Abstract
Abstract. Ice-wedge polygons are common Arctic landforms. The future of these landforms in a warming climate depends on the bidirectional feedback between the rate of ice-wedge degradation and changes in hydrological characteristics. This work aims to better understand the relative roles of vertical and horizontal water fluxes in the subsurface of polygonal landscapes, providing new insights and data to test and calibrate hydrological models. Field-scale investigations were conducted at an intensively instrumented location on the Barrow Environmental Observatory (BEO) near Utqiaġvik, AK, USA. Using a conservative tracer, we examined controls of microtopography and the frost table on subsurface flow and transport within a low-centered and a high-centered polygon. Bromide tracer was applied at both polygons in July 2015 and transport was monitored through two thaw seasons. Sampler arrays placed in polygon centers, rims, and troughs were used to monitor tracer concentrations. In both polygons, the tracer first infiltrated vertically until encountering the frost table and was then transported horizontally. Horizontal flow occurred in more locations and at higher velocities in the low-centered polygon than in the high-centered polygon. Preferential flow, influenced by frost table topography, was significant between polygon centers and troughs. Estimates of horizontal hydraulic conductivity were within the range of previous estimates of vertical conductivity, highlighting the importance of horizontal flow in these systems. This work forms a basis for understanding complexity of flow in polygonal landscapes.
Highlights
A mechanistic understanding of the feedbacks between Arctic climate and terrestrial ecosystems is critical to understand and predict future changes in these sensitive ecosystems
To better understand the response of the polygons to precipitation inputs, we focused on the temporal characteristics of water level changes caused by 14 precipitation events occurring over the 2015 and 2016 thaw seasons (Fig. 5)
Our study provides new insight into hydrological processes of low- and high-centered polygon systems, where flow and transport field investigations are almost totally lacking
Summary
A mechanistic understanding of the feedbacks between Arctic climate and terrestrial ecosystems is critical to understand and predict future changes in these sensitive ecosystems. Permafrost degradation is of primary concern in the Arctic, as it affects hydrology (Jorgenson et al, 2010; Liljedahl et al, 2011; Zona et al, 2011a), biogeochemical transformations (Heikoop et al, 2015; Lara et al, 2015; Newman et al, 2015), and human infrastructure (Andersland et al, 2003; Hinzman et al, 2013). Wales et al.: Understanding the relative importance of flow zone covers 24 % of the landmass in the Northern Hemisphere and stores an estimated 1.7 billion tons of organic carbon (Hugelius et al, 2013; Schuur et al, 2008, 2015; Tarnocai et al, 2009; Zimov et al, 2006), with a significant fraction stored in the Arctic tundra, where ice-wedge polygons are among the most prolific geomorphological features (Hussey and Michelson, 1966). The degree of soil saturation influences whether carbon is released as carbon dioxide or methane, highlighting the importance of understanding the hydrology of permafrost regions
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