Dubysos upės vandens kokybės vertinimas Raseinių rajone ; Evaluation of Dubysa water quality in Raseiniai region

The aim of study – to evaluate water quality of Dubysa river in Raseiniai region. The paper analyzes the dissolved oxygen, biochemical oxygen demand (BOD7) and ammonium nitrogen, mineral nitrogen, total nitrogen, nitrites, nitrates, phosphates and total phosphorus concentration dynamics in 1997–2009 and Raseiniai waste water treatment efficiency in 2000–2009. It was found, that according to biochemical oxygen demand water is very clean (I quality class). Study of water quality according to the nitrogen concentration showed, that near the Kaulakiai water is slightly (III quality class), but near Ariogala – an average of polluted (IV quality class). According to phosphates concentration Dubysa is clean river (II quality class). At research areas of multi-annual average BOD7, ammonium nitrogen, nitrite, total phosphorus and phosphate levels did not exceed the MRL in 1997–2009. This mean that Raseiniai region is not industrial, and that the river flow is relatively fast – spills into the water they are rapidly diluted. The assessment of water quality according to generally nitrate concentrations in surface waters found in the hydrochemical characteristic quantity (0,003 mg/l), we can say that the river water is severely polluted by nitrogen compounds. Concentration of the dissolved oxygen in water has exceeded of 6 mg/l – hydrochemical indicator of the fishery has exceeded the rate applicable to MKL in all study years. Raseiniai waste water treatment enterprise is working quite effectively: by total nitrogen removal efficiencies – 79,6 %, according to BDS7 rate – 93,4 %, according to material in suspension – 92 %.