Modeling Nitrogen behavior in Tigris River Using System Dynamics Approach

Abstract

Nitrogen behavior across multimedia environment like Tigris River is complex process resulting in a number of interactions of the biogeochemical processes. A solid understanding of the interacted processes is critical to evaluate river system performance. Inorganic nitrogen including ammonium ion (NH4+), free ammonia (NH3), total ammoniacal nitrogen (NHx), nitrite (NO2-), nitrate (NO3-), total oxidized nitrogen (NOx), and total inorganic nitrogen (TIN) in Tigris River were examined from April 2018 to March 2020. A simple system model was implemented to simulate and to help interpret the trend of inorganic N forms based on datasets collected from the river system. It is indicated that the obtained results revealed that the dynamic model was able to represent and predict NHx and NOx behavior in Tigris River. Root mean squared errors between actual and predicted concentrations for NHx and NOx were 0.053 and 0.312 g m-3, respectively. Modeling analysis confirmed the steady-state dynamics of NHx and NOx over the course of the study. Average concentration for NHx was 0.37±0.05 g m-3, while mean value of NOx levels was 2.18±0.33 g m-3 in the Tigris river water. The results from this study also supported by the changes of the water budget, chemical oxygen demand, pH, dissolved oxygen, electrical conductivity, and water temperature in the river system. The results suggest that the microbial mechanisms are the principal N transformation processes in the river system. Findings presented in this research could help to improve conceptual understanding of N behavior in Tigris River, and therefore could assist decision makers to select best management practices and to develop mitigation strategies to sustain water quality in Tigris River.