Abstract: A field survey was conducted on the species composition, community type, distribution pattern, and biomass of aquatic vegetations in the Baiyangdian Lake of Hebei Province. A total of 39 species were observed, including 16 emergent species, 14 submerged species, 6 floatingleaved species, and 3 floating species, belonging to 21 families and 32 genera. Compared with those about 15 years ago, 9 species were disappeared, community types were decreased from 16 to 13, and some predominant communities with large distribution area, such as Hydrilla verticillata and Najas major, were not found in the present survey. Meanwhile, the distribution pattern of aquatic vegetations was greatly changed. The biomass of aquatic vegetations decreased dramatically, compared to the survey in 1980. Human cultivation, random discharge of pollutants, and tremendous change of water level could be the main reasons for the degradation of aquatic vegetations and the great change of their distribution pattern in the Lake.

Key words: straw carbon source, microbial biomass carbon, microbial biomass nitrogen, protozoa abundance, relative abundance.