The study of flow type dynamics at pedon scale via morphometric parameter analysis of dye-pattern profiles

The application of Brilliant Blue FCF tracer enables to identify flow types in multi-domain porous systems of soils via analyses of morphologic parameters of stained objects occurring in dye pattern profiles, as they represent the footprint of flow processes which occurred in soil during both the infiltration and the redistribution of dye solution. We analysed the vertical dye pattern profiles exposed for different time lengths, and revealed temporal evolution of dye solution redistribution leading to changes in flow types. The field experiment was performed with the Brilliant Blue tracer (the 10 g l⁻¹ concentration) applied on 1m x 1m surface of the Dystric Cambisol. The top litter horizon had been removed before 100 l of the tracer was applied. Four vertical profiles were excavated on the experimental plot (always 20 cm apart) at different times after the irrigation had been finished: 2 hours (CUT 2), 24 hours (CUT 24), 27 hours (CUT 27) and 504 hours (CUT 504). The analyses of the dyed patterns profiles showed the spatio-temporal changes in the dye coverage, surface area density, average BB concentration, and stained path width, which allowed us to specify three stages of dye solution redistribution history: (i) a stage of preferential macropore flow, (ii) a stage of strong interaction between macropore-domain and soil matrix leading to the generation of heterogeneous matrix flow and fingering flow types, and (iii) a final stage of dye redistribution within the soil body connected with leaching of BB caused by meteoric water. With increasing time, the macropore flow types convert to mostly matrix-dominated FTs in the upper part of the soil profile. These results were supported by soil hydrological modelling, which implied that more than 70% of the soil moisture profiles variability among CUT 2–CUT 504 could be explained by the time factor.