Figure 1
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Data sources:
Data was provided by National Environmental Agency of the Ministry of Environmental Protection and Agriculture under the ENI SEIS II East project activities
Note: The data series are calculated as the average of annual mean of BOD5 (mg O2/l) (top), and ammonium concentration (mg NH4-N/l) (bottom) for river sites in the two major river basins of Georgia (Black Sea and Caspian Sea basins) and for the whole country for the period 2004-2018. The total number of river sites is given in parenthesis.
Biochemical oxygen demand (BOD) and ammonium are key indicators of organic pollution in water. BOD shows how much dissolved oxygen is needed for the decomposition of organic matter present in water. Concentrations of these parameters normally increase as a result of organic pollution caused by discharges from waste-water treatment plants, industrial effluents and agricultural run-off. Severe organic pollution may lead to rapid de-oxygenation of river water, high concentration of ammonia and disappearance of fish and aquatic invertebrates. Some of the year-to-year variation can be explained by variation in precipitation and runoff.
Average BOD has decreased somewhat over the time period 2004-2018. Comparing the average of the last three years to that of the first three years, average BOD has decreased by 11% for the country as a whole. The main decrease is seen for the Black Sea basin (21%). The average for the Caspian Sea basin increased towards 2006 but has decreased since then.
Average ammonium concentration showed a more pronounced decrease (50% for the whole country). The largest decrease was observed for rivers draining to the Caspian Sea (62%).
The middle of the time series should be treated with some caution, due to lower number of samples per year. This goes in particular for the years 2011-13 and the Caspian Sea basin. This may explain some of the variability observed for ammonium concentration in this period.
The decrease in BOD and ammonium concentrations can be attributed to measures taken, e.g. improvement of the urban and industrial wastewater treatment. Further improvement is expected in particular for the Black Sea river basin where the large cities have not had waste-water treatment plants. Treatment plants are currently under construction in Zugdidi and Poti and construction of a treatment plant in Kutaisi is planned.