Scientific publications

This work focuses on the evaluation of the ecological status of the Izhora River using composite indices. The river’s hydrochemical and hydrobiological (bioindication and bioassay) characteristics were analyzed. The composite index was calculated using the method of summary indicators. Initially, the water quality was estimated on the basis of single hydrochemical and hydrobiological characteristics. The source area of the river is characterized as “clean” by the values of the water pollution index and the biotic index. However, there was a predominance of oligochaetes in the bottom communities. The upper- and middle reaches of the Izhora River are in a more favourable condition judging by hydrochemical and hydrobiological characteristics. The lowest recorded values of saprobity were in the 2.56–2.86 range. According to the oligochaete index, the water is classified as “clean”. The Woodiwiss index places the water into the “clean” – “moderately polluted” range. Water in the river mouth has the highest values for the saprobity index (3.50) and the oligochaete index (98 %). According to the Woodiwiss index, the water is classified as “dirty”. Such results are well correlated with the evaluation of water quality by hydrochemical indicators. There are high levels of organic substances (4x maximum permissible concentrations) and low oxygen content, high water pollution index (“moderately polluted” quality class). Next, a classification model was proposed for obtaining an integral value of the ecological status of the watercourse. Its priority parameters are: water pollution index; Pantle – Buck saprobity index modified by Chertoprud; Goodnight – Whitley Index (modified by Parele); Woodiwiss Biotic Index (Trent Biotic Index), and results of natural water bioassay using Chlorella vulgaris Beijer and Paramecium caudatum Ehrenberg. The index was calculated for five categories of the ecological status. Calculations of the composite index revealed that a good ecological status is characteristic of channels in the middle course. The source area of the river is in satisfactory ecological condition according to the value of the integral index. As the river originates from a spring, the area is characterized by low oxygen content and, consequently, a predominance of organisms resistant to its deficiency. The ecological status of the mouth section of the river is poor. This is evidenced not only by the exceedance of regulatory limits for the main pollutants and toxic effects, but also by the presence of indicator species of saprobic pollution and very low species richness of macrozoobenthos.