Active layer slope disturbances affect seasonality and composition of dissolved nitrogen export from High Arctic headwater catchments

Lafrenière, Melissa J.; Louiseize, Nicole L.; Lamoureux, Scott F.

doi:10.1139/as-2015-0009

Cited by 19 publications

(22 citation statements)

References 71 publications

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“…Permafrost soils, however, contain high levels of biologically available N in deeper, perennially frozen layers (Finger et al, 2016;Keuper et al, 2012;Wild et al, 2013), and thawing landscapes are associated with increased transport of N from soils to streams (Abbott et al, 2015;Bowden et al, 2008;Harms & Jones, 2012). There is evidence that plants access more N during permafrost thaw (Keuper et al, 2017;Lafrenière et al, 2017;Salmon et al, 2016;Schuur et al, 2007), but the location, timing, and magnitude of increased N availability in warming tundra profiles are not well documented, and plant uptake from deep N pools is not included in current Earth system models (Koven et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Adding Depth to Our Understanding of Nitrogen Dynamics in Permafrost Soils

et al. 2018

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Losses of C from decomposing permafrost may be offset by increased productivity of tundra plants, but nitrogen availability partially limits plant growth in tundra ecosystems. In this soil incubation experiment carbon (C) and nitrogen (N) cycling dynamics were examined from the soil surface down through upper permafrost. We found that losses of CO2 were negatively correlated to net N mineralization because C‐rich surface soils mineralized little N, while deep soils had low rates of C respiration but high rates of net N mineralization. Permafrost soils released a large flush of inorganic N when initially thawed. Depth‐specific rates of N mineralization from the incubation were combined with thaw depths and soil temperatures from a nearby manipulative warming experiment to simulate the potential magnitude, timing, and depth of inorganic N release during the process of permafrost thaw. Our calculations show that inorganic N released from newly thawed permafrost may be similar in magnitude to the increase in N mineralized by warmed soils in the middle of the profile. The total release of inorganic N from the soil profile during the simulated thaw process was twice the size of the observed increase in the foliar N pool observed at the manipulative experiment. Our findings suggest that increases in N availability are likely to outpace the N demand of tundra plants during the first 5 years of permafrost thaw and may increase C losses from surface soils as well as induce denitrification and leaching of N from these ecosystems.

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Section: Introductionmentioning

confidence: 99%

Adding Depth to Our Understanding of Nitrogen Dynamics in Permafrost Soils

et al. 2018

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“…After carbon composition, nutrient status was the second most important factor explaining BDOC on the Peel Plateau (Table ). Thermokarst features are well documented to release nutrients, particularly inorganic nitrogen (Bowden et al, ; Harms & Jones, ; Lafreniére et al, ; Louiseize et al, ; Reyes et al, ). Outside of permafrost‐affected regions, an increase in BDOC has been recorded in incubation experiments subject to nutrient additions (Marschner & Kalbitz, ; McDowell et al, ).…”

Section: Discussionmentioning

confidence: 99%

Biodegradability of Thermokarst Carbon in a Till‐Associated, Glacial Margin Landscape: The Case of the Peel Plateau, NWT, Canada

Littlefair

Tank

2018

JGR Biogeosciences

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The Peel Plateau is a characteristic glacial margin landscape, with permafrost comprised of thick, ice-rich glacial tills deposited at the end of the Last Glacial Maximum. Unmodified tills at depth are overlain by a paleo-active layer, created when early Holocene warming deepened regional active layers, enabling organic matter incorporation into now-frozen soils. Ice-rich permafrost encourages retrogressive thaw slumps, which mobilize variable proportions of modern active layer, paleo-active layer, and Pleistocene tills to downstream systems. Here we investigate the biolability of thaw-released dissolved organic carbon (DOC) on the Peel Plateau and compare our results to previous studies from nontill-dominated landscapes. Similar to other Arctic regions, biolability was significantly greater for slump-derived DOC (retrogressive thaw slump runoff) than for DOC from paired, unimpacted locations. However, runoff source was an important control on biolability. Lability was greater for slumps releasing water with a Holocene-like δ 18 O signature than for slumps with a more Pleistocene-like signature, while a small slump, with runoff δ 18 O similar to the modern active layer, showed no biolability increase. Similar to other Arctic regions, biolability was strongly related to DOC aromaticity and molecular weight. However, lability also increased significantly with increasing nutrients, which has not been shown universally. Previous work has shown that DOC concentration dynamics differ sharply on the Peel Plateau when compared to other permafrost thaw landscapes. This work indicates that the lability of permafrost DOC may be relatively uniform across variable Arctic regions, although some factors-such as the importance of nutrient status-may need further exploration.LITTLEFAIR AND TANK 3293

