Tracing blue carbon flows across diverse seascapes

Abstract: Plants occupying coastal ecosystems draw in carbon dioxide (CO2) from the air and water around them during photosynthesis. A fraction of this CO2 becomes fixed into plant biomass and can eventually contribute to the blue carbon pool—organic carbon (Corg) sequestered in slow-turnover sinks. An important step in protecting and enhancing this natural carbon sequestration pathway is determining the relative contributions of different coastal plants to this blue carbon pool in durable sinks. We compiled a global dataset of coastal soil carbon measurements and used a Bayesian hierarchical meta-regression model to explore the relative contribution of local (autochthonous) versus external (allochthonous) sources of Corg in the soils beneath tidal saltmarsh, mangrove, and seagrass wetlands. We found most soil Corg in coastal wetlands came from allochthonous sources, rather than the habitat-forming plants. Managing climate-resilient blue carbon seascapes, therefore, requires an awareness of this portfolio of contributors to soil carbon sequestration. However, study design aspects such as soil sampling depth, levels of sample replication, and the modelling approach used to trace Corg can have pronounced effects on the estimated contributions of different carbon sources. We outline a roadmap for improving how we track the various drivers of soil carbon sequestration in diverse mosaics of coastal vegetation.

摘要：栖息于海岸生态系统的植物在光合作用过程中，会从大气及周边水体中吸收二氧化碳（CO₂）。其中一部分CO₂会被固定为植物生物量，最终可汇入蓝碳（blue carbon）库——即封存于低周转碳汇中的有机碳（Corg）。保护并强化这一自然固碳途径的关键一环，是明确不同海岸植物对持久碳汇中蓝碳库的相对贡献。我们整合了一套全球海岸土壤碳测量数据集，并采用贝叶斯分层元回归模型（Bayesian hierarchical meta-regression model），探究了潮汐盐沼、红树林与海草湿地土壤中，有机碳的本地生源（autochthonous，原地源）与外源（allochthonous，异地源）两类来源的相对贡献占比。研究发现，海岸湿地土壤中的绝大多数有机碳均来自外源，而非构建该生境的本土植物。因此，若要管理具备气候韧性的蓝碳海域景观，需充分认识到土壤碳固存的贡献来源具有多样性。不过，研究设计的诸多方面——例如土壤采样深度、样本重复水平以及用于示踪有机碳的建模方法——都会对不同碳源的估算贡献量产生显著影响。我们提出了一套优化路线图，用以改进在多样海岸植被镶嵌分布区域中追踪土壤碳固存各类驱动因子的相关工作。