A Physically Based Model for Preferential Water Flow and Solute Transport in Drained Agricultural Fields

Abstract

Consequently, some of the agrochemicals can bypass the soil matrix and its capacity to store, absorb, and transform the solute. Thus, agrochemicals and nutrients can be carried to great depths, where degradation is limited (Boesten et al., 2000), possibly increasing the total amounts leached to groundwater. The preferential processes usually take place in what is often called macropores (Beven and Germann, 1982, 2013; Jarvis, 2007). In the literature, the term macropores is arbitrarily used for soil structural components like cracks, fissures, root channels, and earthworm borrows (Beven and German, 1982, 2013). These generally occur in soils with well-developed structures, that is, soils with silt or clay texture (Beven, 2018; Jarvis, 2007). Jarvis (2007) distinguishes between biologically induced macropores (e.g., root channels and earthworm borrows) termed biopores and macropores as a result of soil aggregation (e.g., fissures and cracks). In this work, the term biopores will be used to describe root channels, and earthworm borrows in which capillary effects are negligible. Artificial drainage is a common agricultural practice, which allows a field to be cultivated and increases crop production, but simultaneously can create new pathways for leaching of nutrients and agrochemicals to surface water (

Modeling Preferential Water Flow and Pesticide Leaching to Drainpipes: The Effect of Drain‐Connecting and Matrix‐Terminating Biopores

“…The drain‐connecting biopores, as implemented in Daisy, have an unlimited capacity to transport water and solute to the drainpipes (Holbak et al., 2021). Specifically, when water enters the drain connected biopores in Daisy, it is instantaneously removed from the system, since drains are currently assumed to have an infinite capacity for removing soil water.…”

“…Water flow over the biopore‐matrix interface is activated when the soil water pressure in the matrix is at or very close to saturation. Water flow from the matrix to biopores continues until the pressure head in the soil matrix drops below the termination threshold, $${h}_{\text{term}}$$ (Holbak et al., 2021). For drain‐connecting biopores, water is instantaneously moved to the drainpipe, representing an infinite capacity system.…”

“…Water flow between matrix and biopores is described for classes of biopores, with the same physical properties (start depth, $${Z}_{\text{top}}^{b}$$ [ L ], end depth, $${Z}_{\text{end}}^{b}$$ [ L ], radius, $${r}_{b}$$ [ L ] and whether they are drain‐connecting or matrix‐terminating) (Holbak et al., 2021): $$${{\Gamma}}_{\text{BF}}^{{\text{BC}}_{i}}=\frac{4\pi {D}_{b}{K}_{xx}(h)\left({h}^{b}(z)-h(z)\right)}{\mathrm{ln}\left({D}_{b}(x)\pi {r}_{b}^{2}\right)}$$$ where $${\text{BC}}_{i}$$ is the i th biopore class, $${D}_{b}(x)$$ [ L −2 ] is the biopore density in the horizontal plane, $${h}^{b}$$ [ L ] is the pressure head in the biopores at depth z [ L ], and $${r}_{b}$$ [ L ] is the biopore radius. For drain‐connecting biopores, $${h}^{b}$$ is a function of distance to the drains and for matrix‐terminating biopores $${h}^{b}$$ is a function of the water level in the biopores (Holbak et al., 2021). The pressure head distribution, $${h}^{b}(z)$$…”

“…where 𝐴𝐴 BC𝑖𝑖 is the ith biopore class, 𝐴𝐴 𝐴𝐴𝑏𝑏(𝑥𝑥) [L −2 ] is the biopore density in the horizontal plane, 𝐴𝐴 𝐴 𝑏𝑏 [L] is the pressure head in the biopores at depth z [L], and 𝐴𝐴 𝐴𝐴𝑏𝑏 [L] is the biopore radius. For drain-connecting biopores, 𝐴𝐴 𝐴 𝑏𝑏 is a function of distance to the drains and for matrix-terminating biopores 𝐴𝐴 𝐴 𝑏𝑏 is a function of the water level in the biopores (Holbak et al, 2021). The pressure head distribution, 𝐴𝐴 𝐴 𝑏𝑏 (𝑧𝑧) , inside the biopore is assumed to be in hydrostatic equilibrium.…”

Effects of influent concentration and different valence cations on solute preferential transport in inter-tidal zone of Yellow River Estuary

“…Among them, the accumulation of nitrate nitrogen is the largest and exists in the form of non-adsorbable solute. A study has found that the vertical transport of agrochemicals in cultivated land and arid soil was affected by bio-pores under saturated conditions, which connecting the soil surface directly with the drainpipes [5] . However, the effects of influent concentration and soil cation valence on preferential transport of nitrate in intertidal sediments with bio-pores under the coastal zone are still not well-understood.…”