Significance: Russian rivers are the predominant source of riverine mercury to the Arctic Ocean, where methylmercury biomagnifies to high levels in food webs. Pollution controls are thought to have decreased late–20th-century mercury loading to Arctic watersheds, but there are no published long-term observations on mercury in Russian rivers. Here, we present a unique hydrochemistry dataset to determine trends in Russian river particulate mercury concentrations and fluxes in recent decades. Using hydrologic and mercury deposition modeling together with multivariate time series analysis, we determine that 70 to 90% declines in particulate mercury fluxes were driven by pollution reductions and sedimentation in reservoirs. Results suggest that Russian rivers likely dominated over all other sources of mercury to the Arctic Ocean until recently.

The objective of this study was to evaluate subaerial taliks’ geology, configuration, ground temperature and groundwater level in the continuous permafrost environment of Central Yakutia (Eastern Siberia). The study included geophysical surveys, borehole drilling and measurements of ground temperature and groundwater level variation in a talik aquifer in the Shestakovka research watershed. The talik occupies a gentle, sandy slope covered by a sparse pine forest. Its thickness varies from 3 to 17 m. The talik has several water-conducting branches along its slope. The seasonal thaw layer outside the talik and the talik itself form a single aquifer at the end of the summer. Water-saturated deposits in the talik have a temperature of about 0 °C throughout the year and do not freeze because of the constant filtration of water through the pores and convective heat transfer. Although the groundwater level is relatively close to the land surface, at a depth of just 1–3 m, it has very weak response to snowmelt and precipitation events. The maximum groundwater level occurs in February under cryogenic pressure due to deep seasonal ground freezing above the talik aquifer. Complicated relations between the landscape and the groundwater in the given geological conditions lead to the long-term existence of talik aquifers in the continuous permafrost environment.

The results of long-term studies of a group of aufeis-forming Buluus groundwater sources are given. A stow, which has been formed by the spring, contains the drainage area of the suprapermafrost–intrapermafrost aquifer, which is widespread in the sand deposits of the bestyakhskaya terrace of the Lena River in Central Yakutia. The analysis of observations of 1964–2017 showed stable water chemistry in Buluus spring at the long-term scale. Considerable seasonal variations of water chemistry are typical of low-discharge springs, which start functioning after becoming free of aufeis. The spring water also shows higher concentrations of lithium and fluorine. The possible causes of the different chemistry of spring water are discussed, with special attention paid to the local activity of rock freezing and thawing processes in the aufeis valley. It is shown that groundwater samples are to be taken from all springs in the areas of their group discharge with the aim to assess the effect of natural and technogenic factors on the permafrost–hydrogeochemical conditions.

A study was performed to evaluate the current permafrost and groundwater conditions in the reclaimed floodplain of the Lena, one of the largest rivers in the permafrost zone. Data from ongoing hydrogeological monitoring were compared with earlier observations conducted during the reclamation process. The results demonstrate that the placement of dredged fill led to the development of suprapermafrost thaw zones (taliks). The anthropogenic taliks vary in thickness from 10 to 15 m in areas of buried bars to 20 m or more in the former locations of oxbow lakes. There is similarity in seasonal groundwater fluctuation patterns and response to river stage variations across the study area suggesting that a continuous aquifer connected to surface water. The connection with the river is most evident during the spring flood period. Two mechanisms of ground saturation are identified during this time. One is lateral seepage flow from the Lena River into the fill mass. The zone of its influence is limited to 150–170 m from the stream. The second is hydraulic pressure transmission from the river through the subchannel flow connected with the anthropogenic suprapermafrost aquifer. Its influence extends across the entire fill area. Continuous water movement at the base of the fill prevents permafrost aggradation from below. The study results should be taken into account when developing and implementing design and construction standards for engineering structures in the reclaimed floodplains of the permafrost zone.

Особенности рельефа и строения криолитозоны Центральной Якутии связаны с широким распространением здесь позднечетвертичных супесчаных дюнных покровов. Они вмещают разветвлённые сети обводнённых межмерзлотных таликов, гидравлически связанных эоловых озёр, подземных источников, фрагменты едомных отложений с мощными ледяными жилами, а также наледи. На основе выборки более чем из 430 определений обсуждается разнообразие состава стабильных изотопов (¹⁸O и D) перечисленных компонентов водного стока.