Coastal salt marshes as global methyl halide sources from determinations of intrinsic production by marsh plants

Emissions of CH 3 Cl, CH 3 Br and CH 3 I were measured biweekly for 12‐ to 24‐month periods between March 2002 and March 2005 from monospecific stands of four dominant southern California coastal salt marsh plants. These measurements revealed large inherent differences between species and more detailed patterns of seasonal production than previously reported. Marsh plants displayed intrinsic abilities to produce methyl halides. Salt marsh plants produced 92% of CH 3 Cl and 90% of CH 3 Br emitted and only 41% of the emitted CH 3 I. Unvegetated areas emitted 7.9% of CH 3 Cl, 9.9% CH 3 Br, and 59% of the emitted CH 3 I. The accuracy of the estimated methyl halide emissions from a coastal marsh and probably other ecosystems can be dramatically improved with increasing the number of species being measured and including emission from barren (mudflats and soil) areas. Estimates of global salt marsh emissions based on vegetated and barren area are 130, 21, 5.5 (mg m −2 yr −1 ) for CH 3 Cl, CH 3 Br, and CH 3 I, respectively, or 1.2, 3.9, and 0.8% of total global fluxes of these gases.