Salt impaction at near-coastal locations and possible effects on grapevines in southwest of Western Australia

Abstract

Damage to grapevines at Margaret River prompted a study of the salt in rainfall and the potential for salt impaction on vegetation. Concentrations of salt in rain varied seasonally, with values to 250 mg C11 −1 and average values of 10 mg C11 −1. Rainwater with the highest salt concentrations drying on vine leaves was estimated to yield salt loads os 32 mg C1 m −2. Visual damage was observed with salt loads of an order of magnitude higher than this. Salt impaction increased with wind strength. During periods when onshore winds were strong (> 10 m s −1), rates of impaction measured in dust gauges ranged up to 400 mg Cl m −2 day −1 with mean annual rates of impaction ranging from 12.1 to 26.1 mg Cl m −2 day −1. Newly emergent leaves, because they are smaller than the dust gauges used to monitor impaction, can collect approximately three times more salt. Consideration of the values obtained for impaction suggest that, in the absence of rain, salt could accumulate over periods of 7 days to levels known to cause damage. Because of the highly significant correlation between strong winds and high salt impaction, it was not possible to attribute the observed damage to either of these factors alone. Previous workers have found that physical damage to leaves by strong winds increases the sensitivity of vines to salt. Wind and salt damage is a greater risk in the Margaret River area than elsewhere in the southwest of Western Australia because of the frequent occurrence of gale-force winds. Gales, with high values of impaction, are not usually associated with rain-free periods, but when these conditions occur, vine damage is likely to be particularly severe at exposed sites.