Windsock behavior: climatic control on iron biogeochemistry in tropical mangroves

Abstract

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 lmol g -1 ; dry season: 230 lmol 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,

Applying the Soil Management Assessment Framework (SMAF) to Assess Mangrove Soil Quality

“…Given the importance of anaerobic metabolism in the diverse soil functions of mangrove soils [84][85][86], future studies should consider other biological indicators in the minimum dataset, such as microbial biomass carbon and the enzymatic activity of β-glucosidase, both of which already have scoring curves in the algorithms within the SMAF spreadsheet. Additionally, other chemical indicators (e.g., the Fe and S content) may play a key role in predicting soil functions because the quantity of these elements directly affects important soil processes within mangrove soils (e.g., pyritization) [51,87]. These indicators are not available in the current version of the SMAF spreadsheet; therefore, developing reliable scoring curves for new indicators such as these is a challenging task for future soil quality research in mangrove soils.…”

Recovery of Soil Processes in Replanted Mangroves: Implications for Soil Functions

“…Solid-phase Fe partitioning was performed to assess the recovery of soil processes associated with Fe and S dynamics in the studied mangrove soils [48,49]. This method has been largely used in mangrove soil studies [14,17,39,50] and allows the obtainment of six distinct, operationally defined Fe fractions:…”

“…After total O 2 consumption by aerobic respiration, facultative and obligate anaerobic microorganisms progressively use oxidized species (NO 3 − , Mn 4+ , Fe 3+ , SO 4 2− , CO 2 , and N 2 ) as electron acceptors for soil organic matter decomposition [11,12]. In mangrove soils, microbial-mediated reductions of Fe 3+ and SO 4 2− are the main metabolic pathways for soil organic matter decomposition [13,14]. These anaerobic pathways contribute to low decomposition rates and, consequently, to a high accumulation of organic matter in mangrove soils, recognized as natural carbon sinks [12,15].…”

“…These anaerobic pathways contribute to low decomposition rates and, consequently, to a high accumulation of organic matter in mangrove soils, recognized as natural carbon sinks [12,15]. Additionally, the Fe 3+ and SO 4 2− metabolic pathways release Fe 2+ and sulfides, which may precipitate as pyrite, mackinawite, and acid-volatile sulfides [14,16]. These sulfides represent one of the most stable sinks for potentially toxic elements [17,18].…”

“…In this sense, organic matter accumulation and pollutant immobilization are two key services directly controlled by the soils of mangrove forests through their unique soil biogeochemical processes [14,19,20]. In recent decades, the recognition of mangrove forests' relevance has stimulated the restoration of initiatives worldwide, which occurs mainly through seedling plantation [21][22][23].…”