Tracking mangrove restoration using a biogeochemical soil health index and ecosystem service indicators

Mangrove forests provide critical soil-related ecosystem services (ES), including carbon sequestration, contaminant retention, and nutrient cycling-all closely linked to soil health. However, land-use change and pollution increasingly threaten mangrove soils, compromising their functionality and ES provision. To reverse these impacts, effective strategies must begin with robust assessments of soil health using key indicators that also reflect ecosystem functions. Despite their importance, soil health indexing methods for mangroves remain underdeveloped. This study proposes a soil health index (SHI) for mangrove ecosystems, applied in northeastern Brazil across degraded, restoring (9 and 13 years), and mature forests. We assessed variables linked to biogeochemical processes governing carbon dynamics (soil texture, soil organic carbon - SOC, pseudo-total Fe), contaminant immobilization (exchangeable, carbonate-bound, oxyhydroxide-bound, and pyritic Fe, redox potential, and pH), and nutrient cycling (β-glucosidase, acid phosphatase, and available phosphorus). SHI was constructed using a minimal dataset selected via principal component analysis. Mature mangroves showed the highest SHI values (0.99 ± 0.03), while degraded sites had the lowest (0.25 ± 0.01). Replanted areas displayed intermediate SHI values (0.37 ± 0.01 at 9 years; 0.52 ± 0.02 at 13 years), indicating gradual recovery. ES provision estimates followed the same trend. The SHI effectively captured soil health changes across degradation and restoration gradients and is a promising tool to inform decision-makers, support conservation planning, and communicate complex data in accessible formats. This approach strengthens links between science, restoration action, and ecosystem service outcomes.