Modelling Nitrate Output from Agricultural Watersheds Using a Hydrological Model

Abstract

Abstract A distributed area model called CEQNIT (CEQUEAU-NITRATE) to predict nitrate concentration and load from agricultural watersheds has been developed. The model application requires that the watershed be divided into partial squares. At partial-square scale, the model simulates nitrogen reactions within the soil and nitrate leaching. Nitrogen budget in the CEQNIT model includes the leaching of nitrate, plant uptake, denitrification, mineralization of organic nitrogen, immobilisation, nitrification, input by fertilizer and precipitation. Nitrogen dynamics were simulated as first-order kinetic reactions, and the influence of soil temperature and moisture were included. The model requires input from the CEQUEAU hydrological model that provides temporal and spatial estimation of flow discharge over the watershed. Using two-year data from a small agricultural watershed (78 ha), the model was calibrated with first-year data and tested with the second-year data. Results obtained from this study showed that the model was able to reproduce the seasonal nitrate fluctuations accurately.