Studies on the diversity of aquatic plants in Lake Xiliang

The diversity of aquatic plants and its changes in Lake Xiliang were studied. Both the mechanisms for the diversity loss and approaches to protect the diversity were also discussed. The main results are given as follows: (1)Seventy seven species distributed in Lake Xiliang in 2001,of which Potamogeton maackianus,Vallisneria denseserrulata,Hydrilla verticillata,P. crispus,Trapa incisa,T. bispinosa,Ceratophyllum demersum,Eichhornia crassipes and Zizania latifolia were dominant species. (2)The vegetation could be divided into 13 communities. In 2001 its coverage was about 61%,and its mean biomass in the whole lake was 1 470.5 g/m 2.(3)The community “ Eichhornia crassipes+Trapa incisa+T. bispinosa Ass”displayed the highest species diversity indices(D=0.849 9,H=2.975 8). Community“ Zizania latifolia-Eichhornia crassipes Ass”and“ Trapa incisa+T. bispinosa Ass” displayed the second highest indices(D=0.840 1,H=2.823 5;D=0.832 4,H=2.888). (4)During the last 20 years a heavy loss in aquatic plant diversity occurred in the lake: the vegetation coverage and biomass decreased by 38.80% and 77.87%,respectively. At the same time 8 aquatic plant species and 4 plant communities disappeared from the lake. (5)It could be concluded that it was violent human disturbance,such as over aquatics breed,over harvest of water grass,dragging for mussels and spiral shells,that led the diversity loss in the lake.