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Abstract
Mangrove wetlands of the Niger Delta are among the largest blue-carbon ecosystems in Africa, yet oil pollution and the spread of the invasive palm Nypa fruticans are changing what they store and how they function. This study examined blue carbon stocks, nutrient dynamics, and ecosystem health across three stand conditions in Rivers and Bayelsa States: intact Rhizophora-dominated mangrove at Buguma Creek, oil-impacted mangrove at Bodo Creek, and Nypa-invaded fringe along the Brass, St Nicholas River. Twelve 10 m × 10 m plots (four per condition) were sampled in the dry and wet seasons of 2025. Vegetation structure, pore-water chemistry, and sediment cores to 100 cm were analyzed for bulk density, organic carbon, total nitrogen, and total phosphorus. Ecosystem carbon was estimated from sediment and biomass pools, and a composite health index was computed from canopy, regeneration, native dominance, dissolved oxygen, and bare ground. Intact stands stored 812 ± 64 Mg C ha⁻¹, oil-impacted stands 446 ± 51 Mg C ha⁻¹, and Nypa stands 304 ± 38 Mg C ha⁻¹. Sediment held 80, 88% of the stock. One-way ANOVA showed a significant condition effect on sediment carbon, F(2, 9) = 82.7, p < .001. Oil-impacted plots had elevated ammonium and total nitrogen, depressed dissolved oxygen, and poor seedling recruitment. Nypa plots were nutrient-poorer and structurally simplified. Sediment organic carbon was strongly correlated with the health index (r = .86, p < .001). The study concludes that degradation is already a carbon and nutrient problem, and that protecting remaining Rhizophora stands is the highest- return action for both ecosystem health and climate mitigation.