Spatial and Temporal Analysis of Nitrate Dynamics along the Tigris River

Given the wide dependency on surface water used to supply drinking water, agricultural irrigation, and industrial activities, nitrate pollution has posed a serious concern in the Tigris River in recent years. The main objective of this study was to develop an understanding of the spatiotemporal patterns of nitrate distribution in the Tigris River through an integrated approach using hydrological data, physicochemical parameters, and model-based analysis. Eighty-four monthly sampling campaigns from forty monitoring locations along the Tigris River were carried out from January 2011 to December 2018. Obtained results demonstrated that the NO3- dynamics were strongly correlated with the length of transport distance and flow rates along the river system (p < 0.05). High flow rates in the upper courses of the river system favored physical transport of NO3- and promoted a dilution effect. However, low flow rates in the lower sections favored the accumulation processes of NO3- and promoted a concentration effect. High concentration of 7.0±1.96 g NO3- m-3 was observed in February 2018 downstream in the river. No significant seasonal effect in NO3- concentrations were observed. These results were supported by the changes in dissolved oxygen concentration and pH in the river system and indicated high nitrification rates and elevated NO3- accumulation, particularly downstream in the river. This modeling approach has also confirmed field observations of NO3- dynamics with 65% of the variances in the river system being explained by the model.