Simulating Nitrate Leaching Profiles in a Highly Permeable Vadose Zone

Abstract

An approach is developed to simulate leaching of a dissolved chemical constituent in the vadose zone of an aquifer. Specifically, nitrate loading at the water table for different water table depths, for a range of aquifer permeability values, and for different cases of heterogeneity of the aquifer, are considered. Models from the literature are first used to derive soil-water characteristic curves (water retention and hydraulic conductivity) from a grain size distribution curve for unsaturated conditions. Given infiltration from the surface, the initial conditions for the chemical concentration, and the water content profile, leaching of the chemical in the vadose zone is simulated as a function of both time and depth. The methodology is illustrated for a permeable aquifer. Simulations are undertaken using a finite element code for saturated and unsaturated flow. Different scenarios are simulated depending on the heterogeneity of the aquifer and the depth of the water table. Modeling results show that in the example case studied, nitrate concentration loading at the water table does not depend strongly on the position of the water table, but rather on the material properties of the aquifer. The contribution of this endeavor resides in the methodology which allows a prediction of nitrate leaching using only the grain size property of the aquifer. It allows practitioners to obtain a first assessment of leaching with limited data.

Quantifying Nitrate Leaching under Commercial Red Raspberry Using Passive Capillary Wick Samplers

“…2c). It is commonly assumed that NO 3 –N leaching does not occur over the ASA during the summer because of the predicted soil water deficit (Table 1) (Chesnaux and Allen, 2008; Kowalenko, 1987). However, the measured NO 3 –N leached over summer in this study presents clear evidence that leaching can occur even during relatively dry summers, like the summer in Y2, which had a water deficit of 261 mm (not including irrigation) compared with 132 mm in the summer of Y1.…”

“…The postharvest residual NO 3 –N results suggest that the risk of NO 3 –N leaching can vary widely among commercial raspberry fields, likely in response to variations in management practices and soil properties, and may also vary significantly within individual fields (Zebarth et al, 2002, 2015). Although researchers commonly assume NO 3 –N leaching occurs predominantly during the rainy non‐growing season (Chesnaux and Allen, 2008; Zebarth et al, 2015), evidence of NO 3 –N leaching from the root zone during the growing season was found in some raspberry fields and years (Zebarth et al, 2007). This suggests that postharvest residual NO 3 –N may underestimate the risk of NO 3 –N leaching in some cases.…”

The atmospheric transport of iodine‐129 from Fukushima to British Columbia, Canada and its deposition and transport into groundwater

“…The hydraulic properties of the ASA have been studied in the context of nitrate leaching and transport as the primary land use in the region is agriculture with a high density of berry farming (raspberries and blueberries), poultry production and some dairy farms [ Wassenaar , ; Cox and Kahle , ; Wassenaar et al ., ; Chesnaux et al ., ]. NO 3 contamination throughout much of the aquifer is attributed to the intensive nature of agricultural activities in this area [ Hii et al ., ; Chesnaux and Allen , ; Zebarth et al ., ].…”

Predicting Nitrate Concentration and Its Spatial Distribution in Groundwater Resources Using Support Vector Machines (SVMs) Model

“…Among pollution sources, agricultural activities are well known as nonpoint sources of pollution. Nitrate contamination of aquifers is a significant problem in many agricultural areas [6]. Nitrate is the primary form of nitrogen in natural waters [7].…”