Genesis of hydromorphic Calcisols in wetlands of the northeast Yucatan Peninsula, Mexico

Tropical wetlands are fragile ecosystems controlled by hydrological factors. They are less studied than wetlands of the temperate and subtropical areas, and limited information is available about soil genesis in such systems. Here, we present a soil study of a wetland in the Yalahau region of the northeastern Yucatan Peninsula, in order to assess the properties and understand the genesis of these hydromorphic soils. An east–west transect was established through the wetland to understand differences in soil processes between shallower deposits at the edge of the wetland and thicker deposits at the center of the wetland. Contrary to the central image of peaty and gleyic wetland soils, the dominant soil unit in the wetland examined in the current study is a Calcisol. According to their properties we assume that the Bk horizons of these soils are the product of neoformation, as they consist principally of micritic groundmass. Shells of terrestrial mollusks are also present, and constitute the coarser fractions. The micrite in these soils is proposed to have been synthesized through participation of algae when periodic flooding with waters from karstic geosystems, rich in dissolved carbonates (from limestone dissolution), affects the area. Algae develop intensely on the surface of the flood water, forming periphyton. The algae consume CO2 dissolved in water through photosynthesis, thus displacing the bicarbonate (soluble)–carbonate (low solubility) equilibrium in favor of carbonate formation. Profiles near the edge of the open wetland show a carbonate-enriched horizon (Bk) overlaying the organic matter-enriched horizon (Ah). We conclude that alternation of horizons enriched with organic material and carbonates reflects the duration of floods: more prolonged flooding promotes algae productivity and carbonate precipitation, while organic matter accumulation is inhibited.