Time since deglaciation and geomorphological disturbances determine the patterns of geochemical, mineralogical and microbial successions in an Icelandic foreland

Abstract

Glacier forelands are an ideal natural laboratory to study the initial stages of pedogenesis. Here, we document a build-up in organic carbon (C), nitrogen (N) and phosphorous (P), an increase in bacterial communities as well as a progression of physical and chemical weathering along a ~2 km long and 122 yr old chronosequence in the glacier foreland of Fláajökull in south-eastern Iceland. We complemented this chronosequence dataset with an assessment of the variability in soils that were affected by geomorphological disturbances along a 175-m long toposequence transect. While soils at the crest of the toposequence moraines were anomalously under-developed due to frequent erosion, the soils at the footslopes were characterized by a more advanced successional stage in that they benefited from an ample supply of nutrients, fine and more weathered materials as well as higher moisture. The large variability in soil properties across the toposequence demonstrates that, even across short distances, disturbances driven by hillslope and glacio-fluvial processes can lead to substantial heterogeneities in soil development in glacier forelands. We emphasize that the geochemical and biological features of soil development and patterns of succession in glacier forelands should be interpreted as the result of both changes in time since deglaciation and geomorphological disturbances.