CHANGES IN CONCENTRATIONS OF ORGANIC MATTER IN THE MOUTHS OF THE DOTNUVELE AND SMILGA RIVERS

Abstract

The quality of water in rivers of central Lithuania is often bad due to intensive anthropogenic activities. When rivers flow through the town’s territory, concentrated pollution, such as rainwater, industrial and productional waste water discharges, contributes to diffuse sources of pollution. If biogenic substances are the main indicators for diffuse pollution, organic matter, expressed as BOD, is the indicator for concentrated pollution. The article provides the 2013 – 2017 monitoring data on the changes of organic matter in the water of the Dotnuvele and Smilga Rivers and discusses the reasons for fluctuations in concentrations of BOD₇. The aim of the research is to investigate the changes in the organic matter of the Dotnuvele and Smilga Rivers, depending on meteorological factors.
For chemical analysis, water samples were taken quarterly. Water analysis was carried out by the ASU Chemical Analytical Laboratory of Water Resources Engineering Institute. The amount of organic matter (BOD₇) is calculated as the difference in oxygen content after 7 days of incubation, while the amount of dissolved oxygen (O₂) in the water is determined by the electrochemical probe method. The concentrations of BOD₇ and O₂ in the water of both rivers is compared with the criteria for assessing the ecological status of surface water bodies.
The research has shown that the dissolved oxygen concentrations in rivers’ water are strongly influenced by water temperature and precipitation. The lower the temperature, the more of the dissolved oxygen is found in rivers’ water (r = -0.64). A lower precipitation amount, which reaches the rivers, increases the amount of dissolved oxygen in them (r = -0.45). The increase of BOD₇ concentrations in rivers’ water was caused by higher precipitation amount (r = 0.46), higher air (r = 0.41) and lower water temperature (r = -0.41). The ecological status of the Dotnuvele River was usually good, while Smilga was average.

Keywords: biochemical oxygen demand, dissolved oxygen, concentration, ecological state, surface water

Article DOI: http://doi.org/10.15544/RD.2017.095