Effects Of Several Ecological Factors On The Growth, Photosynthesis And Chlorophyll Fluorescence Of Some Algae From Wujiang River

Since 1980s 'water bloom' has been frequently observed in Wujiang river, especially in spring and autumn. When the Three Gorges project is finished in 2009, water level rise of the reservoir will go upstream in Wujiang river to Wulong, consequently, the flow velocity of Wujiang river from Wulong to Fuling (the confluence of Wujiang with Yangtze river) decreases. This flow velocity change leads to profound alteration in hydrology and hydraulics of Wujiang river from Wulong to Fuling. Due to this flow velocity change, the deposition of the suspended substances is enhanced and light environment of the water body may be improved. Furthermore, because of this decreased flow velocity, more time will be taken by water body travels from Wulong to Fuling and as a result more time algae will have to grow before they go into Yangtze river. All these factors may increase the possibility of occurrence of 'water bloom' in Wulong-Fuling section of Wujiang river. In order to explore the effects of Three Gorges dam construction on algae growth in Wujiang river and give prediction for probable water bloom, we conducted some experiments and want to know the impact of some ecological factors including light, temperature and flow velocity on algae's growth and photosynthesis.In the experiment, Chlorella pyrenoidosa, Nitzschia sp., Synechocystis aquetilis and algae in Wujiang river were selected as our experimental materials. We investigated the effects of light, temperature and flow velocity on the growth, photosynthesis and chlorophyll fluorescence characters of the algae, and got the following results.(1) We investigated the effects of temperature alteration on light energy utilization and growth of Chlorella pyrenoidosa Chick, growing under different light intensity conditions, and aimed to ascertain whether the influence of light intensity on light energy utilization and growth of phytoplankton is affected by temperature. Our research clearly demonstrated that temperature elevation enhanced the dissipation of absorbed light energy as heat of C. pyrenoidosa exposed to high light intensity conditions, and therefore reduced the positive effects of light intensity augmentation on the growth of C. pyrenoidosa. The optimal light levels for growth of C. pyrenoidosa was lowered at higher temperature due to the suppression effect of temperature elevation on light energy utilization and growth.For either light intensity or temperature, the increment of light or temperature within appropriate range is beneficial to the growth of C. pyrenoidosa. However, the optimality of light intensity is changed due to the alteration in temperature. Therefore, when we consider whether the temperature or light intensity is optimal for the growth of algae, the interaction of these two variables needs to be taken into account.(2) In order to determine whether there is a significant linear relationship between electron transport rate (ETR) and oxygen evolution under variable temperatures, Chlorella pyrenoidosa, Nitzschia sp. and Synechocystis aquetilis were selected as experimental algae and their growth, photosynthesis and electron transport rate were analyzed. We investigated the effect of temperature on the ratio of gross photosynthesis (Gross P) to electron transport rate (ETR) of these three species of algae. The results showed that the ratio of Gross P/ ETR increased significantly with temperature decrease for all three species. The results revealed that there is a non-linear relationship between ETR and oxygen evolution, which demonstrated that ETR measurements can not be used to accurately estimate oxygen evolution under variable temperatures.(3) In order to understand the effect of flow velocity change on the algae growth and competition in Wujiang river, four different seasons characteristic of different light and temperture environments were simulated and the growth of algae from Wujiang river affected by these simulated seasons were analyzed. It is found that chl-a concentration was higher in flowing cultures than in quiescent ones. In simulated summer, the proportion of cyanobacteria among all cyanobacteria, green algae and diatom cultivated quiescently is significantly higher than that in the flowing cultures. In simulated spring & autumn, the proportion of green algae cultivated quiescently is significantly higher than that in flowing cultures. However, the proportion of diatom cultivated in flowing conditions is significantly higher than that in quiescent culture at simulated spring, autumn and summer. It is shown in the results that, in simulated winter, diatom proportion is significantly higher than the other two algae: cynobacteria and green algae. This implies that diatom have relatively higher growth in winter, which may lead to resultant high concentration of diatom in the next coming spring.