The Cold Vadose Zone: Hydrological and Ecological Significance of Frozen‐Soil Processes

Abstract

Approximately 50% of soils in the Northern Hemisphere experience seasonal freezing and thawing, which influences physical, chemical, and biological processes in the vadose zone. Soil freeze–thaw drives mechanical processes, including frost heave and soil aggregate formation and breakdown, and controls snowmelt infiltration and runoff. These hydrologic processes determine the soil moisture conditions, which affect plant mortality and growth, soil microbial activities, and nutrient (e.g., C and N) cycles. Nutrients leached from the thawed soil, often with rapid infiltration of snowmelt water, may affect the quality of the groundwater and surface water, in combination with enhanced erosion and sediment load due to freeze–thaw. Nutrients released as greenhouse gases may contribute to climate feedback. With recent climate warming and changes in the extent and depth of frozen soil and permafrost, it is important to understand frozen‐soil processes and their interaction with the environment. The objective of this review is to highlight important aspects of soil freeze–thaw and related processes and to point out research challenges and opportunities in the cold vadose zone.

Infiltration into frozen soil: From core‐scale dynamics to hillslope‐scale connectivity

“…These hydrological variables all have their own spatial distribution at the hillslope scale and specific effects on patterns of ponding and run‐off generation, that is, hydrological connectivity. These effects obscure the singular control of the frozen aspect of soil on run‐off response and infiltration distribution (Hayashi, ) and are the main reason why application of point‐scale understanding of infiltration into frozen soil to prediction at the hillslope‐ and catchment‐scales has been so difficult.…”

Contrasting hydrogeologic responses to warming in permafrost and seasonally frozen ground hillslopes

“…In areas with continuous permafrost, permafrost's low permeability prevents deep groundwater flow while increasing groundwater discharge to the shallow subsurface ( Figure 1b) . In contrast, in regions underlain by only SFG, seasonal freezing of the subsurface influences infiltration [Hayashi, 2013] and causes seasonal variations in groundwater flow with both shallow and deep groundwater flow paths present in the warmer months ( Figure 1d) [Woo et al, 2008].…”

Effects of antecedent moisture and macroporosity on infiltration and water flow in frozen soil

“…In many cold regions, meltwater infiltration into frozen ground plays a key role in watershed response during snowmelt periods by controlling the partitioning of water at the land surface (Hayashi, 2013;Ireson, van der Kamp, Ferguson, Nachshon, & Wheater, 2013). Frozen soil infiltration dynamics are governed by complex, coupled water and energy transfers near ground surface, which are strongly affected by pre-freezing meteorological and soil moisture conditions (Granger, Gray, & Dyck, 1984;Stähli, Jansson, & Lundin, 1999).…”