Investigation into preferential flow in natural unsaturated soils with field multiple-tracer infiltration experiments and the active region model

Roots‐Enhanced Preferential Flows in Deciduous and Coniferous Forest Soils Revealed by Dual‐Tracer Experiments

“…The dual‐tracer experiment was performed at each plot to simultaneously characterize the preferential flow patterns and solute transport, similar to earlier studies (Nobles et al, 2010; Schwen et al, 2014; Sheng et al, 2014). Both tracers have advantages and disadvantages.…”

“…It can also approximate the movement of organic molecules as its charge and aromatic characteristics approximately resemble other organic molecules (Nobles et al, 2010; Wang and Zhang, 2011). Conversely, the low background concentration and nonreactive nature of the anion Br − in soils make it highly suitable for tracing the flow of water and negatively charged nutrient ions in field studies (Flury and Wai, 2003; Sheng et al, 2014). But it often requires extensive soil or water sampling and analyses to identify the preferential flow paths.…”

“…To measure the Br − concentrations, 10 g of each soil sample was equilibrated with 50 mL deionized water by shaking for 12 h, followed by centrifugation at 3000 rpm for 1 h. The supernatant was then filtrated using a qualitative filter paper. The Br − concentration in the filtrate was measured by an ion meter (PXSJ‐216F, Shanghai INESA & Scientific Instrument Co., Ltd.) (Sheng et al, 2014; Zhang et al, 2015). Then the concentrations of BB and Br − in soil samples were calculated as the tracer mass per unit mass of soil (mg kg −1 soil).…”

“…Although macropores only contribute a small portion to total soil porosity, they play a pivotal role in preferential flow (Wilson and Luxmoore, 1988; Moret and Arrúe, 2007). They are mainly formed by earthworm burrows, root channels, soil shrinkage cracking, chemical weathering, or freezing–thawing cycles and typically have large pore size (>75 μm) and continuity that facilitate the preferential transport of water and solutes (Beven and Germann, 1982; Sheng et al, 2014; Liu and Lennartz, 2015). Both living and decayed roots could serve as preferential flow paths, and root exudates could enhance soil aggregation and subsequently the formation of inter‐aggregate macropores (Fageria and Stone, 2006; Ghestem et al, 2011; Vannoppen et al, 2015).…”

Characteristics of the surface–subsurface flow generation and sediment yield to the rainfall regime and land-cover by long-term in-situ observation in the red soil region, Southern China

“…The lower subsurface flow on bare land was typically attributed to soil compaction by raindrops and an increased in the bulk density of the topsoil with time (Cassel et al, 1995;Truman et al, 2005). Rotted litter and roots loosened the topsoil and provided pathway for the formation of preferred flow, which was the most important component of the subsurface flow (Kramers et al, 2009;Fu et al, 2012;Zhang et al, 2014;Sheng et al, 2014).…”