Coupling of interfacial soil properties and bio-hydrological processes: The Flow Cell Concept

By applying the newly developed flow cell (FC) concept, this study investigated the impact of small-scale spatial variations (millimetre to centimetre) in organic matter (OM) composition (diffusive reflectance infrared Fourier transform spectroscopy), biological activity (zymography), and wettability (contact angle [CA]) on transport processes (tracer experiments, radiography). Experiments were conducted in five undisturbed soil slices (millimetre apart), consisting of a sandy matrix with an embedded loamy band. In the loamy band increased enzyme activities and OM (10 mm apart) were found compared with the sand matrix, with no interrelations although spatial autocorrelation ranges were up to 7 cm. CAs were increased (0–110°) above the loamy band and were negatively correlated with acid phosphatase. Missing correlations were probably attributed to texture variations between soil slices. A general correlation between CA and C content (bulk) were confirmed. Variability in texture and hydraulic properties led to the formation of heterogeneous flow patterns and probably to heterogeneously distributed interfacial properties. The new FC concept allows process evaluation on the millimetre scale to analyse spatial relations, that is, between small-scale textural changes on transport processes and biological responses. The concept has been proved as a versatile tool to analyse spatial distribution of biological and interfacial soil properties in conjunction with the analysis of complex micro-hydraulic processes for undisturbed soil samples. The concept may be improved by additional nondestructive imaging methods, which is especially challenging for the detection of small-scale textural changes.