Soil water repellency and chemical soil properties in a beech forest soil — Spatial variability and interrelations

• Spatial variability of acidity indicators was analyzed in a beech forest soil.
• Stemflow infiltration caused spatial oscillation of soil acidity.
• Soil acidity increased soil water repellency (SWR).
• Particle surface properties (O/C ratio, nonpolar C) correlated to SWR.
• Chemical soil quality was related to SWR.

Higher solute input due to stemflow infiltration causes enhanced soil acidification near the tree base. Infiltration-driven alteration of chemical soil properties like pH, and carbon to nitrogen ratio (C/N) and particle surface properties like oxygen to carbon ratio (O/C), may also affect soil wettability with a trend to increased soil water repellency (SWR) with increased acidity. Our study provides a link between chemical soil quality and physical behavior with respect to soil water infiltration and SWR, respectively in a beech forest soil.The spatial variability of soil properties was analyzed within a grid (Δ = 1 m, 5 m × 8 m = 40 m2) and, to reveal direct effects of stemflow influence on soil properties, we sampled along a tree row (Δz = 0.8 m, l = 46.60 m) with varying sampling points to tree distances. All samples were taken in a beech (Fagus sylvatica L.) forest Bws/Bw-horizon in 0.1–0.2 m depth (dystric cambisol).Analysis of spatial variability by standard statistics and geostatistical methods revealed no substantial differences between grid and transect samples for pH and sulfate, Al, and Fe (aluminum and iron oxalic acid extractable) concentration and SWR in terms of contact angle (CA, sessile drop method) measured for bulk soil samples. According to standard statistics, the total variance of chemical soil properties and SWR was independent of stemflow infiltration pattern. Results of spectral variance analysis showed that the spatial variability of acidification (pH, Al content) as well as SWR was strongly affected by the pattern of patches with and without stemflow infiltration or the distribution of beech trees, respectively. In a more or less regularly planted beech forest this caused a cyclic variation of soil acidification and SWR with a strong trend to increased SWR (CA ranges 17°–72°) with increased soil acidity. Specific chemical surface properties, analyzed via X-ray photoelectron spectroscopy, like O/C ratio (r2 = 0.782) and the amount of nonpolar C species (r2 = 0.768) as well as surface Al concentration (r2 = 0.867) clearly showed a strong relation to CAs. Hence, SWR was strongly affected by stemflow infiltration patterns into soil. For C/N, sulfate, and Fe content no significant relations to SWR or soil acidity were found.