Subaqueous soils and preliminary considerations on the occasional formation of “fairy circles” in the Comacchio saline (Province of Ferrara, Italy)

Abstract

The results of a survey carried out inside the salt basins of the Comacchio Saline (Province of Ferrara, Italy) are reported, occasionally affected by the formation of numerous submerged circular shapes of approximately two meters in diameter and whose crowns quickly tend to darken. A rare phenomenon that has so far only been reported in China in the Shanghai swamps, which have been called "fairy circles". The coordination of pedological and microbiological investigations on soils that are permanently submerged (Typic Sulfiwassents) or occasionally emerged (Aeric Sulfiwassents) has highlighted how the formation of the "fairy circles" of the Comacchio salt pans can be attributed to concomitant exogenous conditions (increase in temperatures and salinity of water) and endogenous (gas emissions of methane and sulfur dioxide), which is followed by intense bacterial activity and proliferation of microalgae which explain the darkening of the crowns. It was also possible to highlight a different distribution of bacteria along the profiles with dominance of methanogens in the epipedon and of sulfur reducers below it.

Keywords

• fairy circles
• hydromorphic and subaqueous soils
• methanogenic bacteria
• sulphite and sulphate reducing bacteria