The Research On Distribution Characteristics And Biodiversities Of Submerged Macrophytes In Dawangtan Reservoir Catchment

With the increasing of human activities,biodiversities has decreased severely. The decrease of biodiversities has been the important problems which drew more and more global attention. Species diversity is the basis and core of biodiversity protec- tion and research works, which is a part of biodiversities. Insight into the nature of sci -ence and the regularity of change of species diversity as well as their relation to the environmental factors is of great value to the biodiversity protection. The article takes the Dawangtan Reservoir Catchment of Nanning,Guangxi as the study area. Take the investigation and sampling of distribution,community and variety of submerged mac- rophytes in this area as well as their habitats'humane and natural conditions and then analyze the distribution characteristics and biodiversities of submerged macroph- ytes in Dawangtan Reservoir Catchment as well as their living environment,growth factor in Mar.and Dec.of 2009.The investigation shows that:(1)The 6 kinds of submerged macrophytes gathered from Dawangtan reservoir catchment in 2009 belong to 4 species,3 families. they are all aquatic vascular plants,among which,2 kinds belong to Hydrocharitaceae 3 kinds belong to Potamo -getonaceae 1 kind belong to Ceratophyllaceae(2)Hydrilla verticillata and Ceratophyllum demerswn L are the main species in upper waters of Dawangtan reservoir catchment,while the main species in lower rea ches of Bachijiang river is Vallisneria natans.Dawangtan reservoir catchment belongs to artificial dam area,there is no distribution of submerged macrophytes.There are no whole watershed species.Vallisneria natans,Hydrilla verticillata,Potamogeton crispus can distribute all over the drainage area of the Dawangtan reservoir.What's more, distribution frequency of Vallisneria natans is 100% in lower reaches of Bachijiang river .Ceratophyllum demersum L.,Potamogeton maackianus A. Benn,Zannichellia -ceae can be found in the upper waters of Dawangtan reservoir. As to distribution ki - nds, there are 3 kinds in lower reaches and 6 kinds in upper waters drainage area of Dawangtan reservoir. Submerged macrophytes which have the highest distribution frequency in research area are Vallisneria natans, then Potamogeton crispus, Hydrilla verticillata and Ceratophyllum demersum L. The distribution frequency of Zanniche -llia L. and Potamogeton maackianus is the same and also the lowerest. Vallisneria natans has the largest biomass per unit area and highest degree of dominance.(3) there are 12 communities in 32 sampling points of Submerged Macrophy -tes in Dawangtan Reservoir Catchment, which are communities of Vallisneria natans, Hydrilla verticillata, Vallisneria natans+ Hydrilla verticillata, Vallisneria natans +Pota -mogeton crispus, Hydrilla verticillata+ Ceratophyllum demersum L., Ceratophyllum demersum L.+ Potamogeton crispus, Vallisneria natans+ Potamogeton maackianus , Vallisneria natans+ Ceratophyllum demersum L.+ Potamogeton crispus,Vallisneria natans+ Zannichellia L.+ Potamogeton crispus, Hydrilla verticillata+ Zannichellia L., Ceratophyllum demersum L.+ Potamogeton maackianus+ Potamogeton crispus, Potamogeton maackianus+ Zannichellia L.+ Potamogeton crispus etc.Scatter points of multiple community are dispersive,and the number is also little. The scope of most multiple communities is also very little. While singular communities which let Vallis- nerianatans dominates have been the majority of the submerged macrophytes in the whole catchment area. So on the whole, submerged macrophytes communities in Dawangtan reservoir catchment are very simplex, diversity of community is also not higher.(4) The results of multiply analysis of Braun-Blanquet rank division showed that the ranks of submerged macrophytes in Dawangtan reservoir catchment were low with the abundance index of 2.62, which showed that species diversity of submerged macrophytes in Dawangtan reservoir catchment is very low. Kinds and biomass of submerged macrophytes is also very low. Compared with other district in Guangxi, submerged macrophytes'Simpson diversity index and Shannon-wiener information index are both very low in Dawangtan reservoir catchment.(5)The research shows that the influencing determinants of submerged macrophytes in the study area are depth of water, substrate, season, water velocity, human activities and water PH value. According to the influencing degree to the growth and distribution and diversity of submerged macrophytes, these influencing determinants can be divided into two parts, the main influencing determinants are depth of water, substrate, season, water velocity, while human activities and PH value have minor influence.From the results of the submerged macrophytes species diversities in Dawang- tan reservoir catchment, submerged macrophytes communities was mainly composied of single plant. The species diversities or community diversities were relatively low. It showed strong impact of environment existed in this area. Through the research work, we get the first-hand materials of field trip and collection, and get rudimentary grasp of distribution characteristics and diversity of submerged macrophytes in Dawangtan reservoir catchment, which has some meanings to research on the submerged macro- phytes and the environmental monitoring in this area in the future.