THE EFFECTS OF A NEW CERAMSITE ECOLOGICAL FLOATING BED ON THE WATER QUALITY AND PHYTOPLANKTON IN GRASS CRAP CULTURE PONDS

In order to study the effects of a new ceramsite ecological floating bed on the phytoplankton community in fishponds, we conducted continuous and regular surveys on the phytoplankton community and the water quality indexes in six grass crap culture ponds from May to October in 2013. Ceramsite ecological floating beds were applied in three ponds as the test groups and the other three were the control groups. During the culture period, we identified 179 species that belonged to 8 phyla and 111 genera. Ninety-three species were Chlorophyta, 25 were Cyanophyta, 23 were Bacillariophyta, 17 were Euglenophyta, 6 were Xanthophyta, 5 were Dinophyta, 5 were Cryptophyta and 5 were Chrysophyta. In the presence of the new ceramsite ecological floating bed, the test groups exhibited higher water transparency and lower concentrations of major nutritive salts compared to the control, and there was little fluctuation in the physical-chemical indexes during the culture. There was a remarkable difference in the planktonic algae community between the test and the control groups in the middle and later culture period. In the mean while, the number of species in the test groups was higher than that in the control groups. There was a insignificant difference in the quantity of phytoplankton between the test and the control groups of which the ranges were 101.95106614.95106 ind./L and 151.43106612.60106 ind./L respectively. The ranges of biomass were 90.79402.85 mg/L and 116.33831.55 mg/L respectively, which were significantly different between the two groups in the middle and later culture period. The contribution of Chlorophyta and Cyanophyta was over 90%. The structure of phytoplankton community showed an obvious seasonal variation: the density and biomass of Chlorophyta first increased and then decreased, while those of Cyanophyta had an opposite trend. In the beginning, Scenedesmus was the dominant species in all ponds; a month later, Merismopedia and Microcystis were dominant in the control and Scenedesmus in the test groups; Merismopedia was the dominant species in July and August and then Scenedesmus and Chlorococcum became dominant. There was an insignificant difference between the test and the control groups in terms of the diversity index, and the ranges of species richness, Shannon-Weiner Index and Simpson's diversity index were 3.165.59, 1.502.46 and 0.540.87 respectively. Ecological Floating Bed may help improve the water quality, enrich the algae species components, and reduce the risks of overly high biomass and harmful algae blooms.