Abstract
AbstractUnderstanding nitrate migration through the deep vadose zone is essential for aquifer vulnerability assessments. The effect of variability of physical properties of the deep vadose zone on nitrate transport has been scarcely explored. Recently, deep nitrate storage profiles were determined in the vadose zone of the Loess Plateau of China. Using these observations along with measured soil properties, this study investigates the effect of loess vertical heterogeneity on water movement and nitrate transport through the deep vadose zone. Models of different complexity were established and calibrated. First, a simple piston flow and nitrate mass balance approach was calibrated to the observed nitrate storage. The results indicate that the total nitrate storage is estimated well, while the estimation of the distribution of nitrate is relatively poor. Subsequently, Richards' equation and the Advection‐Dispersion equation were evaluated. Three different conceptualizations of the numerical models were calibrated against deep vadose zone nitrate and water content observations: (1) one‐layer model assuming homogenous loess vadose zone; (2) a model that considers a hydraulic conductivity (Ks) decay function and (3) a model where the Miller‐Miller scaling factors are prescribed to account for changes of the hydraulic functions with depth. Accounting for the vertical Ks decay in the numerical models improved water flow performances. The study reveals the adequacy of implementing water flow and nitrate transport numerical models together with a simple representation of the vertical loess variability, for simulating nitrate migration in loess deep vadose zone environments.
Highlights
The excessive use and improper management of nitrate fertilization in agricultural production have led to nitrate groundwater and surface water contamination worldwide (Kapoor &Viraraghavan, 1997; Galloway et al, 2004)
Three different conceptualizations of the numerical models were calibrated against deep vadose zone nitrate and water content observations: (1) one-layer model assuming homogenous loess vadose zone; (2) a model that considers a hydraulic conductivity (Ks) decay function and (3) a model where the Miller-Miller scaling factors are prescribed to account for changes of the hydraulic functions with depth
Models of different complexity were implemented to describe the nitrate transport in four deep loess vadose zones of the Chinese Loess Plateau
Summary
The excessive use and improper management of nitrate fertilization in agricultural production have led to nitrate groundwater and surface water contamination worldwide (Kapoor &Viraraghavan, 1997; Galloway et al, 2004). Deep vadose zones exhibit large textural diversity and layering that can affect the flow and transport behavior (Nimmo et al, 2002; O’Geen et al, 2005; Onsoy et al, 2005). Implementation of such layering in models is challenging, as observations in the deep vadose zone are rare. O’Geen et al (2005) stated that in order to improve modeling performances for loess vadose zones, the relationships between hydrological processes and vertical variability needs to be evaluated
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
