We investigated chironomid fauna of surface sediments and a short sediment core (Bol’shoy Kharbey Lake) from Pechora river basin, Northern Russia. Twenty three investigated lakes have thermokarst, glacial or floodplain origin and are characterised by low mineralization, mostly hydrocarbon-calcium type of water and low concentration of nutrients. Most of the lakes have circumneutral pH around ≤7 and only two lakes are slightly more acidic with pH ≤ 6. Ninety six chironomid taxa were identified in the surface sediments. Distribution of chironomids in the studied region is driven by continentality, mean T_July and рН. Chironomid communities from the core of the B. Kharbei Lake demonstrate the highest similarity with the fauna of the deeper lakes of the glacial origin. The glacial lakes have the highest indices of continentality and the lowest winter temperatures within the investigated data set. The chironomid fauna of the glacial lakes is composed of the profundal, oligotrophic and cold-stenotherm taxa. The fauna of the floodplain and thermokarst lakes is more closely related to T_July and is composed of littoral and phytophilic taxa of meso–or eutrophic waters and moderate temperature conditions. The fauna of the acidic thermokarst lakes considerably differs from the other lakes. Chironomid communities here are represented by tolerant to acidification taxa, and by the typically littoral and shallow water acid-tolerant taxa that apparently also can tolerate acidification. Studied sediment record covers ca last 200 years. The reconstructed T_July during the entire period remain slightly below the modern temperatures. From 1970 reconstructed T_July shows steady increase to the modern level. The reconstructed water depths (WDs) of the lake are higher than today till 1980. The highest WDs are reconstructed for ca 1970. After that the WDs gradually decrease to the modern level. Changes of the WDs are most probably related to changes in the precipitation rate.

This paper presents the first study of five small lakes located in the city of Murmansk. Field work was carried out during 2018–2019. Water samples were collected using a bathometer, while the sediments were sampled using an Ekman grab and Limnos gravity corer. It was found that the water of the studied lakes in Murmansk belong to the sodium group of the chloride class and to the calcium group of the hydrocarbonate class. Compared to the background level, elevated pH, concentrations of the main cations of alkali and alkaline-earth metals, N compounds, total dissolved solids, and heavy metals were found in the lakes, which indicate exposure to anthropogenic impacts. The sediments of the lakes, composed of organomineral and mineral silts, also have an elevated content of heavy metals compared to the background. The most significant excessive concentrations were found for V, Ni, Sb, Pb, Co, Cr, and W. Based on the calculated pollution load index and geoaccumulation index of the sediments, the studied water bodies in Murmansk can be classified as lakes with heavy and extremely heavy pollution levels. The primary pollution sources are emissions from the Murmansk thermal power plant, coal port, road and, rail transport.