Degradation changes stable carbon isotope depth profiles in palsa peatlands

Abstract

Abstract. Palsa peatlands are a significant carbon pool in the global carbon cycle and are projected to change by global warming due to accelerated permafrost thaw. Our aim was to use stable carbon isotopes as indicators of palsa degradation. Depth profiles of stable carbon isotopes generally reflect organic matter dynamics in soils with an increase of δ13C values during aerobic decomposition and stable or decreasing δ13C values with depth during anaerobic decomposition. Stable carbon isotope depth profiles of undisturbed and degraded sites of hummocks as well as hollows at three palsa peatlands in northern Sweden were used to investigate the degradation processes. The depth patterns of stable isotopes clearly differ between intact and degraded hummocks at all sites. Erosion and cryoturbation at the degraded sites significantly changes the stable carbon isotope depth profiles. At the intact hummocks the uplifting of peat material by permafrost is indicated by a turning in the δ13C depth trend, and this assessment is supported by a change in the C / N ratios. For hollows isotope patterns were less clear, but some hollows and degraded hollows in the palsa peatlands show differences in their stable carbon isotope depth profiles indicating enhanced degradation rates. We conclude that the degradation of palsa peatlands by accelerated permafrost thawing can be identified with stable carbon isotope depth profiles. At intact hummocks δ13C depth patterns display the uplifting of peat material by a change in peat decomposition processes.

Palsa Uplift Identified by Stable Isotope Depth Profiles and Relation of δ15 N to C/N Ratio

“…The age of turning points in the present study, based on peat accumulation rates determined by Alewell et al (), is between 80 and 508 years at Stordalen (mean 242 years) and between 243 and 545 years at Storflaket (mean 365 years) (Table ). The younger ages at Stordalen accord with the results in Alewell et al () and Krüger et al () based on stable carbon isotope depth profiles in combination with peat accumulation rates. At Stordalen, palsa initiation was dated to between 120 and 800 years before present (Malmer and Wallén, ; Kokfelt et al, ; Rydberg et al, ), which is within the range of our calculations for palsa uplift.…”

“…The change from fen to bog due to permafrost aggradation was evident in macrofossil and isotopic measurements (Andersson et al, ). The uplift of peat and a corresponding change from minerotrophic to ombrotrophic conditions is supported by the large C/N ratios in the upper part and low C/N ratios in deeper parts of the peat profiles (Krüger et al, ). In some other peat cores from Stordalen the same C/N patterns were found, with a marked change in the C/N ratio from large to small values at a certain depth, and were interpreted as a change from minerotrophic to ombrotrophic conditions (Kokfelt et al, ; Rydberg et al, ).…”

“…Peat C/N ratios cover a wide range. Larger values are found in the upper part of the profiles and smaller values in deeper parts (Krüger et al, ). Greater C/N ratios typify peatlands or peat sequences that accumulate during ombrotrophic conditions, whereas smaller C/N ratios are common for minerotrophic conditions (Andersson et al, ).…”

Rapid organic matter assay of organic matter degradation across depth gradients within marine sediments

“…Although many methods currently exist to measure organic matter degradation in other environments, ROMA is the only method that is applicable to estuarine and marine systems, cost effective and easily adaptable, and allows the user to assess a complete system or size-based community (micro-, meio-, macro-) organic matter degradation ( Sources: *This manuscript, 1 (Dauwe et al, 1999); 2 (Dauwe & Middelburg, 1998); 3 (Vandewiele et al, 2009); 4 (Gestel et al, 2003); 5 (Gongalsky et al, 2008); 6 (Kratz, 1998); 7 (Birchenough et al, 2012); 8 (Kristensen & Blackburn, 1987); 9 (Nickell et al, 2003); 10 (Eggins, 1989); 11 (Jørgensen & Parkes, 2010); 12 (Wellsbury, Herbert, & John Parkes, 1996); 13 (Lillebø et al, 1999); 14 (Tiegs et al, 2007); 15 (Archer & Devol, 1992); 16 (Hargrave & Phillips, 1981); 17 (Coates, Woodward, Allen, Philp, & Lovley, 1997); 18 (Lehmann et al, 2002); 19 (Krüger et al, 2014); 20 (Meyer et al, 2015); 21…”

“…Notable exceptions include stable isotope tracers and amino acid degradation state indices. These methods rely on the use of marked compounds to trace the direct response of a whole community and determine preferential decay rates of different organic compounds (Dauwe & Middelburg, 1998;Dauwe, Middelburg, Herman, & Heip, 1999;Krüger, Leifeld, & Alewell, 2014;Lehmann, Bernasconi, Barbieri, & McKenzie, 2002;Vandewiele, Cowie, Soetaert, & Middelburg, 2009). These methods provide detailed information on organic matter transformation.…”