Landscape-gradient assessment of thermokarst lake hydrology using water isotope tracers

Abstract

Please cite this article as: Narancic, B., Wolfe, B.B., Pienitz, R., Meyer, H., Lamhonwah, D., Landscape-gradient assessment of thermokarst lake hydrology using water isotope tracers, Journal of Hydrology (2016), doi: http:// dx.doi.org/10. 1016/j.jhydrol.2016.11.028 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.1 Landscape-gradient assessment of thermokarst lake hydrology using water isotope -Water isotopes are used to characterize thermokarst lake hydrology in Nunavik, Canada.-Rainfall and/or permafrost meltwater are the main lake water sources.-Maritime climate enhances the hydrological resiliency of thermokarst lakes.-Terrestrial carbon inputs from surface runoff are likely to increase in the future.-Thermokarst lakes will persist and methane emissions are likely to increase.3 ABSTRACT Thermokarst lakes are widespread in arctic and subarctic regions. In subarctic Québec (Nunavik), they have grown in number and size since the mid-20 th century.Recent studies have identified that these lakes are important sources of greenhouse gases. This is mainly due to the supply of catchment-derived dissolved organic carbon that generates anoxic conditions leading to methane production. To assess the potential role of climate-driven changes in hydrological processes to influence greenhouse-gas emissions, we utilized water isotope tracers to characterize the water balance of thermokarst lakes in Nunavik during three consecutive mid-to late summer seasons (2012)(2013)(2014). Lake distribution stretches from shrub-tundra overlying discontinuous permafrost in the north to spruce-lichen woodland with sporadic permafrost in the south.Calculation of lake-specific input water isotope compositions ( I ) and lake-specific evaporation-to-inflow (E/I) ratios based on an isotope-mass balance model reveal a narrow hydrological gradient regardless of diversity in regional landscape characteristics. Nearly all lakes sampled were predominantly fed by rainfall and/or permafrost meltwater, which suppressed the effects of evaporative loss. Only a few lakes in one of the southern sampling locations, which overly highly degraded sporadic permafrost terrain, appear to be susceptible to evaporative lake-level drawdown. We attribute this lake hydrological resiliency to the strong maritime climate in coastal regions of Nunavik. Predicted climate-driven increases in precipitation and permafrost degradation will likely contribute to persistence and expansion of thermokarst lakes throughout the region. If coupled with an increase in terrestrial carbon inputs to thermokarst lakes from surface runoff, conditions favorable for mineralizatio...

A synthesis of thermokarst lake water balance in high-latitude regions of North America from isotope tracers

“…Lakes in NUN have roughly equal proportions of rainfall-and snowfall-dominated lakes. Snowfall-dominated lakes from YF also likely include lakes with substantial contributions from permafrost thaw water (and possibly also in NUN, although these are isotopically indistinguishable from rainfall-dominated lakes; Narancic et al 2017). E/I values span from almost 0 to much greater than 1.…”

“…These are included in this synthesis because they constitute a portion of the shallow aquatic ecosystems in these landscapes and for simplicity, we refer to "thermokarst lakes" as all encompassing. Thermokarst lakes from which isotope data have been obtained tend to be shallow and range in surface area (ACP: 0.6-16.2 m, 0.04-9.8 km 2 ; YF: 1-30 m, 0.017-5 km 2 (Anderson et al 2013); OCF: 0.47-4.15 m, 2 × 10 −3 − 13.181 km 2 (Turner et al 2010); HBL: < 0.5 m, < 7 × 10 −4 − 7.6 km 2 (Bouchard et al 2013); NUN: 1-5 m,~1.3 × 10 −6 to 2.1 × 10 −3 km 2 (Bouchard et al 2014;Narancic et al 2017)). A common gridded climate database was used to compile regional meteorological records for comparative purposes, to provide necessary parameters for water isotope mass balance modeling, and to gain insight of meteorological influence on lake water balances.…”

“…Forty-four lakes were sampled during August 2015 in ACP, 149 lakes were sampled once during the summer between 2007 and 2011 in YF (Anderson et al 2013), 53 lakes were sampled each summer from 2007 to 2009 and four additional lakes were sampled in 2007 and 2009 in OCF (Turner et al 2010(Turner et al , 2014, 40 lakes were sampled in the summer of 2010 in HBL and 37 lakes were sampled in the summers of 2011-2012 (Bouchard et al 2013), and 86 lakes were sampled from one to four times during summers 2011-2014 in NUN (Narancic et al 2017). Samples were collected at 10-15 cm water depth in either 30 mL high density polyethylene bottles or 20 mL scintillation vials with plastic cone-shaped caps.…”

“…Slightly more than half of the lakes (52%) in NUN are snowmelt dominated, indicating a more even distribution of snowmelt versus rainfall source waters throughout the landscape. Some rainfalldominated lakes in NUN may also be fed by permafrost thaw waters (Narancic et al 2017). Rainfall-dominated lakes are the overwhelming majority in HBL (80%) and ACP (91%), reflecting the strong influence of rainfall on lake water balances in these landscapes at the time of sampling.…”

“…Specifically, we assemble surface water isotope compositions measured during summers of the past decade from mainly thermokarst lakes across five expansive lake-rich permafrost landscapes. From west to east, these include Arctic Coastal Plain (Alaska) (Arp et al 2015), Yukon Flats (Alaska) (Anderson et al 2013), Old Crow Flats (Yukon) (Turner et al 2010(Turner et al , 2014Tondu et al 2013), western Hudson Bay Lowlands (Manitoba) (Bouchard et al 2013), and Nunavik (Quebec) (Narancic et al 2017). We use isotope-mass balance modeling to determine lake input-water isotope compositions and E/I ratios and explore their relations among landscapes and with environmental drivers.…”