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不同水力剪切效应下四尾栅藻的种群动态增长模型研究
李飞鹏1, 刘燕如1, 陈瑞弘2, 张海平3
1.上海理工大学环境与建筑学院;2.丹华水利环境技术(上海)有限公司;3.同济大学环境科学与工程学院
摘要:
为了改进现有反映单种群增长的逻辑斯特(Logistic)模型以便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,对水华中常见绿藻四尾栅藻(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,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Chl-a浓度。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,①水力剪切作用是藻类最大生物容量的控制因素。在空间有限的富营养条件下,Chl-a浓度在体积平均流速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2.2倍,大于其他水力剪切条件,与试验结果吻合,传质系数Pe对四尾栅藻最大生物量的促进系数kM为945.1。②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。③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。本研究从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。
关键词:  水力剪切  四尾栅藻  种群动态  模型
DOI:
分类号:
基金项目:国家自然科学基金项目(51409190,51379146)
Population Dynamic Growth Model of Scenedesmus quadricanda under Different Hydraulic Shear force
Li Feipeng,et al
Abstract:
The existing single species growth model, Logistic model, does not characterize the population dynamics of algae under hydrodynamic forces. This study aims 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 quadricaudain, to the population dynamic model. The growth of Scenedesmus quadricauda under different hydraulic shear force was studied by indoor incubation experiments (25 oC) with a light intensity of 4000 lx and light-to- dark ratio of 12:12. The results show that all shear and mixing conditions (100, 200, 300 and 400 r/min) can promote the growth of Scenedesmus quadricauda compared to the control condition and all turbulent conditions achieved their peak Chl-a concentration. While the growth processes of Scenedesmus quadricauda are approximately the same under different turbulence conditions, which was in agreement with the logistic growth model. Based on the current logistic model and mass transfer theory, a population dynamic growth model (R2 > 0.95) of Scenedesmus quadricanda 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 2L beaker with limited space, Scenedesmus quadricanda get the maximum biomass (Chl-a concentration) of 15328.2 μg/L under the average flow rate of 0.101m/s, which were 2.2 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 Scenedesmus quadricanda.
Key words:  hydraulic shear force  Scenedesmusquadricauda  population dynamic  model