Preliminary study on algae composition of a river entering Taihu Lake and effect of constructed wetland on algae removal

Abstract

In order to study the effect of vertical flow constructed wetland (VFCW) on algae removal in the period of algae bloom in Taihu Lake, VFCW was constructed at the riparian area of Xiaoxia River, a river entering Taihu Lake. The algae compositions of water from Xiaoxia River, influent and effluent of VFCW were analyzed and the effect of VFCW on algae removal was studied on different days. The results show that the density and biomass of algae at different sampling sites on different days were quite different, and there was no obvious proportional relationship between the cell density and biomass of algae at the same sampling site at the same sampling time. There are 6 phyla of algae in all the samples, involving 92 species, among which the dominant species are Chlorophyta (35 species), while the least species are Pyrrophyta (2 species). The cell density was dominated by Cyanophyta, and the species were mainly Planktolyngbya subtilis, Microcystis sp., Merismopedia minima. Three sampling tests were conducted on different days in one month, and the results showed that the overall algae removal rates of VFCW on these three days were 70.1 %, 90.2 % and 99.9 % respectively. The average removal rates of different phyla were all above 82.0 %. The algal density and biomass of VFCW effluent were far lower than those of other sampling sites, indicating that VFCW had a good efficiency of algae removal when treating algae-laden water from Xiaoxia River of west island (also called Taihu Ecological Island).