Quantifying carbon stocks in mangrove estuaries of two coastal cities in Tanzania

Mangrove forests offer a wide range of ecosystem services, including coastal protection and climate regulation. These ecosystems serve as significant carbon sinks, effectively sequestering and storing carbon in their biomass and sediments. However, various human activities have an impact on carbon stocks in mangroves. The current study quantifies the carbon stored in mangrove forests of the Mtoni estuary in Dar es Salaam and the Kisiju estuary in Pwani, Tanzania, from 40 random sampling plots. Seven species of mangroves Avicennia marina (Forssk.) Vierh (Acanthaceae), Bruguiera gymnorrhiza (L.) Lam. (Rhizophoraceae), Ceriops tagal (Perr.) C. B. Rob, Heritiera littoralis Dryand. (Malvaceae), Xylocarpus granatum Koen. (Meliaceae), Sonneratia alba J. Smith (Lythraceae), and Rhizophora mucronata Lam were identified. Allometric models were used to estimate aboveground carbon (AGC) and belowground carbon (BGC). An organic elemental analyser determined the organic carbon content in the sediments, followed by calculations using a specific equation for soil organic carbon (SOC) content. Analysis revealed that the mean total carbon stock density in the Mtoni estuary is 334.7 ± 37.88 t/ha, which is equivalent to 1228 t CO₂ ha. In contrast, Kisiju stored 345.6 ± 31.7 t/ha, which is equivalent to 1268 t CO₂ ha. AGC averages 36.81 ± 7.06 t/ha in Mtoni and 70.65 ± 8.83 t/ha in Kisiju, whereas BGC averages 6.52 ± 1.23 t/ha and 16.61 ± 1.71 t/ha, respectively. The SOC density is greater in Mtoni at 291.45 ± 29.59 t/ha than that in Kisiju at 258.45 ± 21.16 t/ha, constituting 82% of the total carbon pool. The capacity of carbon storage in these mangrove ecosystems highlights their role in mitigating climate change. Nonetheless, fluctuations in carbon stores can be attributed to factors such as conservation status, deforestation rates, salinity, sediment deposition, ecosystem productivity, human disturbances, and urban pollution. The findings highlight the need for further conservation measures to enhance carbon storage and address climate change, offering critical information to policymakers.