Self-purification monitoring of the Danube delta and Merlo river aquatic water according to microbiological indicators

Abstract

Purpose. Analysis of self-purification monitoring of the water area of the Danube delta and the small Merlo river (tributary of the Vorskla) according to microbiological indicators. Methods. To evaluate the role of microorganisms in maintaining the homeostasis of aquatic ecosystems, to study the intensity of self-cleaning processes and bioindication of pollution, the qualitative and quantitative characteristics of various ecological and trophic groups were determined. The dynamics and intensity of self-cleaning processes were determined by the ratio indicator (Ri) of TBC of autochthonous and allochthonous saprophytic microorganisms. The level of trophicity and saprobity in the Merlo river was determined by phenomenological signs. Results. It was established that the most intensive processes of self-purification were observed in the water area of the Danube delta above Reni city and in the Bystry branch. The most polluted water areas among studied were in the Kiliya branch near the town of Izmail, below the town of Kiliya and above the town of Vylkove (9th km). Monitoring studies of the Merlo river, in the area of the wastewater discharge in it of the food industry enterprise, were carried out according to hydrobiological and microbiological indicators. It was established that the river is very polluted, is under a large anthropogenic load on the water ecosystem and has a low ratio indicator (Ri). It was determined that according to the degree of saprobity and trophicity, the river in the wastewater discharge zone is related to hypertrophic and polysaprobic. After reconstruction of the treatment facilities at the food industry enterprise, the situation at the wastewater discharge point changed: Ri has increased from 1.1 to 3.2, and the water area at the discharge point has been classified as a polysaprobic zone, with signs of a mesosaprobic zone, which indicates a tendency to self-purification. Conclusions. It was established that the degree of self-cleaning processes is affected by anthropogenic sources of pollution of water bodies. The water ecosystems of the Danube delta have more pronounced tendencies to self-recovery than the ecosystems of the small Merlo river (a tributary of the Vorskla river). The positive impact of effective treatment of industrial wastewater discharged into the river on Ri, as well as on the trophicity and saprobity of ecosystems, has been established.