Fe-C organomineral associations in mangrove soils under a replanting scenario: effects on C stocks and soil quality

Abstract

Mangroves and other coastal wetlands (e.g., seagrass and salt marshes) constitute the so-called Blue Carbon environments, a term referring to the potential of these ecosystems in the sequestration and storage of C, mainly in their soils. In this sense, initiatives that encourage the protection and recovery of mangroves are considered key elements in the fight against climate change. However, despite the recognition of the potential for C storage in mangrove soils, information on the mechanisms of stabilization of organic matter that can contribute to its accumulation remains scarce. Likewise, tools that help in the evaluation of the geochemical functioning and soil quality of mangroves to perform their functions are still limited. This approach is fundamental for the development of strategies and initiatives for the protection and recovery of mangroves in the context of Natural Climate Solutions (NCS), applied in different scenarios. Therefore, the present work aims to evaluate effects of iron oxyhydroxides on organic matter stabilization according to their content and crystallinity degree in order to understand its role in the establishment of soil C stocks in mangroves under different scenarios. Besides, our aim is to test a tool for soil quality assessment using physical, biological and chemical parameters that best express the geochemical functioning of mangrove soils. In this sense, the study will be developed from a 13-year-old mangrove replanting area located in the Northeast region of Brazil and compared with adjacent mature and degraded mangroves. Soil collection campaigns will be carried out in 3, 7, 9 and 13 years of replanting areas, characterizing a chronosequence, besides areas of mature and degraded mangroves. Analyzes of soil physical fractionation, chemical fractionation of the colloidal organic matter, carbon contents, soil density, , sequential extraction of iron, in addition to analyzes for physicochemical characterization (measures of Eh, Ph) are going to be carried out to evaluate the mechanisms of stabilization of organic matter. In addition, the soil quality assessment will be tested using the Soil Management Assessment Framework, a widely recognized soil quality index analysis and production tool that uses physical parameters (e.g., soil density), chemical (content of available nutrients, pH) and biological (content of organic C, characterizations of the microbiota). It is also intended to measure the carbon stock over time associated with the development of organic matter stabilization mechanisms in these soils. The results of this study will serve as a basis for initiatives and projects aimed at the conservation/restoration of this ecosystem as a strategy to face the global climate crisis from the development of low carbon policies based on the concept of NCS.