Abstract:

Taxonomic composition, distribution and cell densities of phytoplankton community of Niyang River were investigated in August 2009.The phytoplankton was mainly composed of diatom,204 taxa belong to 24 genus (including variations) were observed.Relative abundances of most taxa were low,dominant species were not outstanding,the taxa of mean relative abundance more than 5% were 〖WTBX〗Achnanthes minutissima〖WTBZ〗 (90％),〖WTBX〗Ceratoneis arcus〖WTBZ〗 var.〖WTBX〗linearis〖WTBZ〗 (54％),〖WTBX〗Fragilaria intermedia〖WTBZ〗 (53％) and 〖WTBX〗Synedra acus〖WTBZ〗 (50％);their appearance frequencies were 19,20,17 and 20,respectively.Distribution of taxa is even,the mean density of phytoplankton was 225×104 ind./L during the studying period,this value was far below the general rivers and lakes.ShannonWeaver index of diversity and the evenness index of phytoplankton were very high in most sampling sites,their mean values was 364 and 095,respectively.These structure characteristics indicated that phytoplankton of this valley was a complex,stable community,and trophic state of Niyang River was oligotraphentic.The detrended correspondence analysis (DCA) was consistent with that of twoway indictor species analysis (TWINSPAN),the result of DCA showed that altitude and environmental stabilization were the major factor that affected diversity of phytoplankton community in Niyang River