Andic Soil Properties and Tephra Layers Hamper C Turnover in Icelandic Peatlands

Due to frequent volcanic activity and erosion of dryland soils, magnified by land use after human settlement (ca. 870 CE), peatlands in Iceland receive regular additions of mineral eolian deposits. Their soils may develop not only histic but also andic characteristics. Yet, mineral eolian deposition as an environmental determinant of peatlands in Iceland is still poorly understood, not least with regard to the peatlands carbon (C) stores. This study advances our understanding of the impact of tephra deposition on Histosols by elucidating interactions between C characteristics and andic soil properties. We compare Histosols from three Icelandic peatlands of different degrees of exposure to eolian deposition by evaluating data sets of their C structure derived by C-13 NMR spectroscopy, andic soil properties based on selective extractions of Al, Fe, and Si, and decomposition proxies C/N, delta C-13, and delta N-15. By applying multivariate statistical methods, we are able to present several important patterns. Soil organic matter of Histosols with andic properties is less decomposed than that of Histosols without notable andic properties. Andic soil properties seem to impact their C structure by facilitating the formation of organo-mineral complexes, which particularly hamper the decomposition of chemically more labile C groups. Tephra layers appear to hamper microbial activity in deeper soil layers by preventing input of fresh organic matter. The interaction of andic and histic soil properties and the protective role of major tephra deposits may enable an unusual potential for long-term C stabilization in a natural peatland environment.

Automated summary

This study investigates the impact of tephra deposition on peatlands in Iceland, specifically looking at the interactions between soil carbon characteristics and andic properties. The research shows that Histosols with andic properties have less decomposed organic matter and that andic soil properties facilitate the formation of organo-mineral complexes, which hampers the decomposition of labile carbon groups. Tephra layers appear to inhibit microbial activity in deeper soil layers by preventing the input of fresh organic matter, potentially leading to long-term carbon stabilization in natural peatland environments.