Department of Ecology, Environment and Plant Sciences, Stockholm University, Stockholm, Sweden; School of Natural Sciences, Technology and Environmental Studies, Södertörn University, Huddinge, Sweden.
Department of Ecology, Environment and Plant Sciences, Stockholm University, Stockholm, Sweden; Institute of Marine Sciences (IMS), University of Dar es Salaam, Zanzibar, Tanzania.
Mar Environ Res. 2022 Apr;176:105608. doi: 10.1016/j.marenvres.2022.105608. Epub 2022 Mar 19.
Seagrass meadows store significant carbon stocks at a global scale, but land-use change and other anthropogenic activities can alter the natural process of organic carbon (C) accumulation. Here, we assessed the carbon accumulation history of two seagrass meadows in Zanzibar (Tanzania) that have experienced different degrees of disturbance. The meadow at Stone Town has been highly exposed to urban development during the 20th century, while the Mbweni meadow is located in an area with relatively low impacts but historical clearing of adjacent mangroves. The results showed that the two sites had similar sedimentary C accumulation rates (22-25 g m yr) since the 1940s, while during the last two decades (∼1998 until 2018) they exhibited 24-30% higher accumulation of C, which was linked to shifts in C sources. The increase in the δC isotopic signature of sedimentary C (towards a higher seagrass contribution) at the Stone Town site since 1998 points to improved seagrass meadow conditions and C accumulation capacity of the meadow after the relocation of a major sewage outlet in the mid-1990s. In contrast, the decrease in the δC signatures of sedimentary C in the Mbweni meadow since the early 2010s was likely linked to increased C run-off of mangrove/terrestrial material following mangrove deforestation. This study exemplifies two different pathways by which land-based human activities can alter the carbon storage capacity of seagrass meadows (i.e. sewage waste management and mangrove deforestation) and showcases opportunities for management of vegetated coastal C sinks.
海草草甸在全球范围内储存着大量的碳储量，但土地利用变化和其他人为活动会改变有机碳（C）积累的自然过程。在这里，我们评估了坦桑尼亚桑给巴尔的两个经历不同程度干扰的海草草甸的碳积累历史。石头城的草甸在 20 世纪经历了高度的城市发展暴露，而 Mbweni 草甸位于一个受影响较小但历史上有清理相邻红树林的地区。结果表明，自 20 世纪 40 年代以来，两个地点的沉积碳积累率（22-25 g m yr）相似，而在过去二十年（约 1998 年至 2018 年），它们的碳积累增加了 24-30%，这与碳源的变化有关。自 1998 年以来，石头城沉积物中碳的 δC 同位素特征（朝着更高的海草贡献方向）增加，表明自 20 世纪 90 年代中期主要污水出口重新安置以来，海草草甸状况得到改善，草甸的碳积累能力得到提高。相比之下，自 21 世纪初以来，Mbweni 草甸沉积物中碳的 δC 特征下降，可能与红树林砍伐后红树林/陆地物质的 C 流失增加有关。本研究例证了两种不同的途径，即陆地人类活动可以改变海草草甸的碳储存能力（即污水废物管理和红树林砍伐），并展示了管理植被沿海碳汇的机会。
