Convection and diffusion processes of buoyant organisms are of great significance to ecological restoration or the restoration of the riparian and wetland system. Advection–diffusion models have been widely applied to describe the transport of particles through vegetation, assuming that the particle transport is driven by the mean flow, but few studies have been conducted on the diffusion process while considering the retention time. The authors conducted flume experiments of four runs with different vegetative densities and extracted and analysed the longitudinal moving and lateral oscillation trajectories of buoyant particles. The trapping and releasing mechanisms of buoyant particles due to capillary force were explored, and a dimensionless parameter is defined to reflect the effect of the physical properties of stems and particles on the retention time. The retention time of trapping events due to the capillary force between particles and the stem has been proven to follow a three-parameter double exponential distribution, the duration time of both short and long retention events increases with the bulk flow velocity, and the proportion of long trapping events decreases with the increasing bulk flow velocity. The diffusion coefficient of buoyant particles is validated independently from the vegetative densities, increases with the flow velocity, and is approximately 100 times that of the solute in the flow through emergent vegetation under similar condition.

中文翻译：

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浮生颗粒簇在硬质植被明渠流中的扩散特性

浮力生物的对流和扩散过程对于生态恢复或河岸湿地系统的恢复具有重要意义。平流扩散模型已被广泛应用于描述颗粒通过植被的输送，假设颗粒输送是由平均流量驱动的，但在考虑保留时间的情况下对扩散过程进行的研究很少。作者进行了四次不同植物密度的水槽实验，提取并分析了浮力颗粒的纵向移动和横向振荡轨迹。探讨了毛细管力对浮力颗粒的捕获和释放机制，并定义了一个无量纲参数来反映茎和颗粒的物理性质对保留时间的影响。由于颗粒和茎之间的毛细管力而引起的捕获事件的保留时间已被证明遵循三参数双指数分布，短保留事件和长保留事件的持续时间随着总体流速的增加而增加，并且长捕获事件随着总体流速的增加而减少。浮力颗粒的扩散系数独立于植被密度进行验证，随着流速的增加而增加，大约是相似条件下流过挺水植被的溶质扩散系数的 100 倍。