Methyl chloride isotopic signatures from Irish forest soils and a comparison between abiotic and biogenic methyl halide soil fluxes

Kelly R. Redeker, Robert M. Kalin

Research output: Contribution to journalArticle

10 Citations (Scopus)

Abstract

Forest soils demonstrate in a microcosm the difficulties that are faced in quantifying methyl halide budgets. Carbon isotopic analyses have been proposed as a potential tool to address these concerns and in this study we have measured significant enrichment of the methyl chloride 13C/12C isotopic ratio (from -40.2 +/- 0.8 parts per thousand to -33.4 +/- 7.4 parts per thousand) after 9 min chamber emplacement on local Irish forest soils. This enrichment occurred independent of direction of methyl chloride fluxes. Measurements from soil cores in a flow-through system (FTS) are comparable with chamber-based isotopic measurements and indicate that methyl chloride produced abiotically from organic soil horizons has an isotopic 13C signature of -53 +/- 49 parts per thousand, significantly less depleted than previously reported. Average net methyl chloride, methyl bromide and methyl iodide fluxes from soils (77.8 +/- 2.1, 1.25 +/- 3.63 and 0.35 +/- 2.00 mu g MeX m-2 day-1, respectively) are in line with previously reported values; however, a better understanding of spatial and temporal variability is needed for budget quantification. Methyl halide fluxes from FTS soil cores demonstrate that, on a per gram basis, most consumption occurs through biologically driven processes in the O horizon, with progressively smaller contributions in deeper horizons. Sporadic biogenic production was observed in shallow soil horizons only. Abiotic production was at most one-tenth the net biological reaction rate in the O horizon and did not appear to be significantly different from zero in lower horizons. Modelled emissions based upon observed and reported rates for production, consumption and diffusion within the soil atmosphere system are unable to replicate all observed isotopic signatures from chamber fluxes.

LanguageEnglish
Pages1453-1467
Number of pages15
JournalGlobal Change Biology
Volume18
Issue number4
DOIs
Publication statusPublished - Apr 2012

Fingerprint

Methyl Chloride
methyl chloride
halide
forest soil
Fluxes
Soils
soil horizon
soil
flux chamber
methyl bromide
shallow soil
iodide
isotopic ratio
organic soil
microcosm
reaction rate
emplacement
comparison
atmosphere
carbon

Keywords

  • isotopic
  • methyl bromide
  • methyl chloride
  • soils
  • trace gas fluxes

Cite this

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Methyl chloride isotopic signatures from Irish forest soils and a comparison between abiotic and biogenic methyl halide soil fluxes. / Redeker, Kelly R.; Kalin, Robert M.

In: Global Change Biology, Vol. 18, No. 4, 04.2012, p. 1453-1467.

Research output: Contribution to journalArticle

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AU - Redeker, Kelly R.

AU - Kalin, Robert M.

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AB - Forest soils demonstrate in a microcosm the difficulties that are faced in quantifying methyl halide budgets. Carbon isotopic analyses have been proposed as a potential tool to address these concerns and in this study we have measured significant enrichment of the methyl chloride 13C/12C isotopic ratio (from -40.2 +/- 0.8 parts per thousand to -33.4 +/- 7.4 parts per thousand) after 9 min chamber emplacement on local Irish forest soils. This enrichment occurred independent of direction of methyl chloride fluxes. Measurements from soil cores in a flow-through system (FTS) are comparable with chamber-based isotopic measurements and indicate that methyl chloride produced abiotically from organic soil horizons has an isotopic 13C signature of -53 +/- 49 parts per thousand, significantly less depleted than previously reported. Average net methyl chloride, methyl bromide and methyl iodide fluxes from soils (77.8 +/- 2.1, 1.25 +/- 3.63 and 0.35 +/- 2.00 mu g MeX m-2 day-1, respectively) are in line with previously reported values; however, a better understanding of spatial and temporal variability is needed for budget quantification. Methyl halide fluxes from FTS soil cores demonstrate that, on a per gram basis, most consumption occurs through biologically driven processes in the O horizon, with progressively smaller contributions in deeper horizons. Sporadic biogenic production was observed in shallow soil horizons only. Abiotic production was at most one-tenth the net biological reaction rate in the O horizon and did not appear to be significantly different from zero in lower horizons. Modelled emissions based upon observed and reported rates for production, consumption and diffusion within the soil atmosphere system are unable to replicate all observed isotopic signatures from chamber fluxes.

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