The influence of sediment mobility and channel geomorphology on periphyton abundance
The influence of sediment mobility and channel geomorphology on periphyton abundance
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DOI：
10.1111/fwb.12865
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发表时间：
2017-02-01
影响因子：
2.7
通讯作者：
Brown, Logan
中科院分区：
文献类型：
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作者：
Hoyle, Joanna T.;Kilroy, Cathy;Brown, Logan
河流管理者目前很难预测水流状况和营养物质变化对附着生物生物量的综合影响。生物量的积累被认为是通过增加养分、光照和温度来促进的，而生物量的损失则与无脊椎动物的放牧和水文扰动有关。然而，在一系列河流中可靠的生物量预测因子已被证明是难以捉摸的。一个可能的原因是，在预测模型中使用的干扰阈值通常与流量指标，而附着生物去除机制（当前的阻力，磨损和摩尔行动的移动的沉积物）更直接地涉及到水力和地貌条件。我们探讨了这种可能性，通过相关的附着生物去除事件的水力阈值泥沙夹带在18砾石卵石床河流到达附着生物覆盖和营养盐浓度进行了定期监测。我们将观察到的阈值放电去除附着生物到剪切应力阈值使用水力模型。我们的结果表明：（i）河床物质的较细部分（2- 16 mm）的磨蚀是去除附着生物的主要物理机制;（ii）这种细河床物质的流动频率是附着生物丰度的主要控制因素;（iii）促进生长的变量，如营养物浓度，往往只在沉积物运动频率较低时才对附着生物丰度起重要作用。这些发现突出了站点之间的地貌差异的重要性，并解释了为什么一个单一的流量指标可能是一个穷人的预测地貌不同的河流的附着生物丰度。我们的分析表明，分区网站的沉积物流动性（无论是沙子或D-50）的频率的基础上，可以提高网站的可预测性，有可能发展的滋扰水平的附着生物。
River managers currently have difficulty predicting the combined effects of changes in flow regime and nutrients on periphyton biomass. Biomass accumulation is known to be promoted by increasing nutrients, light and temperature, and its loss has been related to invertebrate grazing and hydrological disturbance. However, biomass predictors that are reliable across a range of rivers have proven elusive. One possible contributing reason is that disturbance thresholds used in predictive models are typically linked to flow metrics, whereas the mechanisms for periphyton removal (current drag, abrasion and molar action by mobile sediment) relate more directly to hydraulic and geomorphic conditions. We explored this possibility by relating periphyton removal events to hydraulic thresholds for sediment entrainment in 18 gravel- to boulder-bed river reaches at which periphyton cover and nutrient concentrations had been regularly monitored. We converted observed threshold discharges for periphyton removal into shear stress thresholds using hydraulic models. Our results demonstrate that: (i) abrasion by finer fractions of the bed material (2-16mm) was the dominant physical mechanism removing periphyton; (ii) the frequency of mobility of this fine bed material was the dominant control on periphyton abundance and (iii) growth-promoting variables, such as nutrient concentrations, tended to only become important to periphyton abundance when the frequency of sediment movement was low. These findings highlight the importance of geomorphic differences between sites and explain why a single flow metric may be a poor predictor of periphyton abundance across geomorphically different rivers. Our analysis suggests that partitioning sites based on frequency of sediment mobility (either sand or the D-50) could improve predictability of sites at which there is potential for nuisance levels of periphyton to develop.