[Succession Pattern of Phytoplankton of Daning River in the Three Gorges Reservoir and Its Driving Factors].

To elucidate succession pattern of phytoplankton in the Daning River and its driving factors, multivariate statistical analysis was conducted. By using the monitoring data in different seasons of Daning river during April 2012 to January 2013, this paper analyzed the succession pattern of phytoplankton in the Daning River and its driving factors in typical tributaries of river-style reservoirs. According to the characteristics of water level, the operational period of the TGR was classified into following four stages:stage Ⅰ (pre-November-April), stage Ⅱ (May-July), stage Ⅲ (July-September) and stage Ⅳ (September-November). ① The results indicated that the values of Chlorophyll-a concentrations and algal density showed similar seasonal variations, with the highest values occurring in stage Ⅲ, followed by stages Ⅳ, Ⅱ and Ⅰ. Succession of C-R-S growth strategies was the same generally:CR-R type dominated in stage Ⅰ, CS, CR/CS and R-CR dominated in stage Ⅱ, Ⅲ and Ⅳ, respectively. ② The mean values of Margalef index and Pielou index in stage Ⅳ and Ⅲ were significantly greater than those in stage Ⅱ and Ⅰ; the value of Shannon-waver index showed that the highest value in stage Ⅲ, followed in a descending order by stage Ⅰ,Ⅱ and Ⅳ; the successional rate had the highest value in stage Ⅳ, followed in descending order by stage Ⅲ, Ⅰ and Ⅱ. ③ The results of Correlation analysis suggested that no significant relationships were observed between the environmental parameters and phytoplankton abundance in stage Ⅰ. The results indicated that relative water column stability(RWCS), index of feasible energy for phytoplankton (Et) and index of feasible energy (Ef*) were key regulatory factors for phytoplankton community in stage Ⅰ. The results indicated that Et, Ef* and total phosphorus (TP) were key regulatory factors for phytoplankton abundance in stage Ⅱ. The results of the redundancy analysis (RDA) suggested that RWCS, TP and the ratio of euphotic depth[Deu(λPAR)] to mixing depth (Dmix)[Deu(λPAR)/Dmix] were key regulatory factors for phytoplankton community composition in stage Ⅱ. The results indicated that Ef* and TP were key regulatory factors for phytoplankton abundance in stage Ⅲ. The results of the RDA suggested that[Deu(λPAR)/Dmix],Et, Ef* and TP were key regulatory factors for phytoplankton community composition in stage Ⅲ. The results indicated that TP was key regulatory factor for phytoplankton abundance in stage Ⅳ. The results of the RDA suggested that[Deu(λPAR)/Dmix] was key regulatory factor for phytoplankton community composition in stage Ⅳ.

[Influence of Periodic Temperature Disturbance on the Succession of Algal Community Structure].

In order to study the mechanism of the habitat disturbance of reservoir on algae blooms, some interior control experiments about the feature of algal diversity and the succession of community structure under different temperature disturbance cycle but the same amplitude condition were conducted, based on the intermediate disturbance hypothesis and combined with algal community habitat selection theory and ecological functional groups of algae. The results showed that:① the intermediate disturbance would accelerate the growth of algae and increase their diversity. Under the gradient of the intermediate disturbance group Δ22℃/48h, the diversity of phytoplankton was the highest, and the biomass reached the maximum, however, without absolute dominant algal species. While in the high frequency disturbance group Δ22℃/24h the biodiversity was relatively lower, but the algae biomass was reduced. ② the periodical change of temperature had obvious influence on the succession of the phytoplankton community, and the dominant species also presented certain differences. The succession of the algal advantageous function group followed the basic rule of X1(Chlorella)→J(Scenedesmus)→S1(Phormidium) or X2 (Chlamydomonas), and the community structure also presented a trend that the C/CR type algae took advantage and the superiority was gradually replaced by R type algae. When the high temperature disturbance was frequent, the R type algae (S1) was distinctly ascendant. During the experiment, the community structure was given priority to the C/R strategy algae with no or low disturbance. However, the coexistence of algae with different growth strategies was evident in group Δ22℃/48h. Meanwhile, the S strategy algae (L0) resistant to high temperature stress began to emerge.