de Leeuw et al. (2000) measured aerosol mass produced from typical global surf zones (Section 2.4.2). Their measurements are relevant to the situation on King Island, as they were made at two sites on the surf coast of California, United States. Like the Californian coastline, the west coast of King Island is exposed to sea spray generated from the open ocean. de Leeuw et al. (2000) measured aerosol mass at several heights to 50 m, and at several distances from the surf zone. They estimated that between 17.7 - 32.6 kg m-2 yr-1
(study 1) and 9.4 - 27.1 kg m-2 yr-1 (study 2) was produced. The low rates are presumably
during calm conditions, the latter during storm conditions. They also concluded that at winds of 32 km hr-1 about 10 % of the finer sized particles of sea spray (defined as being
less than 10 µm in diameter) are deposited up to 25 km inland.
The median radius of sea spray containing sodium ions at Cape Grim, at the very north west tip of the Tasmanian mainland, is about 2 µm (Figure 44, Ayres et al. 1999). As
coast of King Island has the capacity to be transported across the entire width of the island, which is about 20 – 25 km wide.
By applying de Leeuw et al’s estimates at the western shoreline of King Island, which is about 40 km in length, a total of 200 ha of sea spray is generated between the surface of the ocean up to a height of 50 m ASL. Assuming uniform deposition from the surface of the ocean to a height of 50 m, this equates to between 35,400 - 65,200 tonnes yr-1 (study
1) and between 18,800 - 54,200 tonnes yr-1 (study 2) of aerosol mass. Using the arithmetic
mean of these estimates, between 27,100 - 59,700 tonnes of aerosol mass per year are predicted to be blown onto King Island from west coast generated sea spray.
0 20 40 60 80 100 120 140 0.01 0.1 1 10 Radius, µm S o d ium , nm ol e s m -3 Spring Summer Autumn Winter
Figure 44: The volume of sodium molecules contained within different sized sea spray during 2001 at Cape Grim on the Tasmanian mainland (Ayres et al. 1999).
An adaptation of the transport model used by de Leeuw et al. (2000) was used to predict the deposition of sea spray across King Island (Figure 45). The assumptions in the construction of Figure 45 were that 80 % of mass is deposited within the first 5 km of the surf zone, 50 % of the remaining mass is deposited between 5 and 15 km, 10 % of the remaining mass is deposited beyond 20 km, and no deposition occurs above 50 m ASL. The majority of the northern third of the island is susceptible to significant inputs of salt (Figure 45). It is assumed that the west coast dune system, some of which occurs
no recorded literature to support this assumption. The effect of the dunes of salt deposition is explored further in Section 6.4.5.
Currie 20 50 100 130 0 5000 10000 m N Contours (m ASL) 108 to 239 27 to 60 1.3 to 3
Estimated rates of aerosol deposition from west coast generated sea spray
(tonnes per hectare per year)
Sea spray generated aerosols (between 136 and 299 tonnes per vertical hectare per year between 0 and 50 m height above the surf zone)
Reedy Lake/Lake Flannigan
Egg Lagoon
Yellow Rock River basin
Figure 45: Rates of aerosol deposition from west coast generated sea spray following the findings of de Leeuw et al. (2000).
were classed as extremely-saline. In the Yellow Rock River basin, nine groundwater samples were assessed and the average conductivity was 10 dS/m. If it is assumed that:
• groundwater conductivity is entirely comprised of salt sourced only from sea spray;
• conductivity of 1 dS/m equates to 640 mg of salt per litre;
• groundwater within the Yellow Rock River basin is contained within a 2 m deep aquifer throughout the entire 7,500 ha basin;
• the density of groundwater is half that of free standing water; and,
• that only 5.4% of sea spray derived salt recharges the water table (Chiew and McMahon 1991), then;
the current level of groundwater salinity in the basin was deposited in just 19.8 to 43.9 years from sea spray alone.
Using the same assumptions for salt accumulation sourced only from rainfall (130 kg ha-1
yr-1 from 850 mm yr-1), groundwater conductivity in the basin can be accounted for over
a period of 9,117 years from rainfall alone.
From these examples it is clear that salts contained within sea spray aerosols are the major cause of salt deposition onto the island, particularly in the northern third. It is likely that fresher rainfall plays an important role in diluting and flushing these salts from the landscape. The implication of this dilution effect on sea spray additions of salt can be assessed in relation to predictions of climate change. Hennessy et al. (2006) predict that climate change may decrease the amount of rainfall falling in the area around King Island by a maximum of 3.5 % of 1990 levels by 2030, and evaporation may increase by a maximum of 5% of 1990 levels over this same period. By applying these estimates in the Yellow Rock River basin, and assuming additions from wind generated sea spray remain constant, between 0.14 and 0.225 tonnes ha-1 yr-1 (between 1,050 and 1,688 tonnes) of
salt will remain in the topsoil across the whole basin. This is about a 10 % increase in the amount of salt that is currently stored within the topsoil that was assessed in this study. Salt accumulation from rainfall has long been thought to be the primary source of salt deposition in Australia (Teakle and Burvill 1938; Cope 1958; Bettenay et al. 1964). However, no attempt has been made to distinguish the proportion of salt derived from
suggests that salt derived from sea spray alone is the major source of land based salinisation. It is likely to be the major source of salt accumulation within about 25 km from the Australian shoreline.
Compared to the accession rates from sea spray and rainfall, accessions from weathering is unlikely to comprise a significant component to the total salt budget for the island, confirming similar findings by Bettenay et al. (1964) and Dimmock et al. (1974). Should the current trend in climate change result in less rainfall and higher rates of evaporation, it is predicted that less salt will be flushed from the topsoil, compounding the detrimental affects of salinity.