The Research Of Wabuhu Lake Sediment On Internal Phosphorus Forms, Release And Control Measures

Wabuhu lake sediment was the object of this experiment, which made research on forms of internal phosphorus, the rule of release and control measures.The artilcle included:The sediment was sliced then total-nitrate, total- phosphorus,NH4⁺-N,NO₃^--N and organism were measured .The results showed that the amount of total-phosphorus decreased with sediment depth, the content in the deepest layer was 311.98 mg/kg, that reached 584.32 mg/kg in the surface layer. Contrarily, the content of total-nitrate in the surface layer is lower than that of the deepest layer. Which was due to the release of NH3 when the surface sediment was exposed .Nitrification was weakened with increasing depth, which favored the accumulation of the NH4⁺-N. the content of NH4⁺-N in the surface layer is 10.024 mg/kg, that of the deepest layer is 28.238 mg/kg. But the content of NO₃^--N decreased with increasing depth, the content in the surface layer was 6.211 mg/kg, that of the deepest layer was 2.324 mg/kg.Different phosphorus forms in sediments were measured using sequential extraction scheme presented by LiYue. The phorphorus was separated into : pore water-phosphorus,loosely sorbed -phosphorus and CaCO₃ associated phosphorus aluminium bound iron bound closed phosphorus calcium bound The contents of these phosphorus forms are 1.45% 5.66% 32.12% 2.60% 22.30%respectively . Iron bound and calcium bound phosphorus may act as the main source of internal phosphorus contributing to the eutrophic lake.The article analyzed the difference of phosphorus release between dried and fresh sediment from Wabuhu lake, discussed the effects of environmental conditions(illumination pH values temperature dissolved oxygen levels microorganism and disturbtion) on the release experiment. The datum indicated that the effect of phosphorus release in fresh sediment was obvious than of dried sediments;the maximum phosphorus released under illumination was smaller thanthat without illumination, the difference was 1.42 mg/kg;Regression analyses of the maximum phosphorus released and pH values revealed a significant parabola relationship, the equation was: y=3.0057x2-39.371x+139.2;the maximum phosphorus released were highly and positively correlated to temperatures, y=0.473x-1.2867;Under oxic condition, the sediment can release phosphorus into the water, but the phosphorus levels and the release intensity were much smaller than those under anoxic condition;microorganism could promote the internal phosphorus release;The maximum phosphorus released under strong disturbtion was twice as much as that without be disturbed and the rate of release was high, there was no significant effect of weak disturbtion on phosphorus release;The release of phosphorus was inhibited under oxic condition but the inhibition of oxic condition is tightly related with the pH values and had a high effect while the pH is at 7;but the effect of pH 10 was not as significant as that of pH 7;The release of phosphorus was boosted significantly under anoxic condition at pH 7.Regression analyses of the concentration of Fe and phosphorus in the overlying water revealed a significant linear relationship in the experiment of phosphorus release. Futhermore, the experiment studied the stability of phosphorus under the different pH values and DO levels. The datum indicated the release of aluminium bound and iron bound phosphorus were promoted under alkaline and anoxic conditions , calcium bound phosphorus are responsible for the release of phosphorus under acid condition.Aluminum chloride and ferric chloride were tested to control internal phosphorus release, the results showed that when pH value varying from 7 to 10, the effective dosage of aluminum chloride and ferric chloride increased from 25 mg/L to 45 mg/L and from 12.5 mg/L to 22.5 mg/L respectively, both the effects of aluminum chloride and ferric chloride at pH 4 were not significant.