Production of bromoform and dibromomethane by Giant Kelp: Factors affecting release and comparison to anthropogenic bromine sources

Macrocystis pyrifera (Giant Kelp), a dominant macroalgal species in southern California, produced I71 ng per g fresh wt (gfwt) per day of CHBr, and 48 ng gfwt-' d-' of CH,Br, during laboratory incubations of whole blades. Comparable rates were measured during in situ incubations 01 intact fronds. Release of CHBr, and CH,Br, by M. pyr$eru was affected by light and algal photosynthetic activity, suggesting that environmental factors influencing kelp physiology can affect halomethane release to the atmosphere. Data from H,O, additions suggest that brominated methane production during darkness is limited by bromide oxidant supply. A bromine budget constructed for a region of southern California indicated that bromine emitted from the use of CH,Br as a fumigant (1 X 1 Ox g BI yr -I) dominates macroalgal sources (3 X 10" g Br yr-I). Global projections, however, suggest that combined emissions of marine algae (including microalgac) contribute substantial amounts of bromine to the global cycle, perhaps on the same order of magnitude as anthropogenic sources.