Spatial And Temporal Distribution Characteristics Of Phytoplankton Functional Groups And Their Responses To Eutrophication In Two Deep Reservoirs,southwest China

In order to explore the distribution characteristics of phytoplankton functional groups and their responses to eutrophication in Wanfeng Reservoir and Longtan Reservoir,phytoplankton and water samples were taken in dry period(January 2015), level period(April 2015) and wet period(July 2015).There existed 34 genera and 7 phyla phytoplankton in Wanfeng Reservoir, and 32 genera and 6 phyla phytoplankton in Longtan Reservoir. Green algae had the largest number of species and the largest density, followed by diatom. Both reservoirs owned the dominant species(genus) of Scenedesmus bijuba, Chlorella sp. and Cyclotella sp. in different seasons. The cell density of phytoplankton was the highest in wet period, followed in level period and dry period.17 phytoplankton functional groups were identified in Wanfeng reservoir with the dominant functional groups of J, X1, B, P, D, Xph, G and T. Longtan reservoir owned 15 phytoplankton functional groups with the dominant functional groups of J, X1, B, P, G, MP, Lo and T. The similarity of functional groupsbetween two reservoirs reached 88.2%, indicating that their water environment was similar.Dominant functional groups had obvious distribution patterns and phytoplankton growth strategy: Wanfeng reservoir, J/B/P in the dry period, X1/J/Xph in the level period and J in the wet period, CR/R in dry periodâ†'CR/C in level periodâ†'CR in wet period; Longtan reservoir, J in the dry period, X1/J/B in the level period and J/P/G/X1/Lo in the wet period, CR in dry periodâ†'CR/C in level periodâ†'C/CR/S/R/CS in wet period. Longtan reservoir owned the S/CS strategy more than Wanfeng reservoir, indicated more perfect seasonal succession process.The vertical distribution of J/X1/B reflected little difference in Wanfeng reservoir, as the same as Xph/G/T. Cordon P occupied the predominant position on surface layers, and Cordon Lo was predominant in little layers. Cordon J was absolute dominant functional group in dry period of Longtan reservoir. X1 occupied the predominant position in the sampling point of Xiaomachang, Hongshuihezhen and Shuangjiangkou during level period, while X1, J and B became the first dominant functional groups on different layers in Dam. X1, J became the first dominant functional group on different layers in Xiaomachang, Hongshuihezhen and Shuangjiangkou, and J occupied the predominant position in Dam.On the dry period and common period, the water were mesotrophy in two reservoirs. On the wet period, the middle layers and bottom layers were in mesotrophic state, surface layers were eutrophy lightly, and the water was grossly mesotrophy in Longtan reservoir, middle eutrophy appears only once in the wet period, but the water was at the top of the mesotrophy mostly. Compared with previous studies, there were little difference with Wanfeng reservoir, but the nutrition level of Longtan reservoir have increased.Multivariate analysis(RDA) indicated WT and transparency were the main factors affecting the spatial and temporal distribution of dominant functional groups rather than nutrients in Wanfeng reservoir. But from Pierce correlation analysis, the abundance of functional groups was positively correlated with NO3-N, and negatively correlated with NO2-N, PO4-P. So, nutrients were still an indispensable factor on growth and reproduction of phytoplankton. Compared to Wanfeng reservoir, WT, TN, PO4-P, NO3-N, NO2-N, SD were the main factors in Longtan reservoir.Judging from the dominant functional groups, the two reservoirs showed mesotrophy bias in eutrophy, this was incompatible from the judgment of comprehensive nutritive index, but correspondent to the judgment of TN nutritive index. Due to high concentration of nitrogen nutrient levels, much of phytoplankton indicating eutrophication occupied the predominant position in mesotrophic reservoir.