The trend of biodiversity changes of planktonic algae in the reverse succession of macrophyte-type lakes in middle reaches of the Changjiang River

The present paper report the species composition, density and seasonal tendency of diversity indices of planktonic algae in five lakes at different phases of reverse succession. The Biandantang, the South Qinglinghu and Qiaodunhu Lakes belong to macrophyte - type (3.4 - 8.5Kg cntdot m-2) and the Huangjiahu and the North Qinglinghu Lakes belong to algae - type (0.2kg cntdot m-2). 129 common planktonic algae species belonging to 80 genera were collected in Qiaodunhu Lake. In Biandantang Lake and South - Qinglinghu Lake, there were 112 species, 82 genera and 134 species, 84 genera respectively. In Huangjiahu Lake there were 101 species, 68 genera and the North - Qinglinghu Lake 62 species 47 genera. The number of species and genus of planktonic algae reduced with the decrease of biomass of macrophyte. The relationship between species number (SN) of planktonic algae and biomass of macrophyte (B-M, Kg cntdot m-2) can be expressed as following: SN = 100.53 + 3.8556B-M. The dominant species of planktonic algae among different lakes showed different seasonal variations. The dominant species appearing in the Qiadun, Biandantang and the south qinglinghu lakes were 36, 31 and 34 species respectively, and 31 and 28 species respectively in Huangjiahu and the North - Qinglinghu lakes. The simlarity coefficient of Qiaodunhu - Qingling was 0.715; the Qiaodunhu - Biandantang 0.691; Biandantang - the South - Qiuglinghu 0.661. The planktonic algae density was lower in the macrophyte -type lake. In the Qiaodunhu, Biandantang and the south Qinglinghu lakes, the average annual density was 165. 81 times 10-4, 136.49 times 10-4 and 234.52 times 10-4 ind cntdot L-1 respectively. The planktonic algae density is higher in the algae - type take. In the Huangjiahu and the North - Qinglinghu lake, the average annual density was 1856.4 times 10-4 and 3058.8 times 10-4 ind cntdot L-1 respectively. The planktonic algae density rose with the decrease in the macrophyte. The maximum planktonic alage density appeared in spring in Qiaodunhu, in autumn in Qinglinghu, Biandantang and the North Qinglinghu, and in summer in the Huangjiahu. In the Qiaodunhu, Biandantang and the South - Qinglinghu lakes, the average annual diversity indexes of planktonic algae were 3.793, 4.176 and 4.072 and in the Huangjiahu and the North - Qinglinghu lake were 3.279 and 3.004. The relationship among planktonic alage diversity indexes (H') and biomass of macrophyte(B-M, Kg cntdot m-2), conductivity (cond, mu-s cntdot cm-2), inorganic nitrogen(IN, mg cntdot L-1) or total phosphorus (TP, mg cntdot L-1) ran be expressed as following: H' = 3.0984 + 0.6329 (B-M) - 0.0599 (B-M)-2, H' = 5.15 -7.506cond, H' = 4.164 -1.117IN, H' = 4.01 - 5.126TP. The Cyanophyta quotients were 0.97, 4.22 and 1.65 in the Qlaodunhu, Biandantang and the South Qinglinghu lakes respectively. The compound quotient of algae were 1.79, 5.67 and 2.65 respectively; the three lakes belong to Oligotrophic, eutrophic and mesoeutrophic type separately. The Cyanophyta quotients were 5.43 and 12.50 in the Huangjiahu and the North qinglinghu lakes. The compound quotient of algae were 10.0 and 20.50. They belong to saper over eutrophic type. The fuzzy cluster analysis was applied to study the simmilarity of the community structure of planktonic algae in the Qlaodunliu, Biandantang, Huangjiahu, the South and North Qinglinghu lake.