Study On The Optimization Of Submerged Mcrophytes Community Structure In The West Of Hangzhou West Lake

Aquatic plants are the primary producers in water, and submerged maerophytes are the foundation of maintaining creature multiplicity. The instauration of submerged maerophytes is the key of ecological restoration. The environmental effect created by submerged macrophytes is the important basis of ecosystem stabilization and improvement of water environmental quality. So it is necessary to study synthetically the water effect made by submerged maeorphytes on polluted water body. Based on the previous studies and combined with the national "eleventh five" water project—he demonstration project of optimization of hydrophyte community structure in the west of Hangzhou West lake, the paper studying on the efficiency of mcrophytes restoration, the main works are summarized as follows:(1) Studying on the growth law of four submerged maerophytes Potamogeton crispu, Ceratophyllum demersum Kom, Hydrilla verticillata and Vallisneria natans L.Hara in Hangzhou West lake. The submerged mcrophytes in the same water environment were alternated, in addition there are obvious relevance between the differences and the temperature of water. Potamogeton crispu grew vigorous from February to May, the growth speed reached1.018g/(m2·d), Potamogeton crispu was gradually decayed in summer; Hydrilla verticillata grew vigorous from May to August, the growth speed reached0.983g/(m2·d); Ceratophyllum demersum Kom grew at a vigorous rate from March to May, the growth speed reached3.19g/(m2·d); Vallisneria natans grew at a vigorous rate from March to May, the growth speed reached2.701g/(m2·d), and the biomass reached its peak in October.(2) The restoration efficiency of submerged maerophytes with different cropping patterns was studied. The results showed that the survival rates of Potamogeton crispus by sinking is71.1%higher than seeding; the survival rates of Vallisneria by prod cutting is84.3%and87.8%higher than by sinking and seeding, respectively; the survival rates of Hydrilla verticillata by prod cutting is69%higher by seeding, finally the biomass of plant had no significant difference by the three cropping patterns.(3) The biomass of submerged maerophytes were investigated in Maojiabu and Yuhu sublakes, the obvious relevance was observed between the biomass of submerged maerophytes and the biomass of mollusks, The correlation equation y=0.152x-3.2585. Shannon-Weiner index and Margalef index was used to assess the changes in the structure of mollusks communities which in the recovery process of submerged maerophytes communities. The results showed that the pollution was improved when submerged maerophytes communities recovered in Maojiabu.(4) Some resutls can be concluded with5kinds of indices to quantify the ability of competition. The results showed that the ability of competition of Ceratophyllum demersum Kom was stronger than Hydrilla verticillata, finally Ceratophyllum demersum Kom was in the position of absolute dominant resulting in the gradually reduction of Hydrilla verticillata in the plot. The ability of competition have no obvious differences between Vallisneria natans and Ceratophyllum demersum Kom, a symbiotic relationship could be formed between them in a suitable environment.(5) Combined with results, we propose that the submerged maerophytes communities could be recovered in winter when the water was low level, good quality and high degree of transparency. The interference was smaller in winter, and the environment is suitable for submerged maerophytes growth and reproduction. The management should be strengthened after planting submerged maerophytes, especially when the seeds were in sprout, because new plants were easy to float on the water surface. The plants floating on the water surface coukd be salvaged and then planted by cutting method in shallow water areas. That can save the cost and improve the survival.(6) The recovery of submerged maerophytes should carry forward from shallow water to deep water gradually. Shallow water with high transparency was very favorable for new plants. In shallow water areas, setting up a certain scale submerged maerophytes communities and using asexual reproduction can speed up the recovery process. When forming a dominant species in a certain area, species and structures need to be riched and optimized in order to maintain the stability of the submerged maerophytes communities, thereby increase the biological diversity to avoid single species and self-thinning phenomenon.