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Climate warming and permafrost thaw induced land cover change are well documented in much of the circumpolar north. The extensive exposure of Precambrian continental crust in Canada's Taiga Shield ecoregion could mean impacts of land cover change documented in other regions without this feature are not transferable. This study examined energy partitioning with eddy covariance measurements, vegetation water use with stable isotopes and soil water state with time domain reflectometry sensors in conifer stands in the Taiga Shield ecoregion. The goal was to determine how changes in forest density with climate warming could influence water budget response and soil water state. Paired measurements of sensible and latent heat imply evaporative processes in denser canopies are controlled more by radiative than the aerodynamic factors predominant in sparser canopies. As denser canopies become more prevalent on the landscape, this switch in relative importance of evapotranspirative processes will lead to a reduction in inter‐annual variability of evapotranspiration. The dominant tree species (black spruce, tamarack and jack pine) were all quick to draw water from shallow soils after spring thaw and rainfall. Stand structural changes resulted in older, more evaporatively enriched water prevalent in soils below dense canopies. While there is evidence for forest infilling, widespread lakes and exposed bedrock restricts extensive expansion of forested land covers. The insufficient difference between sparse and dense canopy evapotranspiration suggest a fundamental change in how water cycles in Taiga Shield catchments is unlikely, which is notably different than previously investigated landscapes in Alaska and the Canadian Taiga Plains. Key Points: Evapotranspiration becomes less sensitive to precipitation variability as canopy density increases in Taiga Shield forestsTaiga vegetation tends to draw younger less evaporatively enriched soil water, and denser forests tend to have older more evaporatively enriched water in soils by the end of the growing seasonIncreased forest cover is not expected to change catchment water cycles because open water and exposed bedrock restrict tree expansion [ABSTRACT FROM AUTHOR]

On the Qinghai-Tibet Plateau, permafrost degradation and associated release of permafrost meltwater has undoubtedly modified the annual and seasonal streamflow patterns and influenced groundwater conditions. However, it is still unclear how extensively permafrost degradation has influenced surface and subsurface water systems due to very sparse observations. Isotope mass models combining tritium and 222Rn measurements are developed here to quantify the contributions of groundwater discharge and thawing permafrost to rivers and lakes in the Source Area of the Yellow River. Results demonstrate the spatial variability of permafrost thaw impacts and confirm significant influence on surface and subsurface runoff processes including effects on water yield capacity and water drainage connectivity. While results to date are conclusive, further work to refine the method and extend observations is warranted. [ABSTRACT FROM AUTHOR]

Tritium concentrations were measured in a survey of 24 lakes, 15 wetlands, and 133 groundwaters in the oil sands region of northeastern Alberta and compared with both recent precipitation and precipitation sampled during the 1960s tritium peak caused by atmospheric thermonuclear weapons testing. Water samples from lakes included a group of 14 thaw lakes that had higher runoff attributed to melting of permafrost in peat plateaus within their watersheds. While tritium in all lakes was found to be intermediate between recent and 1960s concentrations, the thaw lakes were found to be significantly enriched in tritium compared with other lakes, as were unfrozen wetlands characterized by a thick sequence of low-hydraulic conductivity peat. The results provide further evidence of different water sources to the thaw lakes and may indicate that melting of modern permafrost in part formed since the 1950s is occurring in these systems. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]