Mapping potential high nitrogen leaching zones using TETIS hydrological model

Agricultural intensification over recent decades has led to a growing reliance on irrigation schemes and nitrogen-based fertilizers to sustain crop productivity (FAO, 2020; Lassaletta et al., 2021, 2014). However, these practices enhanced nitrogen leaching processes, increasing the risk of groundwater pollution that can persist for more than a decade (Bijay-Singh and Craswell, 2021; FAO and IWMI, 2018; Lassaletta et al., 2014; Martin et al., 2021; Sebilo et al., 2013). Identifying zones prone to nitrogen leaching is therefore essential for sustainable agricultural management and long-term groundwater protection.

This study aims to identify and map potential high nitrogen leaching zones in the agricultural area near Valencia, Spain, covering the lowlands of the Júcar River basin, before its discharge into the Mediterranean Sea. The approach combines hydrological simulation with spatial analysis of agricultural practices. The distributed TETIS hydrological model (Frances et al., 2007, 2021) with its nitrogen module (Puertes et al., 2020) was applied for the period 1966 to 2015, to simulate water balance components and nitrogen transport under different irrigation and fertilizer practices. We evaluated five distinct management scenarios based on Pool et al (2022), comparing flood versus drip irrigation with nitrogen application rates ranging from 133 to 182 kg N ha⁻¹ year⁻¹. All simulations employed a calibrated set of 12 water balance parameters (Pool et al., 2021b, 2021a), together with the nitrogen cycle parameters estimated by Puertes et al (2021).

Based on the outputs, monthly, annual, and maximum daily recharge and leaching amounts were derived for each irrigation–fertilizer practice and parameterization. These values were analysed individually and in combination to delineate potential nitrogen leaching zones across the study area. The resulting spatial patterns provide valuable information that can support the Acequia Real del Júcar irrigation authority in identifying strategic locations for monitoring and controlling nitrogen leaching within the irrigated system.