The effect of degree and duration of water saturation on selected redox indicators: pe, Fe2+ and Mn2+

Abstract

It was previously hypothesised that reduction in the soil will set in at 70% water saturation (S0.7). This study aimed to determine the effect of different degrees and durations of water saturation on reduction in soil. Reduction was measured as a decrease in soil oxidisability (pe) and an increase in soluble iron (Fe2+). A yellow brown apedal B horizon from profile 234 in the Weatherley catchment was used in this study. Soil cores were packed to a bulk density of 1.6 Mg m−3 and saturated to S0.6 (60% of the pores saturated with water), S0.7 (70% of the pores saturated with water), S0.8 (80% of the pores saturated with water), and S0.9 (90% of the pores saturated with water). Analyses started three days after water saturation. Samples were analysed every 3.5 days for the first three months and then once a week for another month. The experiment was terminated after 121 days. There was a good correlation between an increase in degree of water saturation and pe (R2=0.95), Mn2+ (R2=0.99) and Fe2+ (R2=0.99) concentration. The tendency was for pe, pH, Fe2+, and Mn2+ to remain relatively stable at S0.6 and to increase in variability as the water saturation increased, with most variability observed at S0.9. The change in redox activity took place between the S0.7 and S0.8 treatments. For this particular soil the highest rate of reduction took place in the S0.9 treatment.