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Ice Wedge Degradation and CO2 and CH4 Emissions in the Tuktoyaktuk Coastlands, NT

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Ice Wedge Degradation and CO2 and CH4 Emissions in the Tuktoyaktuk Coastlands, NT Arctic Science Ice wedge degradation and CO2 and CH4 emissions in the Tuktoyaktuk Coastlands, NT Journal: Arctic Science Manuscript ID AS-2016-0011.R2 Manuscript Type: Article Date Submitted by the Author: 11-Aug-2017 Complete List of Authors: Martin, Abra; University of Victoria, School of Environmental Studies Lantz, Trevor; University of Victoria, Environmental Studies Humphreys, Elyn; Carleton University , Geography and Environmental Studies Draft Keyword: carbon dioxide, methane, permafrost, thermokarst, ice wedge Is the invited manuscript for consideration in a Special N/A Issue?: https://mc06.manuscriptcentral.com/asopen-pubs Page 1 of 37 Arctic Science Ice wedge degradation and CO 2 and CH 4 emissions in the Tuktoyaktuk Coastlands, NT. Abra F. Martin 1, Trevor C. Lantz 1,3 and Elyn R. Humphreys 2 1. School of Environmental Studies, University of Victoria 2. Geography and Environmental Studies, Carleton University 3. Author for Correspondence: [email protected] 4. AFM and TCL conceived the study; AFM and TCL collected the data; AFM analyzed the data; AFM,Draft TCL and ERH wrote the manuscript. https://mc06.manuscriptcentral.com/asopen-pubs Arctic Science Page 2 of 37 1 Abstract 2 3 Increases in ground temperature make soil organic carbon in permafrost 4 environments highly vulnerable to release to the atmosphere. High-centred polygonal 5 terrain is a form of patterned ground that may include areas that act as large sources of 6 carbon to the atmosphere because thawing ice-wedges can result in increased ground 7 temperatures, soil moisture and thaw depth. To evaluate the effect of ice wedge 8 degradation on carbon flux, carbon emissions were characterized at two polygonal 9 peatlands in the Tuktoyaktuk Coastlands in northern Canada. Opaque chambers were 10 used to measure CO 2 and CH 4 emissions from nine non-degraded polygon centres and 11 nine moderately-degraded troughsDraft four times during the growing season. To measure 12 emissions from 10 ponds resulting from severe ice wedge degradation, wind diffusion 13 models were used to characterize fluxes using CO 2 and CH 4 measurements made in each 14 pond. Our field data show that degraded troughs had increased ground temperature, 15 deeper active layers, and increased CO 2 and CH 4 emissions. Our study shows that rates of 16 CO 2 and CH 4 emissions from high-centered polygonal terrain are likely to increase with 17 more widespread melt pond formation in this terrain type. 18 19 Key words: carbon dioxide, methane, permafrost, thermokarst https://mc06.manuscriptcentral.com/asopen-pubs Page 3 of 37 Arctic Science 20 Introduction 21 22 Permafrost soils hold large quantities (1140-1476Pg) of soil organic carbon 23 (SOC) (Hugelius et al. 2014). Ongoing changes in temperature and precipitation are 24 likely to alter carbon cycling in Arctic and subarctic ecosystems (Oechel et al. 1993; 25 Schuur et al. 2008; Grosse et al. 2011) and thawing permafrost in the circumpolar region 26 could release between 37-174 Pg of carbon to the atmosphere by 2100. It is estimated that 27 the permafrost carbon feedback could result in an additional 0.42 °C of warming by 2300 28 (Schuur et al. 2015). 29 High-centred polygonal terrain is one of the most common forms of patterned 30 ground in the Low Arctic. This Draftterrain type is characterized by thick organic deposits and 31 large ice wedges (Zoltai and Tarnocai 1975; Vardy et al. 1997). Elevated polygon centres 32 are surrounded by low-lying troughs underlain by ice wedges, which form a characteristic 33 polygonal network when viewed from the above (Fig. 1) Common in low-lying lacustrine 34 basins across the Arctic, high-centred polygon terrain is likely to be particularly sensitive 35 to climate warming because the ground ice content is high (Kokelj et al. 2014). When 36 ice-wedges degrade, the ground subsides, polygon troughs become wetter, and active 37 layer thickness and mean annual ground temperature increase (Jorgenson et al. 2015). 38 Moderate trough degradation is characterized by some subsidence, increased moisture 39 and the presence of sedges (Fig. 1). Terrain subsidence associated with severe ice-wedge 40 degradation results in the formation of melt pondsthat do not support rooted plants (Fig. 41 1). The volume and depth of water in these ponds may extend the duration of freeze-back 42 and in some locations the underlying soil may not freezeback over winter (Kokelj et al. https://mc06.manuscriptcentral.com/asopen-pubs Arctic Science Page 4 of 37 43 2014). Several recent studies show that ice wedge degradation in high-centered polygonal 44 terrain is increasing the number and size of melt ponds at sites across the Arctic 45 (Liljedahl et al. 2016; Jorgenson et al. 2015; Raynolds et al. 2014; Steedman et al. 2016). 