As an existing single species growth model, the logistic model, cannot characterize the population dynamics of algae under hydrodynamic forces. This study is aimed to improve the logistic model under hydrodynamic conditions by examining the responses of cyanobacterium and coupling turbulence mixing and growth of a green algae,Scenedesmus quadricauda,to the population dynamic model. The growth of S. quadricauda under different hydraulic shear force was studied by indoor incubation experiments (25 ℃) with a light intensity of 4,000 lx and light-to-dark ratio of 12 h:12 h. The results showed that all shear and mixing conditions (100, 200, 300 and 400 r∕min) can promote the growth of S. quadricauda a compared to the control condition and all turbulent conditions achieved their peak Chla concentration. While the growth processes of S. quadricauda are approximately the same under different turbulence conditions,which was well fitted by the logistic growth model. Based on the current logistic model and mass transfer theory, a population dynamic growth model (R2> 0.95) of S.quadricauda was developed,which takes into consideration of the impact of hydraulic conditions using the beaker experiment results. The model results indicated that the hydraulic shear force affects maximum algae biomass. In 2 L beaker with limited space,S.quadricauda get the maximum biomass(Chla concentration) of 15,328.2 μg∕L under the average flow rate of 0.101 m∕s,which were 1. 75 times larger than controlled still beakers, which was in agreement with the experiment results. The maximum-biomass promotion coefficient (kM) by mass transfer coefficient (Pe ) was 945. 1. The underlying mechanism can be that the hydraulic shear force timely transports the nutrients timely to algae cell surface, and then increase the algae growth. The hydraulic shear force can change the environment around the laminar layer outside the cell and further affect the algae biomass. The results confirmed the synergistic effect between nutrients transport and hydraulic shear force on the population growth of S. quadricauda.%为了改进现有反映单种群增长的Logistic(逻辑斯特)模型,使其能更好地对水动力影响下藻类的种群动态关系进行表征,进而验证水力剪切作用引起的营养盐混合和均化作用对藻类生长的影响,采用恒温(25 ℃)和恒定光照 (4000 lx,光暗比12 h:12 h)的培养试验,对水华中常见四尾栅藻(Scenedesmus quadricanda)在水力剪切条件下的种群动态增长进行了研究.结果表明:①相对于静止条件,不同的水力剪切(100、200、300和400 r∕min)作用均促进了四尾栅藻的增长,并且均存在最大Chla浓度.②结合藻类种群动态增长的Logistic模型和传质理论,构建了水力剪切效应下单藻种的种群动态增长模型(R2>0.95).模型结果显示,水力剪切作用是藻类最大生物量的控制因素.在空间有限的富营养条件下,Chla浓度在体积平均流速为0.101 m∕s (200 r∕min)条件下的最大生物量为15328.2 μg∕L,是静止条件的1.75倍,大于其他水力剪切条件,与试验结果吻合,传质系数(kc)对四尾栅藻最大生物量的促进系数(kM)为945.1. ③水力剪切主要通过改变藻细胞层流边界层以外环境的营养物质浓度分布,从而对藻类的种群规模产生影响.④水力剪切效应存在边际效应递减的现象,随着剪切强度的增加,在不产生藻类的机械损伤的范围内,藻类种群会达到一个稳定期.研究显示,理论上解释了水力剪切效应对四尾栅藻动态增长的影响机制,实现了水力剪切作用和营养盐通量共同影响四尾栅藻种群增长关系的统一.
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