Beach wracks are temporary accumulations of vegetal detritus that can be found along coastlines all over the world. Although beach wracks are often perceived as a nuisance for beach users, they play a crucial ecological role in carbon and nutrient connectivity across ecosystem boundaries, especially when they reach a relevant size, as in the case of the wedge-shaped seagrass accumulations called banquette. In this study, three-dimensional mapping of a giant Posidonia oceanica banquette was carried out for the first time using high-resolution UAV photogrammetry combined with field sampling and compositional and chemical analysis. The combined approach allowed a reliable estimation of the amount and spatial distribution of both vegetal biomass and sedimentary mass, as well as of total carbon, nitrogen and phosphorus content, revealing that i) banquette act as a sediment trap and represent hot spots of seagrass biomass and carbon accumulation; ii) banquette thickness, rather than the distance from the sea, influences the spatial distribution of all variables. Moreover, high-resolution digital elevation models (DEM) revealed discontinuous patterns in detritus accumulation resulting in an unknown banquette type here termed “Multiple Mega-Ridge banquette” (MMR banquette). On the one hand, this study highlighted the high potential of the UAV approach in very accurately 3D mapping and monitoring of these structures, with relevant implications for ecosystem service estimation and coastal zone management. On the other hand, it opened new questions about the role played by temporary beach wracks and, in particular, by P. oceanica banquette in the blue carbon exchange across land-ocean boundaries.

海滩残骸是植物碎屑的临时堆积物，可以在世界各地的海岸线上找到。尽管海滩残骸通常被认为是海滩使用者的麻烦，但它们在跨生态系统边界的碳和养分连通性方面发挥着至关重要的生态作用，特别是当它们达到相关大小时，例如称为楔形海草堆积的情况宴会. 在这项研究中，一个巨人的三维映射Posidonia oceanica 宴会首次使用高分辨率无人机摄影测量结合现场采样以及成分和化学分析进行。联合方法可以可靠地估计植物生物量和沉积质量的数量和空间分布，以及总碳、氮和磷含量，揭示 i)宴会充当沉积物陷阱，代表海草生物量和碳积累的热点；ii)宴会厚度，而不是离海的距离，会影响所有变量的空间分布。此外，高分辨率数字高程模型 (DEM) 揭示了碎屑堆积的不连续模式，导致未知宴会在此处键入称为“多个 Mega-Ridge”宴会”（MMR宴会）。一方面，本研究强调了无人机方法在对这些结构进行非常准确的 3D 测绘和监测方面的巨大潜力，对生态系统服务估计和海岸带管理具有相关意义。另一方面，它提出了关于临时海滩残骸所起的作用的新问题，特别是P. oceanica banquette在陆地-海洋边界的蓝色碳交换中。