Impact Of Environmental Factors And Submerged Plant On Phosphate Release From Sediment

Eutrophcation of surface water system is a serious environmental problem in the world. The major factors causing water eutrophication include load of nitrogen (N) and phosphors (P), particularly P. Phosphorus release in sediment plays important roles in supporting algae growth and promote lake eutrophication. However, release and sorption of phosphorus by the sediment are controlled by many factors, including physico-chemical characteristics of sediment and other environmental conditions, such as redox potential, pH, temperature and so on. With the selected Huajia Pool as the representative of the eutrophicated lakes, the objectives of this study were to examine the characteristic of sediment, P release as affected by environmental conditions, and effect of growing submerged plant on P release from the sediment. The results of this study could provide scientific bases for controlling the lake eutrophication. The main results obtained are summarized as follows:1. Phosphorus fractions in sediments are investigated mainly by using the method named "SMT (the Standards Measurements and Testing Program of the European Commission) Protocol", the newest international current classification method of phosphorus. The results showed that major P fractions in the sediment included inorganic phosphorus (IP), organic phosphorus (OP), non-apatite inorganic phosphorus (NAIP) and apatite phosphorus (AP). Two fractions of OP and NAIP exhibited greater potentials of phosphorus release than others. The inorganic phosphorus accounted for 80-95% of the total P content in Huajia pool sediment, and the apatite phosphorus (AP) is the main form of the IP, which accounted for 75-90% of the total P in the sediment,2. A pilot experimental study showed that the dissolved oxygen(DO), pH, temperatures, disturbance, height of overlying water and coverage of the container affected P release rates from the sediment. Phosphorus release rate from the sediment washighest at high pH and smallest at neutral pH conditions. Anoxic condition (oxygen deficiency) stimulated P release, while the aerobic condition could inhibit the P release from the sediment. The increase in temperature, disturbance of the water and increasing height of overlying water influenced P release from the sediment. Covering sediments decreased P release from the sediment, but it will threaten the ecosystem. The pH and DO are the most important factors affecting P release from the sediment.3. Submerged plants play a key role on the control of nutrient release from the sediment, especially phosphorus. The results showed that planting Elodea canadensis L., Myriophyllum spicatum L. and Vallisneria gigantean L. decreased P release from the sediment and nutrient concentration in the water. Among the three plant species, Myriophyllum spicatum L. showed greater effectiveness in inhibiting P release from the sediment than Elodea canadensis L.and Vallisneria gigantean L.. In the shallow lakes, it is of practical value to revive submerged plants like Myriophyllum spicatum L. in the sediment under the conditions with greater disturbances in lake, for the control of phosphate release from the sediment. As floating aquatic plants can't grow in winter at low temperature, planting submerged plants play a key role in stabilizing the water quality.4. Physical measures alone can not control the release of nutrients from the sediment, whereas aquatic plants especially submerged plants can absorb nutrients and control the nutrients release from the sediment and reduce nutrient concentration in water body. The results from this study indicate that phyoremediation with submerged plants is likely to be a promising technology of solving internal pollution of the lake sediment.