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Permafrost and Rain Influence Summer Hydrologic Flowpaths in Boreal Catchments.

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Title: Permafrost and Rain Influence Summer Hydrologic Flowpaths in Boreal Catchments.
Authors: Jorgenson, Karen L., Douglas, Thomas A., Jorgenson, M. Torre, Pastick, Neal J., Harms, Tamara K.
Source: Water Resources Research; Jun2025, Vol. 61 Issue 6, p1-19, 19p
Subject Terms: GLOBAL warming, STREAM chemistry, RAINSTORMS, WATERSHEDS, SOIL classification
Abstract: Flowpaths of water through catchments influence water quality and flow regimes of streams. Depths of dominant flowpaths respond to variation in climate and catchment characteristics, such as topography, vegetation, and soil type. In high‐latitude regions, the depth and spatial extent of permafrost influences catchment hydrology, and thawing permafrost might change sources and pathways of water supplying solutes and flow to streams. We estimated contributions of precipitation, soil water, and groundwater flowpaths to streams during the open‐water period after snowmelt by applying a Bayesian mixing model to 4–6 years of observed solute concentrations in five catchments of boreal Alaska. The relative contribution of groundwater to streams varied from 12% to 82% across catchments and years and declined as spatial extent of permafrost increased from 25% to 58% across catchments, indicating potential for increased infiltration and drainage as permafrost thaws. Temporal patterns in precipitation also influenced flowpaths. The mean annual contribution of precipitation to streamflow increased in years with more rain. Groundwater contribution increased, on average, in years with few large storms, suggesting deepening flows due to seasonal ground thaw or loss of shallow water to evapotranspiration. In contrast, groundwater contributed less in years when large storms delivered most of the year's rain in late summer or autumn. Overall, spatial and temporal variation in relative flowpath contributions to streams suggest that permafrost thaw will deepen flowpaths, but increasing precipitation expected in high‐latitude regions under warming climate might obscure this effect by routing water via shallow flowpaths following large storms. Plain Language Summary: Permafrost, ground that remains frozen for two or more years, prevents water from infiltrating deep into the ground. In catchments with permafrost, rapid routing of water through shallow soils makes streamflow and solute export highly responsive to precipitation. Catchments with less permafrost could allow water to seep deeper into the ground, causing greater contribution of groundwater to streamflow. We used a mixing model and daily to biweekly observations of stream chemistry to quantify the relative contributions of precipitation, soil water, and groundwater to streamflow. Models were applied to five streams of Interior Alaska with catchments that varied in spatial extent of permafrost and vegetation type. Model results showed that the relative contribution of groundwater to streamflow was greater in catchments with less permafrost. Across the region of spatially discontinuous permafrost, catchments encompassing less permafrost will tend to yield higher concentrations of mineral ions in streamwater. The flowpaths also changed in response to the amount and timing of precipitation, with greater flow through shallow flowpaths contributed by precipitation in wetter years. Increases in rain and storm intensity expected under a warming climate will therefore contribute to periods of more dilute solute concentrations in streams corresponding to shallower flowpaths following storms. Key Points: Mixing models estimated flowpaths contributing solutes to streams in five boreal catchments with varying spatial extent of permafrostIncreased groundwater input with decreasing spatial extent of permafrost showed deeper infiltration and water storage with less permafrostRain increased the contribution of shallow flowpaths, obscuring the effect of permafrost during above‐average rainfall [ABSTRACT FROM AUTHOR]
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Database: Biomedical Index
Description
Abstract:Flowpaths of water through catchments influence water quality and flow regimes of streams. Depths of dominant flowpaths respond to variation in climate and catchment characteristics, such as topography, vegetation, and soil type. In high‐latitude regions, the depth and spatial extent of permafrost influences catchment hydrology, and thawing permafrost might change sources and pathways of water supplying solutes and flow to streams. We estimated contributions of precipitation, soil water, and groundwater flowpaths to streams during the open‐water period after snowmelt by applying a Bayesian mixing model to 4–6 years of observed solute concentrations in five catchments of boreal Alaska. The relative contribution of groundwater to streams varied from 12% to 82% across catchments and years and declined as spatial extent of permafrost increased from 25% to 58% across catchments, indicating potential for increased infiltration and drainage as permafrost thaws. Temporal patterns in precipitation also influenced flowpaths. The mean annual contribution of precipitation to streamflow increased in years with more rain. Groundwater contribution increased, on average, in years with few large storms, suggesting deepening flows due to seasonal ground thaw or loss of shallow water to evapotranspiration. In contrast, groundwater contributed less in years when large storms delivered most of the year's rain in late summer or autumn. Overall, spatial and temporal variation in relative flowpath contributions to streams suggest that permafrost thaw will deepen flowpaths, but increasing precipitation expected in high‐latitude regions under warming climate might obscure this effect by routing water via shallow flowpaths following large storms. Plain Language Summary: Permafrost, ground that remains frozen for two or more years, prevents water from infiltrating deep into the ground. In catchments with permafrost, rapid routing of water through shallow soils makes streamflow and solute export highly responsive to precipitation. Catchments with less permafrost could allow water to seep deeper into the ground, causing greater contribution of groundwater to streamflow. We used a mixing model and daily to biweekly observations of stream chemistry to quantify the relative contributions of precipitation, soil water, and groundwater to streamflow. Models were applied to five streams of Interior Alaska with catchments that varied in spatial extent of permafrost and vegetation type. Model results showed that the relative contribution of groundwater to streamflow was greater in catchments with less permafrost. Across the region of spatially discontinuous permafrost, catchments encompassing less permafrost will tend to yield higher concentrations of mineral ions in streamwater. The flowpaths also changed in response to the amount and timing of precipitation, with greater flow through shallow flowpaths contributed by precipitation in wetter years. Increases in rain and storm intensity expected under a warming climate will therefore contribute to periods of more dilute solute concentrations in streams corresponding to shallower flowpaths following storms. Key Points: Mixing models estimated flowpaths contributing solutes to streams in five boreal catchments with varying spatial extent of permafrostIncreased groundwater input with decreasing spatial extent of permafrost showed deeper infiltration and water storage with less permafrostRain increased the contribution of shallow flowpaths, obscuring the effect of permafrost during above‐average rainfall [ABSTRACT FROM AUTHOR]
ISSN:00431397
DOI:10.1029/2024WR039024