Water flow and multicomponent solute transport in drip‐irrigated lysimeters

Abstract

Controlled experiments and modeling are crucial components in the evaluation of the fate of water and solutes in environmental and agricultural research. Lysimeters are commonly used to determine water and solute balances and assist in making sustainable decisions with respect to soil reclamation, fertilization, or irrigation with low‐quality water. While models are cost‐effective tools for estimating and preventing environmental damage by agricultural activities, their value is highly dependent on the accuracy of their parameterization, often determined by calibration. The main objective of this study was to use measured major ion concentrations collected from drip‐irrigated lysimeters to calibrate the variably saturated water flow model HYDRUS (2D/3D) coupled with the reactive transport model UNSATCHEM. Irrigation alternated between desalinated and brackish waters. Lysimeter drainage and soil solution samples were collected for chemical analysis and used to calibrate the model. A second objective was to demonstrate the potential use of the calibrated model to evaluate lower boundary design options of lysimeters with respect to leaching fractions determined using drainage water fluxes, chloride concentrations, and overall salinity of drainage water, and exchangeable sodium percentage (ESP) in the profile. The model showed that, in the long term, leaching fractions calculated with electrical conductivity values would be affected by the lower boundary condition pressure head, while those calculated with chloride concentrations and water fluxes would not be affected. In addition, clear dissimilarities in ESP profiles were found between lysimeters with different lower boundary conditions, suggesting a potential influence on hydraulic conductivities and flow patterns.

Assessing salinity leaching efficiency in three soils by the HYDRUS-1D and -2D simulations

“…Furthermore, root uptake patterns and chemical factors such as precipitation and dissolution of calcite and gypsum in the root zone can cause an increase or decrease in EC sw in the root zone (Raviv and Lieth, 2007). Rainfall (Isidoro and Grattan, 2011) and drainage boundary conditions (Raij et al, 2016) can also influence the soil salinity distribution, as well as LF. Thus, LF under drip irrigation varies with soil water content, soil salinity, root distribution, and distance from and depth to the drip line.…”

“…They found that higher salinity accumulated on the edges of the wetted zone, and localized salt leaching around/ below the drip line occurred even under deficit irrigation. Raij et al (2016) used drip-irrigated lysimeter to calibrate the HYDRUS 2D/3D coupled with UNSATCHEM module and evaluated LFs using drainage water fluxes, chloride concentrations and overall salinity of the drainage water. Their results showed that, over the long term, LFs calculated from electrical conductivity (EC) were affected by the pressure head at the lower boundary conditions of the soil profile, while LFs calculated from chloride concentrations and drainage fluxes were not affected.…”

Soil salinization in very high-density olive orchards grown in southern Portugal: Current risks and possible trends

“…The standard solute transport module in HYDRUS considers the transport of one or multiple solutes, which can be either independent or involved in sequential first-order decay reactions (Hanson et al, 2008;Forkutsa et al, 2009;Roberts et al, 2009;Ramos et al, 2012). The major ion chemistry module adapted from the UNSATCHEM model (Šimůnek et al, 2016) allows for the simulation of multicomponent solute transport, describing the subsurface transport of multiple ions that may mutually interact, create various complex species, compete for sorption sites, and/or precipitate or dissolve (Gonçalves et al, 2006;Ramos et al, 2011;Rasouli et al, 2013;Raij et al, 2016). Finally, the HPx module (Jacques et al, 2018), in contrast to the previous module which is constrained to specific elements, offers users the flexibility to simulate multicomponent solute transport while defining their own species with particular chemical properties and reactions.…”

Geochemical Processes During Managed Aquifer Recharge With Desalinated Seawater

“…The simplified domain of two reactive layers reduces the Gapon selectivity coefficients that need to be optimized to four: and for each of the two model layers ( was not optimized because in all samples [K + ] < 0.04 meq L −1 , rendering cation exchange with K + negligible). The Gapon selectivity coefficients were inversely estimated with UNSATCHEM and the optimization code UCODE (Poeter et al, ), following Raij et al (). The optimized parameters in UCODE are obtained by minimizing iteratively the objective function (Hill, ): where is the objective function, is a vector of estimated parameters, n is the number of observations, is the weight for the i th observation, is the value of the i th observation, and is the simulated value which corresponds to the i th observation using the parameters .…”