Figure 2
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Data sources
- Data were provided by the Environment Quality Monitoring Division of the State Hydrometeorological Service of the Ministry of Agriculture, Regional Development and Environment, under the ENI SEIS II East project activities.
- Water quality database of Dniester river basin, State Hydrometeorological Service.
Note: The data series are calculated as the averages of annual means of nitrate concentrations (mg NO3-N/l) (top) and total phosphorus (mg P/l) (bottom) for three lakes in Moldova for the period 1992-2017.
The average nitrate concentration in rivers in the period 1992-2017 was 5.11 mg N/l. The highest peak in nitrate was in 1998 (11.70 mg N/l) and the lowest in 2010 (3.08 mg N/l). The overall trend in nitrate concentration in rivers is negative, but there are large difference between sub-periods. Between 1992 and 1998 the annual average concentrations of nitrate in freshwater were increasing, after which the trend changed. Between 1998 and 2005 the trend was significantly negative. In the 12 years from 2005 to 2017 there was no significant trend. Concentrations of nitrate fluctuate around a multiannual average of 4.3 mg N/l.
The highest concentrations of nitrates are found in the rivers in the Nistru basin (the average for the period 1992 -2017 was 7.38 mg N/l). Here, the maximum average annual concentration exceeded 15 mg N/l in 1998. Rivers in the Prut basins have an average annual concentration of 3.05 mg N/l; the highest concentrations were in 1994 (2.59 mg N/l) and 2001 (2.46 mg N/l).
The highest annual averages of total phosphorus concentration in rivers were in 2008, 2012 and 2016, when all values were above 0.34 mg P/l. There is no significant trend in phosphorus concentrations in the freshwaters of Moldova. In the Nistro basin, the phosphorus concentrations are slightly increasing. This may indicate a lack of waste water treatment and an increase in the use of phosphate-based detergents throughout the area.
The highest average nitrate concentration in lakes was in 1998, after which it started to steadily decrease. At present, the average annual nitrate concentration in lakes is lower than 0.5 mg N/l. The lowest concentration has been in Ghidighici lake on the river Bîc in the Chișinău area. All lakes showed negative trends in nitrate concentration following the peak in 1998. The reason for this might be a decrease in agricultural activities. The same negative nitrate trend has been seen in rivers as well.
The average total phosphorus concentration in the three lakes studied (Dubăsari Centrala Hidroelectrică, Costești Centrala Hidroelectrică and Ghidighici lake on the river Bîc (Vatra, Chișinău) was around 0.10 mg P/l between 1994 and 2007, after which the concentration started to increase. Nevertheless, this is due to a very high increase in phosphorus in Ghidighici lake in the Chișinău area. The other two lakes are reservoirs on rivers (used for hydroelectric power) and have rather stable and low phosphorus concentrations (< 0.1 mg P/l). The increasing trend in phosphorus in Ghidighici lake until 2012 might be related to a larger input of untreated urban waste water and greater use of phosphorus-based products in agriculture.