Effects of nonlocal turbulence on the mass transfer of dissolved species to reef corals
Effects of nonlocal turbulence on the mass transfer of dissolved species to reef corals
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DOI：
10.4319/lo.2007.52.1.0274
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发表时间：
2007-01-01
影响因子：
4.5
通讯作者：
Koseff, Jeffrey R.
中科院分区：
文献类型：
--
作者：
Falter, James L.;Atkinson, Marlin J.;Koseff, Jeffrey R.
我们研究了非局部湍流对于圆柱体和珊瑚礁模型中溶解物种的质量转移的重要性。固体石膏圆柱体和石膏涂层模型珊瑚以4.5 和10 cm s(-1) 的平均流速溶解在室外水槽中。使用了三种模型珊瑚：鹿角珊瑚属和波西洛波拉属的两种分枝珊瑚，以及扁脑属的一种叶状珊瑚。湍流强度 (Tu) 被测量为随时间变化的流动的标准偏差与平均值的比率。 5% 到 55% 之间的 Tu 是通过两个垂直喷射阵列泵送水而独立于平均流量而产生的。在考虑两种平均流速的情况下，所有形式的传质系数随湍流强度增加 10-70% (p < 0.05)；然而，分枝珊瑚的传质系数对湍流强度的变化不像叶状珊瑚那样敏感。圆柱体的结果与工程文献一致，并表明当分支尺寸或流速（或两者）变得非常小时，湍流强度对传质的影响变得更弱。在实验珊瑚群落周围和自然存在的珊瑚礁群落上方测得的湍流强度通常在 15% 到 35% 之间变化。假设平均湍流强度约为 25%，则完全忽略非局部湍流的影响将导致叶状珊瑚形式的传质系数最多 +/- 10% 和分支珊瑚形式最多 +/- 5% 的不确定性。对于大多数底栖珊瑚礁系统生物地球化学速率的评估来说，测量总体流中的外部湍流并不是必需的。
We examined the importance of nonlocal turbulence to the mass transfer of dissolved species from both cylinders and models of reef coral. Solid gypsum cylinders and gypsum-coated model coral were dissolved in an outdoor flume at mean flow speeds of 4.5 and 10 cm s(-1). Three model corals were used: two branched forms of the genera Acropora and Pocillopora, and one lobate form of the genus Platygyra. Turbulence intensities (Tu) were measured as the ratio of the standard deviation of the time-variant flow to the mean. Tu of between 5% and 55% were created independently of the mean flow by pumping water through two vertical arrays of jets. Mass transfer coefficients increased by 10-70% with turbulence intensity for all forms at both mean flow speeds considered (p < 0.05); however, mass transfer coefficients for the branched coral were not as sensitive to changes in turbulence intensity as for the lobate coral. Results for the cylinders were consistent with the engineering literature and indicate that the effects of turbulence intensity on mass transfer become weaker when branch size or flow speed (or both) become very small. Turbulence intensities measured around experimental coral communities and above naturally occurring reef communities typically vary between 15% and 35%. Assuming an average turbulence intensity of around 25%, then ignoring the effects of nonlocal turbulence altogether would result in uncertainties in mass transfer coefficients of at most +/- 10% for the lobate coral form and +/- 5% for the branched coral forms. Measuring external turbulence in bulk flows is not necessary for most evaluations of biogeochemical rates in benthic reef systems.