Fine‐scale field measurement of benthic flow environments inhabited by stream invertebrates
Fine‐scale field measurement of benthic flow environments inhabited by stream invertebrates
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河流无脊椎动物栖息的底栖流动环境的精细尺度现场测量
DOI：
10.4319/lo.1996.41.2.0297
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发表时间：
1996
影响因子：
4.5
通讯作者：
A. Jasentuliyana
中科院分区：
文献类型：
--
作者：
D. Hart;B. Clark;A. Jasentuliyana
我们使用热膜风速仪来量化悬浮摄食的幼虫黑蝇(Simulium Vittatum)栖息的石头表面附近细微尺度的流动的空间和时间变化。我们特别关注了幼虫斑块状微分布和水流速度局部空间差异之间的协变模式。电流速度以256赫兹采样，高度在床上1至10 mm之间。流速剖面形状复杂，边界层厚度为5 mm。在床面上方2 mm处测得的平均流速(幼虫摄食附属物的大致高度)在7到59厘米之间，S-‘。目前在床上10毫米处测量的速度对于在2毫米高度测量的速度预测非常差。幼虫的丰度与2毫米高度的水流速度呈显著正相关，并解释了石头内速度的变化-59%的丰度变化。流速时间序列表现出明显的细尺度时间非均质性，波动幅度可达80 cm S-L，最大加速度有时超过1×10~4 cm S~(-*)，这表明倾向于将底栖生物逐出床面的力可能大于以前基于恒定流假设的估计值。观测到的湍流程度比传统的边界层理论预测的要大。我们认为，在个别石头上明显的大部分湍流不是由局部剪切产生的，而是继承自导致流动分离的上游粗糙度元素。
We used hot-film anemometry to quantify fine-scale spatial and temporal flow variations near the surfaces of stones inhabited by suspension-feeding larval blackflies (Simulium vittatum). We focused especially on within-stone patterns of covariation between patchy microdistributions of larvae and local spatial variations in current speed. Current speeds were sampled at 256 Hz for heights between 1 and 10 mm above the bed. Profiles of current speed exhibited complex shapes, and boundary-layer thicknesses ranged from 5 mm. Average current speeds measured 2 mm above the bed (the approximate height of larval feeding appendages) ranged between 7 and 59 cm s- ‘. Current speeds measured 10 mm above the bed were very poor predictors of speeds measured at the 2-mm height. Larval abundance exhibited a significant positive relationship to current speed at 2-mm height, and within-stone variations in speed explained -59% of the variation in abundance. Time series of current speed exhibited marked fine-scale temporal heterogeneity, fluctuating by as much as 80 cm s-l in ~0.1 s. Maximum accelerations sometimes exceeded 1 x lo4 cm s-*, which suggests that the forces tending to dislodge benthic organisms from the bed may be greater than previous estimates based on assumptions of steady flow. Observed levels of turbulence were greater than predicted from traditional boundary-layer theory. We suggest that much of the turbulence evident on individual stones is not produced by local shear but is inherited from upstream roughness elements that cause flow separation.