Cracks and Root Channels Promote Both Static and Dynamic Vertical Hydrological Connectivity in the Yellow River Delta

Vertical hydrological connectivity generally related heterogeneity of soil water and nutrient and the sustainability of vegetation restoration. Both the static and dynamic connectivity of soil have been studied for years, the relationship between them remains unclear, especially for coastal wetlands that greatly influenced by hydrological processes. In this study, static connectivity was defined as water flow paths and quantified by dye tracer experiment, whereas dynamic connectivity refers to the process of water movement and solute transport and described by solute penetration. Relationships between them were analyzed through the nonlinear fitting. Results showed that: 1) static connectivity was construed mainly by cracks in the upper soil layer and by root channels in the deeper soil, and these macropores led to heterogeneous distribution of water and solutes; 2) dynamic connectivity differed between soil columns, and non-equilibrium flow characterized by high infiltration rate and concentration in the initial phase was observed in soil with cracks and root channels; and 3) the static connectivity had significant effects on water movement while had no effects on solute transport. Infiltration rate decreased as dye coverage, fractal dimension, and the number of water pathway logistically increases. These findings highlight the importance of cracks and root channels on vertical hydrological connectivity in soil of S. salsa community, and suggest linking the static structure of water flow paths with soil water dynamic and heterogeneity to understand soil functions.