Arctic Science Impact of permafrost thaw on the turbidity regime of a subarctic river: the Sheldrake River, Nunavik, Quebec Journal: Arctic Science Manuscript ID AS-2016-0006.R3 Manuscript Type: Article Date Submitted by the Author: 26-Apr-2017 Complete List of Authors: Jolivel, Maxime; centre d'études nordiques, géographie Allard, Michel; Université Laval, Centre d'études nordiques Keyword: permafrost,Draft Northern Quebec, thermokarst, turbidity, subarctic river https://mc06.manuscriptcentral.com/asopen-pubs Page 1 of 56 Arctic Science 1 Impact of permafrost thaw on the turbidity regime of a subarctic river: the 2 Sheldrake River, Nunavik, Quebec. 3 Maxime Jolivel and Michel Allard 4 5 M. Jolivel and M. Allard, Centre d’études nordiques (CEN) and Département de 6 Géographie, Université Laval, Québec QC, G1V 0A6 Canada. 7 Corresponding author: [email protected] 8 9 Draft 10 11 12 13 14 15 16 17 18 19 20 21 1 https://mc06.manuscriptcentral.com/asopen-pubs Arctic Science Page 2 of 56 22 Abstract 23 In order to assess the impact of seasonal active layer thaw and thermokarst on 24 river flow and turbidity, a gauging station was installed near the mouth of the Sheldrake 25 River in the discontinuous permafrost zone of Northern Quebec. The station provided 26 five years of water level data and three years of turbidity data. The hydrological data for 27 the river showed the usual high water stage occurring at spring snow melt, with smaller 28 peaks related to rain events in summer. Larger and longer turbidity peaks also occurred in 29 summer in response to warm air temperature spells suggesting that a large part of the 30 annual suspension load was carried during mid-summer turbidity peaks. Supported by 31 geomorphological observations acrossDraft the catchment area, the most plausible 32 interpretation is that the rapid thawing of the active layer during warm conditions in July 33 led to the activation of frostboils and triggered landslides throughout the river catchment, 34 thus increasing soil erosion and raising sediment delivery into the hydrological network. 35 These results indicate that maximum sediment discharge in a thermokarst-affected region 36 may be predominantly driven by the rate of summer thawing and associated activation of 37 erosion features in the catchment. 38 Keywords: permafrost, Northern Quebec, thermokarst, turbidity, subarctic river 39 Introduction 40 Rivers are natural pathways from land to sea that carry sediments and other matter 41 eroded from their catchments. Their behavior reflects different geomorphic and 42 biogeochemical processes in the landscape with cascading effects downstream to the 2 https://mc06.manuscriptcentral.com/asopen-pubs Page 3 of 56 Arctic Science 43 coastal marine environment. In the context of climate change, river studies are essential 44 to quantify the pace and intensity of geosystem changes (Prowse et al. 2015). In subarctic 45 regions, the riverine hydrological regime is strongly linked to seasonal climate variations, 46 which generate a large annual range in water discharge (Déry et al. 2005). Sediment loads 47 can also be extremely variable even if they are sometimes low in comparison with rivers 48 from temperate and tropical regions (Syvitski 2002). 49 The hydrological cycle of high latitude rivers is regulated by snow storage and 50 melting and by the freezing of soil water. Permafrost is a major factor that restricts 51 infiltration and percolation at depth; a perched water table is maintained in the active 52 layer near the surface in summer (Carey and Woo 2001; Carey and Quinton 2005; 53 Quinton and Carey 2008). BaseDraft flow may cease in winter since sub-permafrost 54 groundwater may be non-existent or too deep to discharge in the catchment and because 55 taliks can be only poorly connected with springs on the river beds. Soil warming, 56 thinning and decay of permafrost, earlier breakups, decline of snow cover duration and 57 increase in shrub, forest and peatland covers are factors affecting the hydrology of high 58 latitude rivers under ongoing climate change (Magnuson et al. 2000; Sturm et al. 2001; 59 Payette et al. 2004; Brown and Romanovsky 2008; Jolivel and Allard 2013; Lesack et al. 60 2014). For example, it is broadly expected that the sediment load of high latitude rivers 61 would increase by 30% for every 2 °C of warming of the averaged catchment temperature 62 (Syvitski 2002). 