State of the Environment
Bulgaria 2003
SURFACE WATER STATUS IN BULGARIA
The indicators presented below indicate the changes in the concentration levels for selected surface water parameters. Six parameters which describe the chemical status of the surface water are chosen from the available data set in the Bulgarian Monitoring network to describe changes in the state of environment;: dissolved oxygen, BOD 5, COD – Mn, ammonium and nitrate nitrogen and phosphates. The information covers only rivers and streams for the period between 1990 -2001. Clear decreasing trend is observed in most parameters and especially in the BOD and COD concentrations. Only the parameters dissolved oxygen and phosphates have been relatively stable during the observed period. The results are shown in the following figure.
More statistical information for individual parameters is shown in the next boxplots figures. A boxplot characterizes the distribution and dispersion of a variable, displaying its median and quartiles. Special symbols identify the position of outliers and extreme values. The number of yearly analyzed samplings and value for 90 percentiles are also included. All presented parameters show slight tendency to increase in the year 2001. The reasons for this trend are the privatization process and the socio-economic changes.
The next figure presents the water quality classification according to the nationa Regulation on water quality assessment. There are three classes identified and the figure illustrates general improvement in the river water quality in terms of chemical properties of the rivers. The assessment has been made on the basis of nine important parameters as follows: dissolved oxygen, conductivity, BOD5, COD – Mn, suspended solids, ammonium nitrogen, nitrite nitrogen, nitrate nitrogen and phosphates.
Last update on March 2003