The effects of iron ore dust on mangroves in Western Australia: Lack of evidence for stomatal damage

Abstract

Anecdotal evidence suggests that iron ore dust derived from industrialshiploading activities in north-western Australia may be more injurious tomangroves than is naturally-derived dust, because of its more angularstructure and presumed ability to damage stomatal cells. Abaxial hairs onthe most common mangrove, Avicennia marina (Forfk). Vierh., havebeen thought to exacerbate this effect through trapping and retaining dust.This study examined this hypothesis. Leaves were collected from dustyindustrial areas and natural environments. Leaves in dusty environmentswere chosen on the basis of their thick coating of iron ore dust on both leafsurfaces. Approximately 3,000 stomata were examined in detail using lightmicroscopy. Hair density, stomatal aperture, cell condition and presence ofdust were also noted. Despite there often being a visible layer of dust onthe abaxial and adaxial surfaces of the leaf, evidence for dust of any kindwithin stomatal spaces was noted, in total, only three times. The lack ofvisible dust in stomata was attributed to three factors; the density andmorphology of the abaxial hairs, which prevent dust from enteringthe space between the hairs, and the improbability of dust circulating in thestagnant air within that space and moving against gravity past the guardcells. It was concluded that if iron ore dust affects mangroves, it must doso by some other mechanism, such as either increased temperature, shadingor a restriction of transpiration by the thickness of the dust on the abaxialsurface.