Soil Water Repellency and its Impact on Hydraulic Characteristics in a Beech Forest under Simulated Climate Change

Abstract

Core Ideas Rainfall redistribution increased soil water repellency in a beech forest soil Soil water repellency correlated with organic matter composition and C/N ratio Contact angles correlated with air‐entry value of hydraulic soil characteristics Climate change is expected to result in prolonged dry periods and an increased occurrence of extreme rainfall events that can increase soil water repellency (SWR). However, this relationship has not been studied under field conditions yet. Also, for the development of hydrological models accounting for SWR, dependencies between SWR and soil hydraulic characteristics would be required. Our hypotheses were that (i) prolonged dry periods increase SWR by changing the composition of the soil organic matter (SOM) and that (ii) SWR alters hydraulic soil properties by the air‐entry value. The objective of the study was to assess the impact of different rainfall redistributions on the degree of SWR, physicochemical soil characteristics, and soil hydraulic properties. A field experiment was conducted on a Podsolic Cambisol in a beech forest with plots covered by roofs and irrigated artificially. Two rainfall redistribution treatments (moderate and extreme) and control plots were compared after two vegetation periods. Potential SWR was characterized by the soil–water contact angle, while the actual degree of SWR was derived indirectly from infiltration experiments with water and ethanol. We found an increase in SWR due to rainfall redistribution. Contact angles correlated positively with the contents of organic carbon (OC) and nitrogen and the relative amount of hydrophobic groups in the organic matter and negatively with the C/N ratio. Differences between intrinsic and actual hydraulic properties increased with prolonged dry periods. Contact angles correlated with the air‐entry value (inverse of van Genuchten parameter α). This finding offers a way to account for SWR in hydraulic models.