| The paper revieved the vital function of submerged macrophytes in the process of eutrophic lake restoration, the limiting factors of the submerged macrophytes recovery and the important role of the nutrient levels to the submerged macrophytes recovery and growth. On this basis, four kinds of submerged macrophytes:Potamogeton crispus, Vallisneria natans Hara, Hydrilla verticillata Royle and Ceratophyllum demersum, were chosen as research objects to conduct the research at different nutrient levels of Hangzhou Westlake habitat. The research was conducted with various trophic sediments, explored the photosynthetic rate of the four submerged macrophytes at different temperature and illumination intensity, examined the performance of water quality improving through4kinds of the submerged macrophytes in Hangzhou Westlake. Through the study, main results were concluded as follows:1. Potamogeton crispus appeared the best growth state in lake sediment. At the end of the study, the average height of Potamogeton crispus length up to76.81cm,and fresh weight per plant biomass reached1.84g. The resistance of Potamogeton crispus to infertile nutritional conditions was poor, and in the gravel substrate sediment conditions, Potamogeton crispus had grown blocked after40days. Through the study, the most optimum temperature conditions range was15to25℃, and the most suitable light intensity was18000-20000lux, photosynthetic rate could achieve0.485mgO2h-1(g fresh weight)-1in these conditions.2.The plant height and fresh weight of Vallisneria natans was better in the lake sediment conditions than in the other two kinds of sediments such as sand sediment and dredge mud sedimen. As the research was over, the average of plant length reached59.93cm, the average of fresh weight reached13.65g, but under the sand sediment condition the growth was the worst, the average height was only32.2cm, and the fresh weight was only5.57g. The suitable temperature condition for the growth of Vallisneria natans was more than25℃. The light compensation points to it was170lux, the most suitable illumination condition was10000-15000lux, the maximum photosynthetic rate could reach0.307mgO2h-1(g fresh weight)-1in these most optimum conditions,3. Hydrilla verticillata grew best under the dredging sediment conditions. In this situation, the average length of Hydrilla verticillata could reach the:48.74cm, and the fresh weight came up to1.87g, but in the sandy sediment conditions, the growth condition was the worst. At the end, the length of Hydrilla verticillala was only25.14cm, fresh weight was merely0.877g. The appropriate temperature for Hydrilla verticillata growth was25℃, light compensation points was15001ux, the most suitable illumination condition was15000-30000lux, for26℃in temperature, and lighting conditions at25000lux, the maximum photosynthetic rate could reach0.575mgO2h-1(g fresh weight)-1.4. The plant height and fresh weight of Ceratophyllum demersum grew in the dredge sediment conditions was better than in sand sediment and lake sediment. In the dredging sediment conditions, the average length could reach the maximum value:116.77cm, and the fresh weight came up to49.03g, while in the worst condition of soil sediment, the average of plant height was only59cm, biomass and fresh weight was just28.35g. Ceratophyllum demersum optimum growth environment temperature range was15-25℃, and light compensation points was1200lux in this research state, the condition of the illumination more than20000lux was more suitable, but in this study the sun light conditions cannot reach the light saturation point for Ceratophyllum demersum. In theenvironment temperature15-25℃and light conditions40000lux, it could reach the maximum photosynthetic rate:0.531mgO2h-1(g fresh weight)-1.5. The water quality was purified effectively by all kinds of submerged macrophytes and after they were planted, but also showed the significant difference of each other. For the CODMn removal efficiency:Potamogeton crispus (63.3%)>Hydrilla verlicillata (56.8%)> Potamogeton crispus (50.9%)> bitter grass (49.8%); and for the total nitrogen removal effect:Potamogeton crispus (68.9%)> Polamogeton crispus (60.3%)> Vallisneria natans (34.6%)> Hydrilla verticillata (30.8%); the total phosphorus removal efficiency were more than95%of all kinds of the submerged macrophytes plants. But as the submerged macrophytes plants entered into decline period, the nitrogen and phosphorus nutrient adsorbed by the plants would release again, which will lead to water quality deterioration. So when utilization the submerged plants to restore the lakes and rivers, must make good use of growth periodic of plant physiology, and the plants should be harvested before in decline period, avoiding the release of nitrogen and phosphorus nutrients to water again. |
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