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“…High concentrations remained in both disturbed and undisturbed subcatchments and show high interannual variability. Additionally, deep thaw in 2011 and 2012 (without physical disturbance) appears to have sustained higher solute loads, resulting in a situation where solute fluxes remain high and characterized by high interannual variability, 24,32 while sedimentary fluxes have diminished considerably 29 (Figure 8). Thermal perturbation appears to have increased availability of dissolved solids, resulting in both higher concentrations and fluxes, but also a heightened sensitivity to summer rainfall events.…”

Section: Permafrost Degradation and Disturbance Impacts And Recoverymentioning

confidence: 99%

“…Changes to nitrogen flux from catchments show high interannual variability and suggest further retention within the fluvial systems. 43 Additionally, permafrost disturbance and degradation appears to substantially alter the downstream delivery of nitrate and ammonium 32,33 ).…”

Section: Downstream Linkages and Cumulative Effectsmentioning

confidence: 99%

“…In the disturbed Ptarmigan subcatchment, solute loads increased by 57% between pre‐disturbance 2007 and post‐disturbance 2008 seasons, and a larger network of measurements in 2008 and 2009 showed continued increases in disturbed catchments. Nitrate concentrations were notably higher in disturbed Ptarmigan subcatchment and NO 3 − ‐δ 15 N analysis suggests enhanced microbial nitrification was responsible . Increased total dissolved solid concentrations scaled linearly with the percent area of the catchment that was disturbed, but catchment yields appeared to reach maximum at approximately 15–20% disturbance area .…”

Section: Introductionmentioning

confidence: 96%

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More than just snowmelt: integrated watershed science for changing climate and permafrost at the Cape Bounty Arctic Watershed Observatory

Lamoureux

Lafrenière

2017

WIREs Water

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The Cape Bounty Arctic Watershed Observatory (CBAWO) was established in 2003 to investigate the hydrological processes and impacts associated with climate and permafrost change in the High Arctic. Comprehensive data collection at the paired watersheds has spanned a period containing both the coldest and warmest melt season conditions, including the recent decade that is the warmest on record. Through this period, the hydrological regime has transitioned from a nival (snowmelt) dominated to increased importance of rainfall runoff and baseflow. This hydrological shift and associated environmental changes have altered the seasonality and magnitude of fluxes. Permafrost degradation has resulted in both localized and catchment-wide soil and runoff perturbations, broadly increasing solute and nutrient flushing, with more intense sediment and solute impacts where physical disturbances have occurred. The recovery time to perturbations diverges with sedimentary systems responding in approximately 5 years, while dissolved fluxes remaining high due to repeated thermal perturbations. Permafrost carbon in this setting is relatively old and labile, both in particulate and dissolved phases. Permafrost degradation has altered microbial activity in soils, and increased nitrification in disturbed settings, which points to complex biogeochemical responses to climate and permafrost change. Sustained research activity at CBAWO has revealed new complexity in the hydrological and biogeochemical functioning of High Arctic watersheds. Long-term observatories like CBAWO provide critical context to place observations in, especially during periods of change, and are necessary to develop a comprehensive understanding of hydrological change and water security in the region.

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Active layer slope disturbances affect seasonality and composition of dissolved nitrogen export from High Arctic headwater catchments

Cited by 19 publications

References 71 publications

Adding Depth to Our Understanding of Nitrogen Dynamics in Permafrost Soils

Adding Depth to Our Understanding of Nitrogen Dynamics in Permafrost Soils

Biodegradability of Thermokarst Carbon in a Till‐Associated, Glacial Margin Landscape: The Case of the Peel Plateau, NWT, Canada

More than just snowmelt: integrated watershed science for changing climate and permafrost at the Cape Bounty Arctic Watershed Observatory

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