Effectiveness Of Purification Of Eutrophic Water By Three Aquatic Plants And Its Influencing Factors

Nowadays, water eutrophication has becoming a worldwide difficult problem, how to solve it is a hot point around the world. Phytoremediation is becoming a popular solution because of its non-pollution, low cost and ecologically sound. A lot has been studied ahout aquatic macrophytes and their application to phytoremediation, however, less information is available about the systematic researches on effectiveness of purification by different floating aquatic plant species with relation to their growth characteristics and environment factors. The objectives of this paper were to compare the effectiveness of purification of eutrophic water by different aquatic plant species (Alternanthera philoxeroides, Myriophyllum spicatum, Jussiaea stipulacea Ohwi) and the influencing factors. The main results are summarized as follows:1. The results showed that growth responses to low nitrogen and phosphorus concentration were different among the tested floating plant species. The lowest nitrogen and phosphorus concentrations for the plant to stop growth was N:0.05-0.1mg/L; P:0.01-0.02mg/L for Myriophyllum spicatum(M), whereas N:0.1-0.2mg/L; P: 0.005-0.01mg/L.for Jussiaea stipulacea Ohwi(J). Both floating aquatic plants can grow in relative low N and P water body. Myriophyllum spicatum has a better endurance to low N but less durable ability to low P, as compared to Jussiaea stipulacea Ohwi.2. The results indicated that Myriophyllum spicatum had a maximum biomass at water body with N/P ratio of 2:1, while Jussiaea stipulacea Ohwi had best growth at N/P ratio of 10:1-20:1, and Alternanthera philoxeroides grew best at N/P ratio of 20:1-40:1. At low levels of N and P water body, nitrogen was the limiting factor for growth of Alternanthera philoxeroides, Jussiaea stipulacea Ohwi, but phosphorus was the limiting factor for growth of Myriophyllum spicatum. The nitrogen and phosphorus accumulation by the plants showed a similar pattern as biomass with relation to N/P ratio. Field experiments showed that the biomass, nitrogen and phosphorus accumulation of Jussiaea stipulacea Ohwi and Myriophyllum spicatum corresponded well with the patterns of "S".3. Experiment show different contribution of plants and microbial in different treatment. The treatment to nitrogen removal efficiency: Myriophyllum spicatum> Jussiaea stipulacea Ohwi. > Alternanthera philoxeroides. , but to phosphorus removal efficiency is Myriophyllum spicatum> Alternanthera philoxeroides.>Jussiaea stipulacea Ohwi. Alternanthera philoxeroides, Myriophyllum spicatum, Jussiaea stipulacea Ohwi had positive effect (32.60%, 35.64%, 34.22% respectively) on the plant-enhanced microbial removal of nitrogen, because the plants had stimulative effect on nitrogen metabolic microoganism. However, the plants had negative effect on phosphorus metabolic microoganisms.4. Myriophyllum spicatum, Jussiaea stipulacea Ohwi had broad ranges of adaption to temperature and pH. They showed better growth at the temperature of 20℃-30℃and neutral pH (pH≈7). Temperature had the same effects on biomass of both plant species. The removal of total nitrogen and total phosphorus decreased with decreasing of temperature: 30℃>20℃>10℃.5. According to the observation and testing under field condition yearround, we found that Myriophyllum spicatum, Jussiaea stipulacea Ohwi had effective removal of nutrients from eutrophic water body for over 8 months per year. Myriophyllum spicatum had effective nutrient removal abilities in most time of a year, from March to December. So both plant species had a great potential for application in phytoremediation engineering of eutrophic water body.