Problems of quality assessment of highly colored water of Lake Onego urbanized tributary using hydrochemical, microbiological and toxicological indicators

Abstract

The article presents the results for 2014–2015 of chemical, microbiological and toxicological studies of the water quality of the urbanized tributary of Lake Onego (the River Neglinka). The high anthropogenic load on the studied river was revealed. The runoff of storm water reached one third of the river runoff. The maximum excess of maximum available concentration in storm water for BOD₅ was 80–90-fold, for oil products – 50–60-fold, for suspended solids – 40-fold. The River Neglinka in the upper reaches (outside the urban area) is affected by a swampy catchment area. The chemical composition of the water (low pH values, high color index, COD_Cr and Fe_tot) reflected the influence of catchment area. The methodological problems were associated with identifying zones of anthropogenic impact against the background of the negative impact of natural factors on the water quality of the River Neglinka. In the calculation a modified specific combined water contamination index was used. This made it possible to determine zones of influence of the anthropogenic factor. Microbiological indicators (total bacterial abundant, total coliform bacteria, saprophytic bacteria) indicated a high degree of pollution of the River Neglinka and especially sanitary-indicative bacteria. The unsuitability of the River Neglinka for recreational use was revealed. Bioassay revealed the toxicity of the river water in the upper reaches. It was connected with the low pH due runoff of humic substances from swampy catchment area. The barrier role of groundwater, which led to an increase in the pH, and the complexing ability of humic substances, which reduced the bioavailability of heavy metals, stipulated non toxicity river water in urban areas. The study proved that the assessment of the quality of highly colored river waters is possible only with a comprehensive implementation of chemical, microbiological and toxicological studies.