Chemical and pedological features of subaqueous and hydromorphic soils along a hydrosequence within a coastal system (San Vitale Park, Northern Italy)

Transitional systems are complex and fragile ecosystems where the water table oscillation plays a fundamental role in soil and landscape development. Due to global climate change, by the end of the next century a large part of these environments will be affected by water flooding, causing deep changes to soil properties and functionality. Increasing the knowledge on the genesis and properties of these soils can be fundamental for providing useful tools for the correct management of this natural resource. The transition from wetland to hydromorphic interdune system in the coastal area of the S. Vitale park (Northern Italy) represents a unique soil hydrosequence characterized by soils which undergo continuous or partial, permanent or periodic saturation and reduction. These hydrosequences offer a great opportunity to investigate how soil properties change in the transition from subaqueous to hydromorphic soils and to understand which pedogenetic processes mostly characterize the soil development under different water saturation conditions. In this study, the soil transition through the hydrosequence was recognized by the evaluation of some morphological (e.g. Munsell color) and chemical (organic carbon, sulfur ratio, CaCO3 content) soil properties that could trace the extent of sulfidization and decarbonation processes along the soil sequences. The presence of salts of marine origin characterized the subaqueous pedons, while nutrients accumulation (i.e., phosphorous) increased with soil emersion. These hydrosequences represent a soil continuum where the duration of water saturation and the oscillation of the water table along the soil profiles strongly affect some specific soil-forming processes that involve S redox transformation, P accumulation, CaCO3 depletion and salt accumulation.