Pedogenic Processes in a Posidonia oceanica Mat

Scientists studying seagrasses typically refer to their substratum as sediment, but recently researchers have begun to refer to it as a soil. However, the logistics of sampling underwater substrata and the fragility of these ecosystems challenge their study using pedological methods. Previous studies have reported geochemical processes within the rhizosphere that are compatible with pedogenesis. Seagrass substratum accumulated over the Recent Holocene and can reach several meters in thickness, but studies about deeper layers are scarce. This study is a first attempt to find sound evidence of vertical structuring in Posidonia oceanica deposits to serve as a basis for more detailed pedological studies. A principal component analysis on X-Ray Fluorescence-elemental composition, carbonate content and organic matter content data along a 475 cm core was able to identify four main physico-chemical signals: humification, accumulation of carbonates, texture and organic matter depletion. The results revealed a highly structured deposit undergoing pedogenetical processes characteristic of soils rather than a mere accumulation of sediments. Further research is required to properly describe the substratum underneath seagrass meadows, decide between the sediment or soil nature for seagrass substrata, and for the eventual inclusion of seagrass substrata in soil classifications and the mapping of seagrass soil resourcesThis work has been funded by project SUMILEN (CTM2013- 47728-R, MINECO). C. Leiva-Dueñas was supported by a PhD scholarship funded by the Spanish Ministry of Science and Innovation (FPU15/01934); O. Serrano was supported by an ARC DECRA DE170101524. Authors would like to thank the use of RIAIDT-USC analytical facilities. This is a paper from the Group of Benthic Ecology 2014 SGR 120S