Key Concerns: Quarry dusts, like dusts in general, affect vegetation by both physical and chemical processes. Physically, dust may cover the leaf surface and reduce the amount of light available for photosynthesis, or may occlude stomata. Occlusion may lead to increased resistance to gas exchange, or may prevent full stomatal closure, leading to water stress. Increased transpiration is a common response to dust exposure.
Chemically, quarry dusts may be relatively inert (from operations involving hard acidic rocks or some sandstones ) or may be strongly alkaline (limestone). Alkaline quarry dusts may have detrimental chemical effects on leaf surfaces. Infestation by pests and pathogens is likely to be enhanced.
Indirect effects may be caused through the soil, especially for the deposition of alkaline quarry dust on acid soils, which can increase the pH and available calcium, leading to changes in vegetation and invertebrate community composition. For unmanaged ecosystems which have been acidified by atmospheric deposition of sulphuric and nitric acids, there may be local beneficial effects if the quarry dust is alkaline, or can supply limiting minerals (e.g. calcium or magnesium). The subject has been reviewed by Farmer (1993).
Additional Comments:
Deposition rates for dusts are rarely measured, and exposure is judged by amounts retained on leaves. However, removal of dust from leaves by rain varies very greatly among plant species, from those that are 'self-cleaning' (the lotus effect) to those that accumulate large quantities (Neinhuis & Barthlott, 1997).
Deposition of dusts to aerodynamically 'rough' vegetation is greater than to short vegetation, which has led to the planting of trees and hedges as screens to intercept dust and protect areas close to sources (Freer-Smith et al., 1997).
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No estimate available |