46 Increased ice wedge degradation has the potential to affect 10-30% of Arctic 47 lowlands (Jorgenson et al. 2006) and the changes in soil moisture that accompany 48 degradation are likely to have a significant impact on carbon cycling (Schuur et al. 2008; 49 Lee et al. 2010; Kokelj and Jorgenson 2013). As ice wedges degrade, adjacent soils 50 become saturated and aerobic decomposition processes may become limited as diffusion 51 of oxygen belowground is restricted (Funk et al. 1994; Davidson and Janssens 2006; 52 Schlesinger and Bernhardt 2013). Anaerobic conditions are likely to promote methane 53 (CH 4) production (Schlesinger andDraft Bernhardt 2013). Other studies have shown that small 54 water bodies can have substantial emission rates for both CO 2 and CH 4 (Bouchard et al. 55 2015). With the formation of melt ponds in severely degraded ice-wedges, microbial 56 activity in the water column and the soils underlying the ponds may promote emissions of 57 both CO 2 and CH 4 via diffusion or ebullition to the surface (Laurion et al. 2010). In this 58 research we tested the hypothesis that ice wedge degradation results in larger summer 59 emissions of both CO 2 and CH 4 by emissions from severely degraded troughs (melt 60 ponds), moderately degraded troughs (wet troughs) and non-degraded areas (polygon 61 centres). The resulting increased temperature, moisture, thaw depths and substrate 62 availability from degradation will result in both increased anaerobic CO 2 and CH 4 63 production. 4 https://mc06.manuscriptcentral.com/asopen-pubs Page 5 of 37 Arctic Science 64 Methods 65 66 Study Area 67 This study was carried out in the Tuktoyaktuk Coastlands in the Western 68 Canadian Arctic (Fig. 2). This area is characterized by gentle topography and thousands 69 of small lakes (Rampton 1988). Between 30 and 25 ka B.P., the Tuktoyaktuk Coastlands 70 were covered by the Laurentide ice sheet (Duk-Rodkin and Lemmen 2000). As this ice 71 sheet receded, numerous lakes formed and then subsequently drained during the 72 Holocene (Murton 1996). Today approximately 10 % of the Tuktoyaktuk Coastlands are 73 occupied by small basins that host high-centred polygon terrain underlain by thick peat 74 deposits (Steedman et al. 2016; DraftZoltai and Tarnocai 1975; Vardy et al. 1997). 75 The contemporary climate of this region is characterized by mean annual air 76 temperatures of -9.0 °C at Inuvik and -10.2 °C at Tuktoyaktuk and temperatures are 77 typically below freezing from October to April (Environment Canada 2015). In the 78 summer, there is a strong latitudinal temperature gradient across the Tuktoyaktuk 79 Coastlands with average growing season air temperatures (1970-2005) being 3.3°C 80 warmer in Inuvik than Tuktoyaktuk (Lantz et al. 2010a). There is also a precipitation 81 gradient with Tuktoyaktuk receiving a mean total annual precipitation (1970-2006) of 82 166.1 mm, and Inuvik receiving 254.8 mm (Environment Canada 2015). Between 1926 83 and 2006 mean annual air temperatures at Inuvik increased by 1.9 °C (Lantz and Kokelj, 84 2008). This increase in air temperature has been mirrored by an increase in ground 85 temperature of 1.5-2.5 °C since 1970 (Burn and Kokelj 2009). https://mc06.manuscriptcentral.com/asopen-pubs Arctic Science Page 6 of 37 86 The regional climate gradient is accompanied by two transitions in the dominant 87 vegetation. In the southern part of the study area, open spruce woodlands transition into 88 tundra dominated by upright shrubs ( Salix spp., Alnus viridis Chaix. and Betula 89 glandulosa Michx.) Towards the northern end of our study area, upright shrub tundra is 90 replaced by dwarf shrub tundra dominated by ericaceous shrubs and sedges 91 (Rhododendron subarcticum Harmaja (G.D. Wallace) , Vaccinium vitis-ideae L., Carex 92 spp. and Eriophorum spp.) (Lantz et al. 2010b). 93 94 Study Sites 95 96 The effect of ice wedge Draftdegradation on soil respiration was measured at a 97 subarctic site near the community of Inuvik, NT (68°18′55.67″N, 133°25′53.51″W) and 98 an Arctic site near Tuktoyaktuk, NT (69°21′58.08″N, 133°2′6.29″W). Each site was 99 located in an area with high-centred polygons dominated by dwarf shrubs ( Betula 100 glandulosa Michx. , Rhododendron subarcticum Harmaja (G.D. Wallace) , Vaccinium 101 vitis-idaea L. , Vaccinium uliginosum L. , Empetrum nigrum L.), sedges ( Eriophorum spp., 102 Carex aquatilis Wahlenb.) and lichen. Both sites had areas differentially affected by 103 degradation. We classified these areas as: 1) non-degraded areas without ice wedges 104 (polygon centres), 2) moderately degraded ice wedges (wet troughs), and 3) highly 105 degraded ice wedges (melt ponds) (Fig. 1). Polygon centres were characterized by 106 terricolous lichen, Rubus chamaemorus L. , Rhododendron subarcticum Harmaja (G.D. 107 Wallace) and Vaccinium vitis-idaea L. Wet troughs had standing water up to 10 cm deep 108 and were typically dominated by Carex aquatilis Wahlenb.
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