Holocene environmental change and development of the nutrient budget of histosols in North Iceland

Abstract

Little is known about vegetation changes in Icelandic peatlands in the context of soil chemical properties. By connecting soil chemical and physical characteristics with palaeobotanical data we examined interactions between climate, histosols, vegetation and land use during the Holocene. Exchangeable base cations, cation exchange capacity (CEC), base saturation (BS), decomposition rates, using carbon:nitrogen ratio (C:N) and von Post humification, and soil physical properties were determined. Vegetation development was reconstructed based on pollen analysis. The impact of geographic location was examined by comparing results from three sloping fens (coastal, inland and highland fringe). Minerogenic content was highest in the proximity of the active volcanic zone, reflected in higher C:N and nutrient content in the histosol profiles of the fens inland and at the highland fringe. The coastal site revealed exceptionally high BS. C:N was either stable throughout the profile or increased with depth. Plant species richness, and evenness based on pollen data, and pollen concentrations were greatest at the site with lowest nutrient levels. Minerogenic content facilitates the ability of histosols to bind nutrients. Plant growth is optimised at the sites with lower fertility levels. C:N alone is not a reliable indicator of decomposition rates, but depends on the quality of the organic parent material. Environmental conditions driven by climate changes caused alterations in vegetation and soil properties before the human settlement of Iceland (c. AD 870), but overall the histosols showed resilience towards severe degradation. After the settlement, the histosols struggled to buffer the impact caused by destruction of vegetation and increased erosion. This study increases our understanding of environmental and anthropogenic determinants of soil- and vegetation development.