Sediment provenance, soil development, and carbon content in fluvial and manmade terraces at Koiliaris River Critical Zone Observatory

Abstract

The purpose of this study was the investigation of sediment provenance and soil formation processes within a Mediterranean watershed (Koiliaris CZO in Greece) with particular emphasis on natural and manmade terraces. Koiliaris CZO is characterised by steep slopes, abrupt climatic changes, complex geology and most importantly by a significant anthropogenic influence. Material and methods Five sites (K1-K5) were excavated and analysed for their pedology (profile description), geochemistry (including Rare Earth Elements and other trace elements), texture and mineralogy along with chronological analysis (optical luminescence dating). The selected sites have the common characteristic of being flat terraces where soil formation has been taking place and erosion is low. The selected sites differed with regard to bedrock lithology, elevation and land use. Soils were classified as, Fluvisol (K1-K2), Leptosol (K3) and Cambisol (K4-K5). Results and discussion Three characteristic processes of soil genesis were identified: i) sediments transportation from outcrops of metamorphic rocks and sedimentation to fluvial sites (K1-K2), ii) in situ soil development in terraces with metamorphic rocks as parent material (K3) and in terraces with limestone as parent material (K4), and iii) strong eolian input and/or material transported through gravity from upslope at the mountainous site (K5). Only two sites revealed pedogenic processes such as a) calcite deposition in the fluvial environment (K1) which was a relict evidence of dry period and b) clay illuviation and REE horizonization at site K4 which corresponded to wetter period in Greece (medieval warm period). The REE patterns revealed strong 58 characteristics inherited from the bedrock at sites K4 and K5, while MREE and HREE depletion were observed at K1, K2 and K3 sites. Carbon sequestration throughout the soil profile was high at manmade terraces at higher elevation compared to fluvial environments due to both climatic effects and possibly intensive anthropogenic impact. Conclusions Soils at Koiliaris CZO are rather new soils with limited evolution. Pedogenic processes were identified in the older sites like K1 site. The manmade terraces at higher elevation have much higher carbon sequestration compared to the anthropogenic impacted fluvial areas. The intense agriculture activities have discernible impact in the upper soil horizon even at higher elevation sites like the site K3.