63 Thawing of permafrost is known to release large volumes of sediments through 64 thermokarst processes such as thaw slumping and thermal erosion (Jolivel and Allard 65 2013; Kokelj et al. 2013). The released sediments are mobilized by soil erosion, in 3 https://mc06.manuscriptcentral.com/asopen-pubs Arctic Science Page 4 of 56 66 overland flow and in water courses; they feed sedimentation (Guo et al. 2004; Goni et al. 67 2005; Jolivel et al. 2015) and get involved in biogeochemical processes (Emmerton et al. 68 2008; Galand et al. 2008; Vonk et al. 2015) in lakes, deltas and coastal seas. 69 Evidence of general permafrost decay has been observed throughout all high- 70 latitude regions (e.g. Sollid and Sorbel 1998; Luoto and Seppälä 2003; Jorgenson et al. 71 2006). In northern Québec, near the southern limit of permafrost distribution, thawing of 72 permafrost in large areas of palsas, lithalsas, peat plateaus and permafrost plateaus has 73 led to the reduction of permafrost extent by roughly 40% over the last 50 years (Payette 74 et al. 2004; Marchildon, 2007; Vallée and Payette 2007; Fortier and Aubé-Maurice 2008; 75 Jolivel and Allard, 2013). ContinuedDraft warming will lead to further degradation, releasing 76 sediments and making previously frozen organic matter available for bacterial 77 decomposition and recycling into bio-available carbon and greenhouse gases (Schuur et 78 al. 2008; Deshpande et al. 2015; Vonk et al. 2015). 79 Thermokarst and associated landslides generate large sediment loads in rivers. 80 This is particularly evident in the case of retrogressive thaw slumps and large active layer 81 detachment slides (Kokelj et al. 2002; Lewis et al. 2005; Lewkowicz and Harris 2005a; 82 Jorgenson et al. 2006; Lantuit and Pollard 2008; Lantz and Kokelj 2008; Lamoureux and 83 Lafrenière 2009; Lacelle et al. 2010; Kokelj et al. 2013). These inputs can alter terrestrial 84 and aquatic ecosystems and affect food webs as well as primary and secondary 85 production (Kokelj et al. 2002, 2009; Bowden et al. 2008; Mesquita et al. 2010). 86 Ultimately, a significant fraction of the organic carbon released by thermokarst may 87 reach the marine environment (Jolivel et al. 2015; Vonk et al. 2015). 4 https://mc06.manuscriptcentral.com/asopen-pubs Page 5 of 56 Arctic Science 88 More gauging of rivers and monitoring of processes are necessary to understand 89 the sedimentary regime of rivers in regions affected by thermokarst. This is particularly 90 true during periods of significant temporal change in fluvial fluxes resulting from 91 seasonal variations of thermokarst processes in response to climate forcing (Prowse et al. 92 2015). There are few measurements of the impacts of eroding permafrost catchments on 93 fluvial sedimentary regimes (Bowden et al. 2008), and more data are required to better 94 understand geomorphological processes in these regions in transition. 95 The main objectives of this study were to (1) document the annual and seasonal 96 hydrologic fluctuations of a Subarctic river; (2) describe the dynamics of turbidity and 97 sediment fluxes during the thawing season; and (3) assess the relative impacts of 98 precipitation and thawing on dischargeDraft and sediment transport. Because the rate of soil 99 thawing influences the rate of thermokarst which releases sediments in the drainage 100 network, we raised the hypothesis that variations in air temperature can influence 101 turbidity of surface water, and so the amount and timing of sediment fluxes in the 102 collector river. 103 104 Methods 105 Study area 106 The 25 km long Sheldrake River flows to the eastern coast of Hudson Bay. It 107 drains a 76 km 2 watershed (Fig. 1). Its catchment is typical of the area of decaying 108 sporadic/discontinuous permafrost in the Tyrrell sea fine sediments of Eastern Hudson 109 Bay. The Sheldrake is among many rivers of the east Hudson Bay watershed, including 110 large fluvial systems such as the Nastapoka River that transport sediment resulting from 5 https://mc06.manuscriptcentral.com/asopen-pubs Arctic Science Page 6 of 56 111 erosional, thermokarst and periglacial processes (Fig. 2).Typically, in summer conditions, 112 the river varies in width from 25 to 50 m. Its depth varies between 3 m in water pools to 113 50 cm in rapids. In the upper part of the river, the river bed is generally composed of a 114 thin veneer of sand and gravel covering thick marine silty clay. From its passage in the 115 coastal hills to the shore, the bed and the banks are essentially composed of exposed 116 bedrock and boulders, which greatly limits bed load transport. 117 The river originates from Sheldrake Lake, on the Archean sector of the Canadian 118 Shield. Near the coast, the river valley runs across a range of coastal hills in Late 119 Proterozoic bedrock and the river flows into Hudson Bay at 56°37’N; 76°32’W (Fig. 1). 120 On a topographic 1:50,000 map, the low-gradient Sheldrake River is a third order stream. 121 However, the rapid and recent permafrostDraft decay increased the hydrologic connectivity 122 between thermokarst ponds, hollows and gullies thereby increasing stream density 123 (Jolivel and Allard 2013). 124 The east-west elongated shape of the catchment (Gravelius index: 1.9; Gravelius 125 1914) is principally due to the carving activity of the Pleistocene glaciers that flowed to 126 the west.