Monitoring Dissolved Oxygen in the Hrazdan River

Duration: 2007-2008

Acopian Center for the Environment
Washington University

image001The HrazdanRiver is the primary waterway in Armenia and country’s second largest river.  While the Hrazdan receives effluent from various agricultural, commercial, industrial, and residential sources, it is most significantly impacted by the discharge of Yerevan’s almost entirely untreated wastewater.  The effects of this poorly treated wastewater are evident through a variety of water quality indicators, most notably through drastic drops in dissolved oxygen (DO) levels downstream of the city.

The aim of this study was to quantify the effect Yerevan’s wastewater discharge have on health of the Hrazdan River by monitoring dissolved oxygen levels in an 18-km stretch that began two kilometers upstream of the wastewater outfalls.

Water quality sampling was conducted from March to August 2008.  DO levels consistently dropped to below 5% of the saturated dissolved oxygen level (the maximum oxygen content achievable at the given temperature and pressure) and to levels well below those permitting a healthy aquatic ecosystem.  DO levels achieved partial re-aeration within the first 10 kilometers after the wastewater outfall, but they depreciated again, likely due to continued biological oxygen demand from agricultural runoff.  The 16 kilometers downstream of the wastewater outfalls in the study area were not sufficient for the river to achieve full re-aeration.

image007image004

Additional water quality, hydrologic, biological, atmospheric, and observational data was also collected during the course of this study and may later be used to generate a predictive model of the DO content of the river under different scenarios.