Effect Of Emergent Plants On The Circulation Of Nitrogen And Phosphorus Of Eutrophic Lakes

Due to rapid industrial development and growth of population, eutrophication is becoming one of the main water pollution of the world. Phytoremediation is becoming a popular solution because of its low cost and non-pollution, but the research at present just focused on the qualitative analysis and primary quantitative analysis about the effect of the emergent plants on the nitrogen and phosphorus, and the research just lasted for a short period. In this work, Qingnian lake and Aiwan lake were selected as the sampling field to investigate the effect of emergent plants on the removel of the nitrogen and phosphorus from the eutrophic water bodies under different conditions of plant species (including Phragmites australis and Typha orientalis), the plant growth strategy and eutrophic level. The lab-simulating experiments were also carried out to study the ability to absorb the nitrogen and phosphorus by the overground part and the underground part of Phragmites australis and the distribution of the nitrogen and phosphorus in the system.A one year investigation shows that the contents of total nitrogen, total phosphorus, ammonia nitrogen and organic nitrogen in the water were significantly affected by the presence of the plants. During the growing season, the change of the content of total nitrogen was mainly related to that of organic nitrogen. Eutrophic level significantly affected the variation of organic nitrogen content and plant species also played a role. During the decay season, the change of the content of total nitrogen was mainly related to that of organic nitrogen and ammonia nitrogen. Eutrophic level significantly affected the variation of organic nitrogen content and ammonia nitrogen. Variation of the total phosphorus was significantly affected by plant species during both the growing season and the decay season.A one year investigation shows that the contents of total nitrogen, total phosphorus and different forms of nitrogen and phosphorus in the sediment were significantly affected by the presence of the plants. The change of the content of total phosphorus was mainly related to that of organic phosphorus and the conditions of plant species significantly affected the variation of organic phosphorus during both the growing season and the decay season. The change of the content of total nitrogen was mainly related to that of ion exchangeable nitrogen and strong oxidant extractable nitrogen, variation of which was significantly affected by the eutrophic level during the growing season, while was significantly affected by the plant growth strategy during the decay season.Lab-simulating investigation indicated that the cumulant of nitrogen and phosphorus in overground part of the Phragmites australis was 1.9 times and 1.7 times as many as that in underground part. The nitrogen and phosphorus absorbed form the experiment system were distrbuted to the overground part and the underground part with the ratio of 2.1:1 and 1.7:1, respectively. Therefore the harvesting the overground part can greatly bring the nitrogen and phosphorus out of the eutrophication water. The ratio of the content of the nitrogen that accumulated in the Phragmites australis and the content of the nitrogen that was dislodged becaused of the stimulation of the plant-microbe community is 1:9. Therefore, when the Phragmites australis's effect on the eutrophication was estimated, the microorganism contribution must be considered. Accumulation of the Phragmites australis was the only way to remove phosphorus from the aqueous system.