Seagrass meadows are important carbon sinks in the global coastal carbon cycle yet are also among the most rapidly declining marine habitats. Their ability to sequester carbon depends on flow–sediment–vegetation interactions that facilitate net deposition, as well as high rates of primary production. However, the effects of seasonal and episodic variations in seagrass density on net sediment and carbon accumulation have not been well quantified. Understanding these dynamics provides insight into how carbon accumulation in seagrass meadows responds to disturbance events and climate change. Here, we apply a spatially resolved sediment transport model that includes coupling of seagrass effects on flow, waves, and sediment resuspension in a seagrass meadow to quantify seasonal rates of sediment and carbon accumulation in the meadow. Our results show that organic carbon accumulation rates were largely determined by sediment accumulation and that they both changed non-linearly as a function of seagrass shoot density. While seagrass meadows effectively trapped sediment at meadow edges during spring–summer growth seasons, during winter senescence low-density meadows (< 160 shoots m⁻²) were erosional with rates sensitive to density. Small variations in winter densities resulted in large changes in annual sediment and carbon accumulation in the meadow; meadow-scale (hundreds of square meters) summer seagrass dieback due to marine heatwaves can result in annual erosion and carbon loss. Our findings highlight the strong temporal and spatial variability in sediment accumulation within seagrass meadows and the implications for annual sediment carbon burial rates and the resilience of seagrass carbon stocks under future climate change.

中文翻译：

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海草的季节性生长和衰老改变了沿海泻湖的沉积物积累速率和碳埋藏

海草草甸是全球沿海碳循环中重要的碳汇，但也是衰退最快的海洋栖息地之一。它们隔离碳的能力取决于促进净沉积的流动-沉积物-植被相互作用，以及初级生产力的高速度。然而，海草密度的季节性和周期性变化对净沉积物和碳积累的影响尚未得到很好的量化。了解这些动态有助于深入了解海草草地中的碳积累如何响应干扰事件和气候变化。在这里，我们应用了一个空间分辨的沉积物迁移模型，该模型包括海草对海草草甸中流动、波浪和沉积物再悬浮的影响的耦合，以量化草甸中沉积物和碳积累的季节性速率。我们的研究结果表明，有机碳积累率很大程度上取决于沉积物的积累，并且它们都随着海草枝条密度的变化而非线性变化。虽然海草草甸在春夏季生长季节有效地捕获草甸边缘的沉积物，但在冬季衰老期间，低密度草甸（< 160 芽 m^-2 ) 是侵蚀性的，速率对密度敏感。冬季密度的微小变化导致草地年沉积物和碳积累的巨大变化；由于海洋热浪，草甸规模（数百平方米）的夏季海草枯死会导致年度侵蚀和碳损失。我们的研究结果强调了海草草甸内沉积物积累的强烈时空变异性，以及对未来气候变化下年沉积物碳埋藏率和海草碳储量恢复力的影响。