A study of the interactions between salinity, soil erosion, and pollutant transport on three Queensland soils

Abstract

The effects of salinity and sodicity on soil erosion, sediment transport, and runoff water quality were studied under the simulated rainfall using 3 soils whose salinity and sodicity were artificially raised. Soil type and salt treatment both affected sediment loss, with a significant interaction between the 2 factors. The salt treatment decreased aggregate stability, reduced aggregate mean weight diameters, and increased sediment loss for all soils, but the soil with the most stable aggregates (Redlands) showed the highest impact. The initial treatment resulted in a sharp rise in the electrical conductivity (EC) and exchangeable sodium percentage (ESP) of all 3 soils but these increases were much higher in the sandy Toohey soil than the 2 clay soils. Electrical conductivities of all 3 treated soils decreased during the rainfall events, but the Toohey soil showed the largest decrease. The ESP of the treated Toohey soil decreased rapidly during the rainfall event due to its coarse texture, rapid renewal of its pore water, and the accessibility of its exchange sites by ions in the solution. The EC of the treated Redlands clay was reduced and its ESP increased during the rainfall events, which resulted in the weakening of its stable aggregates and increased erosion. Sodium adsorption ratio and EC of runoff water from treated soils decreased rapidly with rainfall duration for all 3 soils, but runoff from Toohey showed the largest decrease. The interaction between increased salinity-sodicity and erosion thus appears to be heavily dependent on soil texture, degree of aggregation, and aggregate stability, the 3 determinant factors for soil porosity and pore-size distribution. The results indicate that large sediment and salt losses can occur in runoff from saline-sodic soils, even at low slopes and from apparently stable soils, with major downstream water quality consequences.