With an assumed CCl4 emission rate of 39 Gg year−1, the best estimate of loss processes still underestimates the observed CCl4 (overestimates the decay) over the past 2 decades but to a smaller extent than previous studies. Changes to the rate of CCl4 loss processes, in line with known uncertainties, could bring the model into agreement with in situ surface and remote-sensing measurements, as could an increase in emissions to around 47 Gg year−1.
A large net emission of dimethyl sulfide (DMS) was observed during the growing season. During the non-growing dry season, small but quantifiable carbonyl sulfide (COS) exchange rates were correlated with soil temperature.
We calculate an updated partial lifetime of CCl4 with respect to the soil sink to be 375 (288–536) years, which is 50 to 90% longer than the most recently published best estimates of the soil sink partial lifetime (195 and 245 years).
Natural haloform emissions contribute to stratospheric ozone depletion but there are major unknown or underestimated sources of these gases. This study demonstrates that soil and water at tidal wetlands are important haloform sources, and emissions peak at the forest–marsh transition zone. The low-lying forested wetlands of the south-eastern United States that are facing sea-level rise and seawater intrusion may become hotspots for haloform emission.
Soils from a wheat field showed uptake of CO2 in dark and cool incubations, while showing emissions during either high termperatures or under light conditions. When soils were sterilized, only emissions of COS were observed. This suggests COS produciton is abiotic and facilitated by higher temperatures and/or light.