Emerging solute-induced mineralization in Arctic rivers under climate warming

Permafrost degradation under a warming climate is accelerating the hydrological processes in Arctic river basins. However, corresponding changes in river mineralization, riverine solute exports and their potential influencing factors are not fully understood. In this study, we selected six major Arctic rivers (Ob, Yenisei, Lena, Kolyma, Yukon and Mackenzie Rivers) with different permafrost extents, meteorological conditions and hydrological regimes to reveal the changes in river mineralization and riverine solute exports using ArcticGRO sampling data from 2003 to 2019. Our results indicate that solute-induced river mineralization has already been observed in the Lena, Yukon and Mackenzie Rivers during 2003-2019. The annual flux of total dissolved solids (TDS; a key parameter of drinking water quality), calculated by the Load Estimator (LOADEST) program, from these six rivers was approximately 295.24 ± 12.50 Tg, with the Ob, Kolyma and Yukon Rivers exhibiting significant increasing trends (p < 0.05) at rates of 4.38 Tg/10 yr, 1.62 Tg/10 yr and 3.03 Tg/10 yr, respectively. Climate-induced changes in hydrological regimes regulate riverine solute exports, with relatively higher TDS concentrations in the groundwater-dominated winter low-flow season and lower TDS concentrations under the dilution of groundwater by snowmelt spring floods and summer precipitation events. The riverine solute fluxes with higher TDS concentrations (e.g., those of the Yukon and Mackenzie Rivers) increased more rapidly (~0.14 Tg/km³) with changes in river discharge; however, the TDS concentrations were more sensitive to climate warming in continuous permafrost-dominated colder basins (i.e., the Kolyma and Lena River basins) than in other relatively warmer basins. Our results suggest that riverine solute exports are likely affected by permafrost thaw-induced changes in hydrogeological processes, which are tightly associated with increases in active layer thickness and enhanced groundwater discharge to rivers. Under a warming climate, riverine solute exports in Arctic rivers are expected to increase with intensifying groundwater-surface water exchanges.