Model-based Analysis of Nitrogen Dynamics in the Tigris River in Baghdad City

Abstract

Developing a solid understanding of the nitrogen dynamics across the Tigris River is critical to evaluate the environmental degradation of the increased N fluxes. Nitrite, nitrate, and total oxidized N (nitrite+nitrate) were monitored from April 2018 to August 2019. Plug flow reactors and continuously stirred tank reactors in series models were implemented to explore N behavior in the river system. The results indicated that the total oxidized N decreased over the first half of the study period, then was followed by a high rate of nitrate production. These findings are also supported by changes of the river flow rates, dissolved oxygen, pH, and chemical oxygen demand. The models have the capacity to simulate N dynamics, with varied prediction errors. Root mean squared errors between measured and predicted nitrite, nitrate, and total oxidized N concentrations were 0.118, 2.595, and 2.560 g m-3, respectively, for the PFR model, while these values were 0.05, 0.175 g m-3, and 0.176 g m-3, respectively, for the CSTRS model. The correlation coefficients were 0.012, 0.925, and 0.922 for nitrite, nitrate, and total oxidized N, respectively, when the PFR model was applied. These values were 0.92, 0.99, and 0.99, respectively, after the application of the CSTRS model. Obtained results revealed that the modeling approach can provide a useful framework to improve understanding of N dynamics, which helps to develop mitigation strategies for sustaining water quality in the Tigris River.