Morphology of physical soil crusts and infiltration patterns in an artificial catchment

Hydraulic properties of the soil surface control the partitioning of rainfall between infiltration and runoff. For agricultural soils in humid climate regions, physical soil crusts have mostly been reported to reduce water infiltration. For initial soils developing in such climate on unstructured sediments without organic carbon, effects of soil crusting and slaking on infiltration was largely unknown. The objective was to compare initial soil and porous system formation with infiltration from three locations in a constructed hydrological catchment that has been left to undirected ecological succession for three years. We expected to find characteristic, mainly textural, effects of physical soil crusts during this initial stage of soil development. The three-dimensional (3D) micro-morphology was described using the X-ray computed tomography (CT); two-dimensional (2D) infiltration patterns were obtained from drip infiltration experiments using time-resolved neutron radiography (NT). Selected samples from three locations represent major sediment types of the catchment. The CT data indicated structural crusts on soil consisting of sandy to loamy sediments and depositional crusts on more sandy sediments. A combination of these two types developed at locations with silt to fine sand sediments; probably as a result of aeolian deposition on a structural crust. Moreover, isolated vesicle-shaped pores mostly reported from soils in arid environments were observed in most samples. The 2D infiltration patterns reflected the structural alteration by crusts only in samples containing silt and fine sand. Infiltrating water tended to pond within the aeolian deposits above the underlying structural crust. For all other samples, 2D infiltration pattern were relatively uniform; only negligibly small effect of structural crusts and vesicular pores on infiltration and redistribution could be observed in NR experiments although field measured infiltration rates were different. The relatively small differences in moisture patterns observed using NT suggest that the texture-related differences in physical soil crusts indicated by pore structure images using CT had only little effects on infiltration. The study improved understanding soil structure and water distribution relations in a hydrological catchment during initial ecosystem development.

► We visualized the effects of initial soil structure formation in an artificial hydrological catchment.
► Surface crusts developed with morphology according to substrate and development process.
► Neutron radiography showed infiltration patterns into the crusts.
► Vesicular pores could be found.