Home – Home – Jornals – Contemporary Problems of Ecology 2021 number 4

History of large oil (petroleum) spills in freshwaters is delineated, processes of physical-chemical and biological degradation of oil are regarded. Toxicity of oil for hydrobionts and effects of oil pollution on communities of plankton, benthos and ichthyofauna, as well as problems of removal of ecological consequences of oil spills are discussed. State of ecosystem of Lake Pyasino before the catastrophic spill of 2020, namely hydrochemical indicators, species composition, abundance and biomass of plankton, benthos and fish are described. Possible ways of recovery of ecosystem of Lake Pyasino are suggested, including a biomanipulation “bottom-up”.

The results of the hydrochemical analysis of consequences of the accidental fuel release in the Norilsk-Pyasino water system are presented. Pollution of watercourses in the catchment of lake Pyasino (сreek nameless/Nadezhdinsky, R. Daldykan, R. Ambarnaya) by oil products, phenols, easily oxidizable and hard to oxidize organic matter (COD, PO and BOD ₅), suspended solids, inorganic salts and heavy metals with excess in MPS (including for fishery) as well as a temperature rise in waters of nameless сreek nearby Norilsk Heat & Power Plant 3 were revealed. Contamination of the surface water decreases downstream in ascending order: nameless сreek - Daldykan River - Ambarnaya River. The occurrence of petrochemical products, phenols and organic substances in the surface waters in two months after that spill is obviously due to their diffusion from the river bottom sediments, which accumulated a considerable amount of heavy fractions of diesel fuel after the accident. Increased concentrations of Ca, Cu, Zn, Mn, Co and Ni in waters of investigated tributaries of Lake Pyasino are not directly related to the accident; it results from the general technogeneous pollution of the territory and the increased geochemical background for the elements considered. Water contamination by oil products and phenols in the studied sections of Lake Pyasino (its central and northern parts) and R. Pyasino was not detected. However, concentrations of Pb exceeded MAP and Cd was present in the water, probably, due to accumulated pollutants in previous years.

In this work, analysis of bottom sediments (BS) samples and columns was conducted for the total content of petroleum products (hydrocarbons) of the Norilo-Pyasinsk group water reservoir, which were contaminated as a result of JSC NTEK CHPP-3 reservoir diesel spill nearby Norilsk. Processing two analysis methods used: fluorometric and gas chromatographic, meanwhile in addition the n-alkanes distributions of obtained BS extracts with gas chromatography were studied, the contribution of the total hydrocarbon content in diesel fuel so as hydrocarbons of slightly mature organic matter in contemporary sediments. Determination hydrocarbon composition of BS diesel fuel and chloroform extracts was processed. As a result, the levels of BS pollution by hydrocarbons for Pyasino Lake appeared insignificant with their background content comparison, and the maximum pollution revealed for the Ambarnaya River BS.

For the first time, the bacterial composition of water and sediments in Lake Pyasino and adjacent rivers was studied by next-generation sequencing. On the river sections exposed to diesel spillage in May 2020, no hydrocarbon-degrading bacteria were found. The Daldykan and Ambarnaya rivers, located downstream of the spill site, were dominated by bacteria that oxidize sulfur and heavy metals. At the same time, these bacteria were not found in Lake Pyasino which was dominated by small cyanobacteria. Thus, the composition of bacteria in the water and sediments of the Norilsk-Pyasino lake-river system corresponds to the technogenic impact to which it is exposed, and also demonstrates the buffer properties of Lake Pyasino on the way of water flow into the Kara Sea.

The assessment of species composition, abundance, biomass, and pigment characteristics of phytoperiphyton and phytoplankton of Lake Pyasino, its tributaries (Bezymyannyi stream, the Daldykan, Ambarnaya, and Norilskaya rivers), and the head of the Pyasina river was carried out after man-made accident - diesel fuel spill in vicinity of the city of Norilsk in May 2020. Significant decline of biomass and changes in species composition of phytoperiphyton after water contamination by fuel was revealed near the spillage site only (in the Daldykan river and in the Ambarnaya river downstream the Daldykan mouth). Downstream, in the Ambarnaya mouth zone, as a response to the release of a large amount of nutrients during the decomposition of oil products and dead organisms, as well as mechanical cleaning of the bank line, in the water column there was a massive growth of diatom and green algae ( Tabularia tabulata , Spirogyra sp.) and indicators of organic pollution (Euglenophyceae and Cryptophyceae) appeared. Significant changes in the plankton of Lake Pyasino and river Pyasina in comparison with the data obtained in the second half of the XX century (i. e., long before the accident) were not found. Species composition and quantitative features as well as amount and ratio of pigments characterized phytoplankton and phytoperiphyton of Lake Pyasino and the Pyasina river as normally functioning freshwater community of oligotrophic waters. All this indicates the absence of a negative impact of the accidental oil spillage on the ecosystem of Lake Pyasino and the Pyasina river.

The large Norilsk expedition of the SB RAS at the beginning of August, 2 months after the spill of 20 thousand tons of diesel fuel into the Bezymyanny stream, which took it out to the Daldykan and Ambarnaya rivers, took samples of net zooplankton at 13 stations, located in both sections of these rivers and Lake Pyasino with the outflow of the Pyasina River. Comparative analysis of the species composition, abundance, biomass and saprobity index of zooplankton at these stations has been carried out. The productions of rotifer and crustacean zooplankton and potential production of planktivorous fish in Lake Pyasino have been calculated. Based on the state of zooplankton, a gradual improvement in water quality has been observed from river areas exposed to the oil products to the northern part of the lake and the River Pyasina outflow. The low abundance and biomass of zooplankton in the lake (43800 ± 17550 ind./m³, 112.8 ± 26.2 mg/m³, on average) due to the dominance of rotifers ( Ploesoma truncatum (Levander), Bipalpus hudsoni (Imhof), Conochilus unicornis Rousselet) resulted in low values of zooplankton production and potential production of planktivorous fish (0.85 kg/ha per season).

The species composition and quantitative characteristics of the zoobenthos of Lake Pyasino and rivers flowing into it after the diesel spill have been analyzed. The production of zoobenthos and potential production of benthivorous fish in Lake Pyasino have been calculated. A small number of zoobenthos species, low values of abundance and biomass were revealed. In the Bezymyanny stream, the mouth of the Daldykan and Ambarnaya rivers, oligochaetes Limnodrilus hoffmeisteri Claparede and Tubifex tubifex (O. F. Muller) dominated in zoobenthos abundance and biomass. In Lake Pyasino and the Pyasina River outflow, larvae of caddis flies, chironomids, stoneflies, and amphipods prevailed. In the area of deep-water silted station of Lake Pyasino, oligochaetes L. hoffmeisteri developed, the proportion of which in the benthofauna at this station (40 and 79 % of the total biomass and abundance respectively) was maximal. Amphipod Monoporeia affinis (Lindstrцm) dominated in biomass at this station. A decrease in chironomid diversity, an increase in the proportion of polysaprobic oligochaetes, and lower values of the Shannon index in Lake Pyasino in 2020 compared to 1992 were noted. The low abundance (2181 ± 2048 ind./m²) and biomass (2.01 ± 1.85 g/m²) of zoobenthos in the lake resulted in low values of zoobenthos production and potential production of benthivores fish (3 kg/ha per season). Based on the state of zoobenthos, improvement of water quality has been observed from river sections exposed to the oil spill to the lake and the outflow of the River Pyasina.