The attenuation of current‐ and wave‐driven flow within submerged multispecific vegetative canopies
The attenuation of current‐ and wave‐driven flow within submerged multispecific vegetative canopies
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水下多特异性植物冠层内电流和波浪驱动流的衰减
DOI：
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发表时间：
2015
期刊：
影响因子：
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通讯作者：
J. Koseff
中科院分区：
文献类型：
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作者：
Joel S. Weitzman;R. B. Zeller;F. I. Thomas;J. Koseff
从历史上看，淹没的植被树冠要么被报道为单一物种的例子，要么被模仿为单一的例子--仅由单一的植被物种或元素类型组成的群落。对佛罗里达州海湾浅海草甸的实地调查突出了更多样化的底栖生物景观。虽然以地中海藻为主，但群落明显是多物种的，由植物和藻类物种的混合物组成。带状海草元素限定了这些树冠的上部(上层)，而宽体藻类物种则集中在河床(下层)附近。为了预测这种双层树冠结构的水动力影响，我们推导了一个新的树冠流量衰减模型，该模型可以解释垂直树冠的非均质性，就像我们在现场看到的那样。该模型通过一系列实验室实验得到了验证：在水流波浪水槽中安装了多个特定树冠的模拟模型，并暴露在一系列单向和振荡流动中。测量每个树冠上方和内部的平均和脉动速度，以确定植被引起的径流衰减。通过添加林下元素，床层附近的速度显著降低，这一结果与模型预测一致。这些发现表明，对泥沙输送和繁殖体传播等水流调节过程的准确预测依赖于对群落组成的全面计算。这些特性预计也会随着季节变化和间歇性环境压力而发生变化。
Historically, submerged vegetative canopies have either been reported as or modeled after unispecific examples—communities comprised of only a single vegetative species or element type. Field surveys of a shallow Florida Bay seagrass meadow highlighted a more diverse benthic landscape. Although dominated by Thalassia testudinum, the communities were distinctly multispecific, composed of a mixture of both plant and algal species. Strap‐like seagrass elements defined the upper portion of these canopies (the upperstory) while broad‐bodied algal species were found concentrated close to the bed (the understory). To predict the hydrodynamic implications of this dual‐story canopy structure, we derived a new canopy flow attenuation model, formulated to account for vertical canopy heterogeneities like those seen at our field site. The model was validated through a series of laboratory experiments: multispecific canopy mimics were installed in a current‐wave flume and exposed to a range of unidirectional and oscillatory flows. Mean and fluctuating velocity was measured above and within each canopy to determine vegetation‐induced flow attenuation. Velocities near the bed were markedly reduced through the addition of understory elements, results that were consistent with model predictions. These findings suggest that accurate prediction of flow‐regulated processes like sediment transport and propagule dissemination depends on a thorough accounting of community composition. These properties are also expected to change in response to seasonal variability and episodic environmental stresses.