Concept to quantify the effects of SOM on water retention hysteresis and hydrophobicity in sandy soils and their implication for soil water modeling

Global warming is promoting extreme weather conditions like more frequent heavy rainfall events and longer periods of drought in central Europe. This can lead to an increase in hydrophobicity and hysteretic behavior of soils, potentially reducing its water retention capabilities and changing the soil water balance. These soil characteristics are also highly dependent on the amount and properties of soil organic matter (SOM). Climate change effects are expected to be particularly pronounced in sandy soils, which have comparatively low water retention capacities.

In this study, we will quantify the effects of SOM on soil hydraulic properties and analyze their impact on the soil water balance in hydrological models in comparison to data acquired by pedotransfer functions.

To cover a wide range of SOM content and properties, we sampled sandy soils (> 80% sand) from five different land use categories (arable land, heathland, grassland, deciduous and coniferous forest). The samples were taken in the Southwest of the Metropolitan region of Hamburg, near Lüchow-Dannenberg. The samples were analyzed for their total soil organic carbon and nitrogen content, and will further be analyzed for their fractions of particulate organic matter (POM) and mineral associated organic matter (MAOM). Hydrophobicity was determined using the water-drop-penetration-time test and contact angle measurements with the sessile drop method. Furthermore, the Integrative Repellency Dynamic Index (IRDI) will be determined for all topsoils to quantify the average hydrophobicity of the sample. Soil water retention is acquired using the porous plate method as well as the evaporation method (HYPROP), including wetting and drying curves. This data will serve as a starting point for simulations under different climate scenarios using HYDRUS.

The aim of this study is to improve our understanding on how hydrophobicity and water retention (wetting and drying) in sandy soils are influenced by the content and properties of SOM, and how this affects the results of hydrological models under different climate scenarios. This will contribute to improve the ability to assess future soil water dynamics, which is vital for sustainable land use and climate change adaptation.

 

The study is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany‘s Excellence Strategy – EXC 2037 'CLICCS - Climate, Climatic Change, and Society' – Project Number: 390683824, contribution to the Center for Earth System Research and Sustainability (CEN) of Universität Hamburg".