Mapping the degree of decomposition and thaw remobilization potential of soil organic matter in discontinuous permafrost terrain

Abstract

[1] Soil organic matter (SOM) stored in permafrost terrain is a key component in the global carbon cycle, but its composition and lability are largely unknown. We characterize and assess the degree of decomposition of SOM at nine sites representing major land-cover and soil types (including peat deposits) in an area of discontinuous permafrost in the European Russian Arctic. We analyze the elemental and stable isotopic composition of bulk SOM, and the degree of humification and elemental composition of humic acids (HA). The degree of decomposition is low in the O-horizons of mineral soils and peat deposits. In the permafrost free non-peatland soils there is enrichment of 13 C and 15 N, and decrease in bulk C/N ratios indicating more decomposed material with depth. Spectral characterization of HA indicates low humification in O-horizons and peat deposits, but increase in humification in the deeper soil horizons of non-peatland soils, and in mineral horizons underlying peat deposits. GIS based maps indicate that less decomposed OM characteristic of the O-horizon and permafrost peat deposits constitute the bulk of landscape SOM (>70% of landscape soil C). We conclude, however, that permafrost has not been the key environmental factor controlling the current degree of decomposition of SOM in this landscape due to relatively recent permafrost aggradation. In this century, active layer deepening will mainly affect SOM with a relatively high degree of decomposition in deeper mineral soil horizons. Additionally, thawing permafrost in peat plateaus may cause rapid remobilization of less decomposed SOM through thermokarst expansion.Citation: Hugelius, G., J. Routh, P. Kuhry, and P. Crill (2012), Mapping the degree of decomposition and thaw remobilization potential of soil organic matter in discontinuous permafrost terrain,

Multi-proxy study of soil organic matter dynamics in permafrost peat deposits reveal vulnerability to climate change in the European Russian Arctic

“…by Hugelius et al (2012). The DBD sharply increases at the peat/mineral contact in both profiles (Figs.…”

“…1), we have previously characterized decomposition of bulk SOC at the landscape level (Hugelius et al, 2012). In this study, we describe molecular characteristics of SOC stored in the peat plateaus.…”

“…These peat plateaus store the largest amount of SOC in the area (≈65% of all landscape carbon), and are particularly vulnerable to remobilization through thermokarst formation (Hugelius and Kuhry, 2009;Hugelius et al, 2011Hugelius et al, , 2012. The area is currently experiencing permafrost warming and thaw (Oberman, 2008) and, hence, it is of great interest for assessing climate change impacts.…”

“…Gross peat stratigraphy was described in the field. The peat soils were classified as Folic Fibric Cryosols (IUSS Working Group WRB, 2007;Hugelius et al, 2012). In the upper seasonally thawed-out sections, samples were cut out at 1-5 cm (SE8) or 10 cm (SE9) intervals.…”

“…Lignin phenols were isolated from humic acid fractions (Swift, 1996) that were previously isolated using the IHSS method (Hugelius et al, 2012). The alkaline CuO oxidation method was used to extract lignin by mixing < 200 mg sample with 330 mg of CuO in stainless steel Monel reaction vessels (Filley et al, 2008).…”