Windsock behavior: climatic control on iron biogeochemistry in tropical mangroves

Iron is one of the most abundant elements on the planet and a micronutrient for most organisms. In many coastal regions worldwide, mangrove forests affect the dynamics and mobility of different elements to the oceans especially through their soils. The biogeochemistry of mangrove soils responds to numerous factors that vary within different spatial and time scales. In this sense, seasonality can be crucial in determining the role of these ecosystems towards the iron biogeochemical cycle. Thus, the main goal of the present study was to assess the effects of contrasting climatic conditions on iron biogeochemistry in different mangrove forests along the Brazilian coast. We studied the soils (n = 435) of 14 different mangrove forests distributed along two contrasting climate regions: the semi-arid Northeast and the humid Southeast coasts of Brazil. In the SE region, water surplus and lower temperatures in both seasons did not cause significant changes in iron concentrations (wet season: 216 µmol g−1; dry season: 230 µmol g−1) where oxyhydroxides and pyrite immobilize iron in the mangrove soils. In contrast, in the semi-arid mangroves, a marked water deficit during the dry season caused both pyrite oxidation and iron reprecipitation as oxyhydroxides. Contrarily, in the rainy season, the establishment of a suboxic environment (Eh ~  + 100 mV) favored significant iron losses via iron reduction. We conclude that seasonality can affect the maintenance and cycling of iron in mangrove soils, which may function as important sources of this element for adjacent ecosystems.