.7 /pm 9.2, which was lower than the lower tropospheric concentration ratio of 59.3 /pm 5.5 at this site. Daytime and nighttime fluxes were not significantly different. Uptake rates were higher but more variable during the non-growing season outings, which were cooler and wetter than the growing season sampling times. Uptake fluxes ranged widely over small spatial scales and were correlated better with soil moisture than temperature. Burn frequency and total aboveground biomass of each site did not appear to influence uptake of CH3Cl or CH3Br. Tallgrass prairie consumed CH3Cl and CH3Br at a lower rate than the average published values for grassland soils. Live Amorpha canescens and A. fruticosa produced both CH3Cl and CH3Br but at significantly different CH3Cl:CH3Br ratios (27.5 /pm 1.9 and 316.0 /pm 82.5 nmol per day per gram dry biomass, respectively). Senescing A. canescens, however, showed no measurable production. Therefore the tallgrass prairie provides regional sources of CH3Cl and CH3Br during the Amorpha spp. growing season (May-September). Rainfall manipulations showed that production rates continued to increase for up to 48 hours after wetting. Amorpha spp. showed the highest production rate of CH3Cl and CH3Br of any published values from grassland vegetation.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.A51C0119A
- Keywords:
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- 0322 Constituent sources and sinks;
- 0426 Biosphere/atmosphere interactions (0315);
- 0490 Trace gases