Phytoremediation of oil pollution using free-floating aquatic plants is a promising method for water body cleaning. In this study, the influence of Eichhornia crassipes and Pistia stratiotes on the degradation of oil pollution was investigated. The loss of oil alkanes and the rheological characteristics of water were evaluated, and an analysis of the emerging rhizospheric microbial communities was carried out using high-throughput sequencing. The presence of E. crassipes and P. stratiotes plants in oil-contaminated tanks had no effect on the degradation of oil alkanes. However, the presence of plants promoted the development of rhizospheric bacteria capable of growing in oil-contaminated environments. Alpha diversity of microbial communities in oil-contaminated samples was higher in the presence of plants. Additionally, plants significantly reduced the water/oil interfacial tension, which facilitated the availability of hydrocarbons for biodegradation. A difference was noted in the microbiome between E. crassipes and P. stratiotes. Changes in the composition of microbial communities highlight the potential of E. crassipes and P. stratiotes as rhizospheric hosts for microorganisms in the phytoremediation of water bodies.

Depending on the season, the primary production of planktonic communities determined by radiotracer analysis varied within a broad range, from 6 to 314 µg C/(L h). Primary production in cyanobacterial mats was 4.2‒10.9 × 10³ µg C/(dm³ h), and Chl a content varied from 6‒13 to 132‒140 mg Chl a/m². For the plankton, the highest values were revealed in summer (25‒46 mg Chl a/m³), with the maximum in August (223 mg Chl a/m³). High abundance of bacterioplankton (0.3‒7.4 × 10⁶ cells/mL) and massive growth of diatoms (0.15 × 10⁶ cells/mL) with predominance of the genus Chaetoceros were found. Sulfate reduction rates varied from 0.037 µmol S/(dm³ h) in the upper reach to 61.87 µmol S/(dm³ h) in the river mouth.

Anammox bacteria are promising for treatment of wastewater with high ammonium content. Immobilization of microbial communities on various carriers for biocenosis attachment is a widespread technological approach, increasing the productivity and reliability of wastewater treatment biotechnologies. Compared to the Polyvom stationary biomass carrier and Etek and Mutag moving-bed carriers, the new type of stationary biomass carrier based on a nonwoven material resulted in the best specific productivity values, both per volume and per carrier area. The new stationary carrier is promising for application at wastewater treatment plants.

Primary production of phototrophic communities was determined in the shallow Chernavka River, which flows into the self-settling Lake Elton: planktonic—from 0.025 to 0.256 mg C/(L h), benthic—from 9.6 to 12.5 mg C/(dm³ h), algal (Ulva-thread algae) and cyanobacterial mats—from 4.6 to 8.76 mg C/(dm³ h). The rate of dark CO₂ assimilationvaried from 14 to 31.8 mg C/(L day) in the water and from 2.6 to 69 mg C/(dm³ day) in the sediments, indicating a high variability of heterotrophic processes. High concentrations of organic compounds in surface waters were found; for lipids, aliphatic hydrocarbons, and polycyclic aromatic hydrocarbons they averaged 692, 80 and 0.79 μg/L, respectively. The composition of aliphatic hydrocarbons in the sediments was characterized by planktonogenic low molecular weight homologues n-C₁₅–C₁₇ and a sharp increase in the series of odd high molecular weight alkanes, whereas the composition of polycyclic aromatic hydrocarbons was characterized by an increased proportion of naphthalene. Predominant sequences in the 16S rRNA gene library obtained for the sediments belonged to Pseudomonadota (69.09%), Bacteroidota (11.64%) and Chloroflexota (7.92%) phyla.

Depending on the season, the primary production of planktonic communities determined by radiotracer analysis varied within a broad range, from 6 to 314 µg C/(L h). Primary production in cyanobacterial mats was 4.2‒10.9 × 103 µg C/(dm3 h), and Chl a content varied from 6‒13 to 132‒140 mg Chl a/m2. For the plankton, the highest values were revealed in summer (25‒46 mg Chl a/m3), with the maximum in August (223 mg Chl a/m3. High abundance of bacterioplankton (0.3‒7.4 × 106 cells/mL) and massive growth of diatoms (0.15 × 106 cells/mL) with predominance of the genus Chaetoceros were found. Sulfate reduction rates varied from 0.037 µmol S/(dm3 h) in the upper reach to 61.87 µmol S/(dm3 h) in the river mouth.