Hydraulic Properties and Ripening in Cultivated Acid Sulfate Soil Fields in Northern Europe

Acid sulfate (AS) soils cause severe environmental hazards in their recipient watercourses worldwide. Different soil water management practices can help prevent the hazards. Because long-lasting field experiments are expensive and site specific, sophisticated water flow simulation models can be used, for example, to estimate the effects of different management practices on the soil and runoff water quality. In AS soils, postglacial land uplift and the reclamation of soil for agricultural use have caused ripening of the soil. This study examined soil ripening and its effect on soil hydraulic properties, such as saturated hydraulic conductivity (K_sat), the water retention curve (WRC), macroporosity and air entry values, in different soil horizons of Nordic AS soils. The properties were determined from soil core samples in the laboratory, and single and dual-porosity models were fitted to the measured WRC data. The differences in WRCs at different depths were the result of the different ripening status of the soil horizons. The proportion of macroporosity was found to decrease with depth in the soil, and air entry values were higher in deep horizons than in the upper ripe horizons. According to the determined WRCs, the required soil water potential for the ripening of hypersulfidic parent sediments can be produced by plants only. The dual-porosity van Genuchten model provided a good fit to the measured data; the sensitivity of the model to its parameters varied between study sites due to the differences in underlying WRC measurements. In the long-term simulation of the development of water quality in AS soil areas, the effect of ripening on the evolution of soil hydraulic properties should be taken into account.