Leaf cutter ants: a possible missing source of biogenic halocarbons

Abstract

Environmental context. With large reductions in anthropogenic emissions of many ozone-depleting gases in response to the Montreal Protocol, gases with biogenic sources have become relatively more important in recent years. The global budgets of the biogenic halocarbons are unbalanced with known sinks outweighing sources, suggesting that additional natural sources are required to balance the budgets. In the present study, an investigation has been carried out to determine the importance of leaf cutter ants as a missing source of the biogenic halocarbons, which will reduce the discrepancy of the global budget of the halocarbons. Abstract. Leaf cutter ant colonies are shown to be a potentially significant new source of biogenic halocarbons. Fungus cultivated by these ant species may emit CH3Br, CH3I, CH3Cl, CH2Cl2 and CHCl3 in significant quantities, contributing to their respective global atmospheric budgets. The study suggests that the mixing ratios of CH3Br, CH3I, CH3Cl, CH2Cl2 and CHCl3 in the ant colony under test were significantly higher than background levels, by on average a factor of 1.5–5.0. Sampling was carried out during three stages of ant colony development (new, moderately active and highly active) and it was found that levels of these halocarbons were elevated during the active phases of the ant colony life cycle. A very rough estimate of the possible emission of CH3Br, CH3I, CH3Cl, CH2Cl2 and CHCl3 from ant colonies globally are 0.50, 0.02, 0.80, 0.15 and 0.22 Gg year–1.

Halogen biogeochemistry of invasive perennial pepperweed (Lepidium latifolium) in a peatland pasture

“…[3] Due to the diversity of biogenic sources, the quantification of methyl halide contribution from these sources is challenging. Known terrestrial sources include coastal salt marshes [Drewer et al, 2006;Manley et al, 2006;Rhew et al, 2000], mangroves [Manley et al, 2007], freshwater wetlands [Dimmer et al, 2001;Varner et al, 1999], woodland and forest soils [Drewer et al, 2008;Varner et al, 2003], and fungi [Mead et al, 2008;Redeker et al, 2004a]. Specific plants are potentially large emitters of methyl halides, including agricultural crops such as rapeseed (Brassica napus), cabbage (Brassica oleracea), rice (Oryza sativa), and potato tubers (Solanum tuberosum) [Gan et al, 1998;Harper et al, 1999;Redeker et al, 2000;2002;Khan et al, 2011;Saini et al, 1995].…”

Methyl chloride from the Aura Microwave Limb Sounder: First global climatology and assessment of variability in the upper troposphere and stratosphere

“…Warm tropical and subtropical open ocean and coastal waters, once thought to be the dominant source [e.g., Singh et al, 1983], are now estimated to contribute 11% to the global CH 3 Cl budget [e.g., Moore et al, 1996;Hu et al, 2010;Xiao et al, 2010]. Other minor sources include freshwater wetlands, peatbogs, coastal salt marshes, and mangroves [e.g., Varner et al, 1999;Rhew et al, 2000;Rhew and Mazéas, 2010;Dimmer et al, 2001;Manley et al, 2007;Hardacre et al, 2009]; flooded rice paddies [Redeker et al, 2000;Redeker and Cicerone, 2004]; wood-rotting fungi [Harper, 1985;Watling and Harper, 1998;Moore et al, 2005]; and fungus gardens cultivated by leaf cutter ants [Mead et al, 2008]. Atmospheric CH 3 Cl also arises through abiotic release from senescent and dead plant material and organic matter in soils and sediments (again primarily in tropical and subtropical regions) [e.g., Keppler et al, 2000Keppler et al, , 2005Hamilton et al, 2003].…”

Bromoform in the tropical boundary layer of the Maritime Continent during OP3

“…Secondly, there is some evidence that the rainforest might be a direct source of some halocarbons. A number of studies have looked at possible biogenic sources of halocarbons (principally CH 3 Cl, but including other chloro-and bromocarbons), with the sources including plants, leaf litter, wood-rotting fungi and insects (Harper,et al, 2008;Mead et al, 2008;Saito et al, 2008). Thirdly, there is increasing interest in the role of natural, short-lived halogen species, which could potentially be lifted rapidly to the low stratosphere in deep convection where they could play a role in stratospheric ozone destruction (see, for example, Law et al, 2007).…”