The effects of seaward distance on above and below ground carbon stocks in estuarine mangrove ecosystems

Abstract Background: Mangrove forests have gained recognition for their potential role in climate change mitigation due to carbon sequestration in live trees, and carbon storage in the sediments trapped by mangrove tree roots and pneumatophores. Africa hosts about 19% of the world’s mangroves, yet relatively few studies have examined the carbon stocks of African mangroves. The available studies report considerable differences among sites and amongst the different pools of carbon stocks. None considered the effects of seaward distance. We present details of AGC and SOC carbon stocks for Lindi in Tanzania, and focus on how these values differ with increasing seaward distance and, how our results compare to those reported elsewhere across Africa.Results: AGC ranged between 11-55Mg C ha-1, but was not significantly affected by seaward distance. SOC for 0-1m depth ranged from 154-484, with a mean of 302 Mg C ha-1. SOC was significantly negatively correlated with seaward distance. Mangrove type (estuarine/oceanic), soil erosion, soil depth may explain these differences We note important methodological differences in previous studies on carbon stocks in mangroves in Africa. Conclusion:This study indicates that seaward distance has an important effect on SOC stocks in the Lindi region of Tanzania. SOC should be fully incorporated into national climate change mitigation policies. Studies should report seaward distance and to describe the type of mangrove stand to make results easily comparable across sites and to assess the true value of Blue Carbon in Africa. We recommend focusing on trees >10cm diameter for AGC, and sampling soils to at least 1m depth for SOC, which would provide a more complete assessment of the potentially considerable mangrove carbon store.