Abstract
Nitrogen-nitrate, while being fundamental for crop production, is of particular concern in the agricultural sector, as it can easily leach to the water table, worsening groundwater quality. Numerical models and Geographic Information System may support the estimation of nitrate leaching rates in space and time, to support sustainable agricultural management practices. In this paper, we present a module for the simulation of the processes involved in the nitrogen cycle in the unsaturated zone, including nitrate leaching. This module was developed taking steps from the ANIMO and EPIC model frameworks and coupled to the hydrological models integrated within the FREEWAT platform. As such, the nitrogen cycle module was then included in the FREEWAT platform. The developed module and the coupling approach were tested using a simple synthetic application, where we simulated nitrate leaching through the unsaturated zone for a sunflower crop irrigated district during a dry year. The results of the simulation allow the estimation of daily nitrate concentration values at the water table. These spatially distributed values may then be further used as input concentration in models for simulating solute transport in aquifers.
Highlights
Nitrogen-nitrate, while being fundamental for crop production, is of particular concern in the agricultural sector, as it can leach to the water table, worsening groundwater quality
Data coming from experimental activities about daily concentration of NO3− arriving at the water table are not published yet—and because of this it was not possible to validate the simulated values
Nitrate is of particular concern, as it is conservative and it may rapidly leach to the water table, causing high, or even exceeding, according to ongoing regulations, concentrations in aquifers and, potential negative effects on the environment and even human health, in case groundwater is used for drinking purposes
Summary
Nitrogen-nitrate, while being fundamental for crop production, is of particular concern in the agricultural sector, as it can leach to the water table, worsening groundwater quality. Nitrate pollution of water is a major issue worldwide (Mateo-Sagasta et al, 2018; Wang and Li 2019; Zhang et al, 2019) [1–3]. It originates mostly from the use of inorganic fertilizers and animal manure in agricultural areas (Liao et al, 2012; Nakagawa et al, 2017; Ward et al, 2018; Zhang et al, 2018a) [4–7], and inefficient management of treated/untreated wastewater (Minnig et al, 2018) [8] and solid waste disposal (Wakida and Lerner 2005) [9]. In Europe, policies to reduce NH4+ and NO3− losses have been in place since nearly 30 years following the issue of the Nitrates Directive (ND; EC 1991) [14]. Wild et al, (2018) [15] argue that it will take several decades to significantly reduce nitrate concentrations in porous aquifers via denitrification, even if future nitrate inputs were considerably reduced
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