Relationship between the concentrations of nitrogen compounds and the water discharge in the Chirchiq River, Uzbekistan

Abstract

Abstract The Chirchiq River is one of the most human affected important drinking and municipal water source in the Republic of Uzbekistan. This work aimed to study the level of water pollution in the Chirchiq River by nitrogen compounds (ammonium, nitrite, and nitrate) over the last decade (2008-2018) with the identification of possible correlations between the level of water pollution and discharge. Most common pollutants: ammonium, nitrite, and nitrate concentrations in water were determined using generally accepted photometric methods. Correlation analysis of relationships between the river discharge and the concentrations of these compounds was carried out for each of 9 hydropost for each year and multiyear average values of the ten years (2008-2017). The water quality in the upstream part of the river is evaluated as a very good, however, in mid- and down streams due to diversion of nitrogen-containing organic and inorganic wastewater into the river worsening the water quality abruptly and concentrations exceeding MPC for fishery water bodies up to 5-8 times. Fortunately, according to the [NO3¯]: [NO2¯]: [NH4 +] ratio, the river has still enough assimilation capacity to transform hazardous ammonium and nitrite forms into nitrate nitrogen. Obtained results did not confirm the existence of significant interdependencies between the nitrogen compounds and water discharge. The results of the study will provide a theoretical and practical basis in terms of elucidating the mechanism of hydrochemical transformation of nitrogenous compounds along with the river ecosystem and predicting the dynamics of their concentrations in river water.