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A very hot debate is currently focused on submerged substrates that can be classified either as sediments or subaqueous soils. In this paper, the controversy is contextualized on a specific case study, i.e. the Sacca di Goro coastal lagoon facing the North Adriatic Sea. The submerged substrate has been sampled along a a E-W transect and subsequently analyzed to investigate the C-N elemental and isotopic compositions. The recorded concentration of organic carbon (OC) and nitrogen is 0.26-0.50 and 0.02-0.06 wt%, respectively, and the spatial distribution of these parameters highlights a general decrease of concentration from W to E. The carbon isotopic composition of the organic matter (δ13COC) indicates the incorporation within the substrate of significant amount of seaweed and seagrass. Seaweed prevails in the west (δ13COC down to -19‰) due to a nutrient-rich freshwater inflow (Po di Volano), whereas seagrass is preponderant eastward (δ13COC up to -10‰) in a sector of the lagoon fed by riverine waters characterized by lower nutrient load (Po di Goro). The existence of these biological components plausibly implies a lush benthic vegetation, properly rooted on the submerged floor. For this reason, in our view the substrate of the investigated lagoon can be regarded as a subaqueous soil.

Subaqueous soils have to be studied with proper methodologies, according to a pedological approach and considering the key role of animal bioturbation. Morphological and chemical characteristics of submerged soils found in the MPA of "Torre del Cerrano", Adriatic sea (Italy), have been studied in this way, and we conclude that submarine soils of the MPA are important examples of pedogenesis promoted by animals. Soils from the highly protected marine area hosted a major biodiversity than those from the sub- and non-protected areas, while no striking differences in terms of soil physical and chemical characteristics among protected, sub-protected and non-protected areas occurred.

The introduction of the “subaqueous soils” into the international classification system of the Soil Taxonomy (2010) gives a possibility to soil scientists to use the pedogenetic approach to investigate coastal soils in view of resource protection and valorization. Coastal areas, in fact, are complex and fragile ecosystems whose ecological value is worldwide recognized, but generally highly inhabited and affected by different erosion and pollution phenomena, and flooding problems. The soil science has a great opportunity to contribute to the correct management and protection of coastal soils, by recognizing the value of coastal soils and thus investigating the effect of the water table oscillation and ionic composition to the changes of soil properties and functionality. This work represent a first attempt to describe the soil continuum existing from hydromorphic to subaqueous environment, highlighting the evidence of some pedogenetic processes into subaquatic substrates and demonstrating the high ecological values of these pedons.