Effects Of Vallisneria Natans On Phosphorus In Water Environment

Earth is facing a big challenge of water eutrophication which is mainly caused by overabundance of nitrogen and phosphorus. Many researches indicate that phosphorus is limiting elements of eutrophication which is poor in water; endogenous phosphorus now being a problem in eutrophication control. So endogenous phosphorus in sediment came as a research hotspot recently.Submerged plant which drowned under water with root in sediment and stems and leaves ploating in water, is an important biological group of natural shallow lakes. It is also vital component in water ecological system phase structure:sediment, water body and living beings, is great significance to ecological system, and play an important roll in lake ecological system balance keeping for its structure, Community function and metabolism influences. It is widely used in eutrophic water repairment and ecological system recoverment. Vallisneria natans with characters of breeding fast, growing quickly and developed root system usually being studied for water repairment, so this paper raised a research about effects of V. Natans on phosphorus in water.We imitated a medium entironment of V. Natans, studied its effects on phosphorus fraction and proportion in water, pore water and sediment. Provided a reference for using V. Natans to remediate water quality. Main research contents and results are summarized as follows:1, V. Natans significantly reduce phosphorus fraction in water and pore water, after transplanting of V. Natans, total phosphorus(TP), total dissolved phosphorus(DTP), dissolved inorganic phosphorus(DIP) and dissolved organic phosphorus(DOP) in water range from0.033～0.053mg/L,0.02～0.027mg/L,0.005～0.006mg/L and0.014～0.022mg/L respectively. Particle phosphorus(PP), particle inorganic phosphorus(PIP) and particle organic phosphorus(POP) range from0.011～0.026mg/L,0.003～0.004mg/L and0.007～0.021mg/L. TP, total inorganic phosphorus(TIP) and total organic phosphorus(TOP) in pore water were0.13mg/L,0.09mg/L and0.04mg/L by the end of the study, which were70.10%,72.61%and62.92%to control group respectively. So V. Natans performed well in purify the water quality and increase water clarity, maintain phosphorus in low level.2, V. Natans significantly reduced Moisture Content and Loss on ignition (LOI) of sediment, and reduced total phosphorus(TP) through promoting the mineralize of organophosphates(Org-P) and resolve of calcium phosphorus(Ca-P), TP reduced78.79 mg/kg which count for8.44%of initial content, Org-P reduced49.99mg/kg that contribute62.67%for decreasement of TP. On the other hand, a portion of Iron/aluminum phosphorus(Fe/Al-P) were absorbed for the request of the plant growth,2.99mg/kg and4.10mg/kg decreased respectively, but occluded phosphate(O-P) was not affected(p<0.05). While V. natans grown to highest biomass, it promote settlement of organic matter and formation of Fe-P and O-P, increment were14.82mg/kg and101.53mg/kg respectively, content of Al-P increased7.39%. In a word, V. natans make the phosphorus in water transfer into sediment. The result indicate that effect of V. natans on the leading direction of phosphorus transformation varies with different growth stage, highly reactive phosphorus was absorbed and accumulated in plant as stable fraction during rapid growth stage, adsorption capacity of sediment increased during slow growth stage, phosphorus settlement was promoted.3, When Seeding stage V. Natans cultivated in0mg/L phosphorus, it released phosphorus to water, but when in0.02mg/L and0.05mg/L, drasticly adsorption happened in the first0.5h, adsorption speed were12.0μ g/L·h-1and18.7μ g/L·h-1, but drasticly adsorption happened in the0.5-1h when cultivated in0.1mg/L.0.013mg/L maybe threshold of adsorption, and there was a concentration among0.05-1mg/L that distinguish high affinity binding and low affinity binding according to DO, pH and EH.Growing stage V. Natans absorb speed has a positive correlation with phosphorus concentration, requirement and phosphorus fixation ability increased than seeding stage, threshold reduced to0.01mg/L. Declining stage V. Natans stopped absorb phosphorus, releasement instead of absorption, release speed increase as phosphorus concentration decreases.