Between 6th August and 2nd September, 2021, a total of 66 lakes in Central and Eastern Yakutia were assessed as part of the joint Russian-German expedition (NEFU-AWI; RU-Land_2021_Yakutia). Samples and data were obtained with a large variety of different methods and for a wide range of sampling purposes. This dataset presents the results of hydrochemical laboratory analyses of ion concentration. Of those 66 hydrochemical analyses, 15 are from mountain lakes located within the Verkhoyansk mountain range, at the eastern end of the expedition route, including mostly intermontane basin or glacial lakes (average elevation: c. 1080 m a.s.l.). 13 lakes were sampled in Oymyakonsky District and two lakes in Tomponsky District. The hydrochemical dataset from the other 52 lakes that lie within the eastern extent of the Central Yakutian Lowland (average elevation: c. 190 m a.s.l.) represents thermokarst lakes. Thermokarst lakes originate from thawing of ice-rich permafrost and were found in different stages of their development, with a wide range of anthropogenic impact. These 52 thermokarst lakes include seven lakes within the Churapchinsky District, two are located in the Tattinsky District further east within a freshly burned forest. 42 lakes are located in Megino-Kangalassky District, of which 17 lakes are around Tungulu, and 24 lakes around Maya settlements.

Method: Surface water of lakes was obtained from ca 50 cm water depth. Fieldwork treatment of the water samples for anions and cations included a filtering step through 0.45 µm pore-size pre-syringe cellulose-acetate filters into 8 ml wide mouth bottles (anions), and 15 ml falcon tubes (cations), with a conservation step for cations by adding 65% HNO3. The ionic composition of surface water was measured at the dedicated hydrochemical laboratory of Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Potsdam, Germany.