Effects of small-scale, shading-induced seagrass loss on blue carbon storage: Implications for management of degraded seagrass ecosystems [dataset]

1. Seagrass meadows are important global ‘blue carbon’ sinks. Despite a 30% loss of seagrasses globally during the last century, there is limited empirical research investigating the effects of disturbance and loss of seagrass on blue carbon stocks.
2. In this study, we hypothesised that seagrass loss would reduce blue carbon stocks. Using shading cloth, we simulated small-scale die-offs of two subtropical seagrass species, Halodule wrightii and Thalassia testudinum, in a dynamic northern Gulf of Mexico lagoon. The change in quantity and quality of sediment organic matter and organic carbon were compared among kill, control and bare plots before the kill treatment, shortly after the kill treatment and 11 months after the kill treatment. 210 Pb age dating was performed on bare and Thalassia plots at 11 months to evaluate the impact of sediment erosion in the absence of vegetation.
3. The small-scale die-off led to a 50-65% organic matter (OM) loss in the sediment in the top 8 cm of Halodule plots. Thalassia plots lost significant portions OM (50%) and organic carbon (C; 21-47%) in only the top 1 cm of sediment. The 210 Pb profiles indicated Thalassia die-off reduced the C sequestration rate by 10%, in addition to a loss of ~1 years’ worth of C stocks (~22 g m-2) Furthermore, analyses on O Morg quality indicated a loss of labile OM/C and enhanced remineralisation by microbes.
4. Synthesis and applications: This study provides empirical evidence that small-scale shading-induced seagrass die-offs can reduce seagrass carbon sequestration capacity and trigger losses of blue carbon stocks. While the losses recorded here are modest, these losses in blue carbon storage capacity are notable due to the proximity of shading structures (for example, boat docks) to seagrass habitats. Thus, policies to avoid or protect seagrass habitats from common small-scale, shading disturbances are important for optimising both carbon sequestration capacity and coastline development and management.17-Nov-2017

1. 海草床是全球重要的蓝碳（blue carbon）汇。尽管过去一个世纪全球海草资源流失了30%，但针对海草受干扰及消失对蓝碳储量影响的实证研究仍较为匮乏。
2. 本研究提出假说：海草消失会降低蓝碳储量。研究人员在墨西哥湾北部的动态潟湖中，利用遮光布模拟了两种亚热带海草物种——赖特喜盐草（Halodule wrightii）和海龟草（Thalassia testudinum）的小规模枯萎死亡事件。分别在遮光处理前、遮光处理后不久以及遮光处理11个月后，对比了枯萎组、对照组与裸地组的沉积物有机质与有机碳的含量与质量变化。在处理11个月后，对裸地组和海龟草样地开展铅210（210Pb）测年，以评估无植被覆盖时的沉积物侵蚀影响。
3. 小规模枯萎事件导致赖特喜盐草样地0~8cm层沉积物的有机质（OM）流失50%~65%。海龟草样地仅在表层1cm沉积物中就出现了显著的有机质流失（50%）与有机碳（C）流失（21%~47%）。铅210剖面数据显示，海龟草枯萎不仅造成了约1年的碳储量损失（约22 g·m⁻²），还将碳固存速率降低了10%。此外，对沉积物有机质质量的分析表明，易分解有机质/碳发生流失，且微生物的再矿化作用增强。
4. 综合与应用：本研究通过实证数据证实，小规模遮光诱导的海草枯萎事件会削弱海草的碳固存能力，并引发蓝碳储量损失。尽管本研究记录的损失幅度较为温和，但由于遮光设施（例如船坞）常紧邻海草生境，这类蓝碳存储能力的损失仍不容忽视。因此，出台政策避免或保护海草生境免受常见的小规模遮光干扰，对于优化碳固存能力以及海岸线开发与管理均具有重要意义。2017年11月17日