Saturated hydraulic conductivity of sulfuric horizons in coastal floodplain acid sulfate soils: Variability and implications

Abstract

The saturated hydraulic conductivity ( K s) of sulfuric horizons exerts a fundamental control on the connectivity between shallow groundwater and drains in coastal acid sulfate soils (CASS), strongly influencing rates of lateral seepage towards or from field drains. The K s of sulfuric horizons was assessed on seven major coastal floodplains of eastern Australia using an in situ recovery technique conducted in ~ 0.4–0.65 m deep pits. Duplicate recovery tests were conducted in a total of 148 pits located in 32 separate geomorphic units across the seven coastal floodplains. Most pits were constructed in clay soils with acidic (pH < 4.0) shallow groundwater. The K s spanned four orders of magnitude, ranging from < 0.5 m day − 1 to > 500 m day − 1 . Data are log normally distributed and the median K s was ~ 15.4 m day − 1 . Over 40% of the pits had values > 20 m day − 1 , challenging the assumption that K s in sulfuric horizons in CASS landscapes is generally low. Visual observations confirm that high K s values were strongly associated with macropore flow. These data demonstrate that K s in coastal floodplain sulfuric horizons can be very high and is extremely variable within individual floodplains. These findings highlight the need for site specific assessments of soil hydraulic properties in CASS in order to ensure appropriate design and application of acid management techniques.