Effects of temperature and soil moisture on methyl halide and chloroform fluxes from drained peatland pasture

A series of laboratory-based incubations using a stable isotope tracer technique was applied to measure the net and gross fluxes of CH3Cl and CH3Br as well as the net fluxes of CHCl3 from surface soils of the Sacramento-San Joaquin Delta of California. Annually averaged flux measurements show that these mineral/oxidized peat soils are a net source of CH3Cl (140 ± 266 nmol m−2 d−1) and CHCl3 (258 ± 288 nmol m−2 d−1), and a net sink of CH3Br (−2.3 ± 4.5 nmol m−2 d−1). Gross CH3Cl and CH3Br fluxes are strongly influenced by both soil moisture and temperature: gross production rates of CH3Cl and CH3Br are linearly correlated with temperature, whereas gross consumption rates exhibit Gaussian relationships with maximum consumption at soil moisture levels between 20 and 30% volumetric water content (VWC) and a temperature range of 25 to 35 °C. Although soil moisture and soil temperature strongly affect consumption rates, the range of gross consumption rates overall is limited (−506 ± 176 nmol m−2 d−1 for CH3Cl and −12 ± 4 nmol m−2 d−1 for CH3Br) and is similar to rates reported in previous studies. CHCl3 fluxes are not correlated with methyl halide fluxes, temperature, or soil moisture. The annual emission rates of CHCl3 from the Sacramento-San Joaquin Delta are found to be a potentially significant local source of this compound.