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

摘要

A series of laboratory-based incubations using a stable isotope tracer technique was applied to measure the net and gross fluxes of CH _3Cl and CH _3Br as well as the net fluxes of CHCl _3 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 CH _3Cl (140 ± 266 nmol m ~(-2) d ~(-1)) and CHCl _3 (258 ± 288 nmol m ~(-2) d ~(-1)), and a net sink of CH _3Br (-2.3 ± 4.5 nmol m ~(-2) d ~(-1)). Gross CH _3Cl and CH _3Br fluxes are strongly influenced by both soil moisture and temperature: gross production rates of CH _3Cl and CH _3Br 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 CH _3Cl and -12 ± 4 nmol m ~(-2) d ~(-1) for CH _3Br) and is similar to rates reported in previous studies. CHCl _3 fluxes are not correlated with methyl halide fluxes, temperature, or soil moisture. The annual emission rates of CHCl _3 from the Sacramento-San Joaquin Delta are found to be a potentially significant local source of this compound.