Chemical and Physical Changes in Tropical Soils from Seawater Exposure and Subsequent Rainwater Washes

There is little published information regarding the response of tropical island soils to periodic seawater intrusions. In this paper, we describe batch experiments where samples of three Hawaiian acidic upland soils (collected from western Oahu, Hawaii) were equilibrated for 16 h with simulated seawaters, ranging from 0.25-25 g L-1 (or ppT) of total salt, and then washed three times with 20 μS cm-1 solutions containing dilute concentration of NaCl (approx. 0.01 g.L-1) to simulate rainfall events. Solution data showed that the exchangeable sodium (ExNa) loads were high on all soils. While much of this ExNa was lixiviated with the rainwater washes, the soil exhibited significant remaining exchangeable sodium percentages (ESP). Consequences of the residual ESP after intensive washings were exhibited in the enhanced dispersiveness (i.e., increased settling time) of the soil colloids. In balance of the continuous sea spray and lower rainfall of the site, it is likely that high salt, high sodium effects would be manifested for extended periods of time in these soils.