Study On Forms,Release Rules And Control Measures Of Internal Phosphorus And Nitrogen In Chaohu Lake

In certain condition,internal N and P can be released to water,which can sharpen eutrophication.Therefore,internal N and P would play a key role in the lake restoration after external N and P load reduction. Taking Chaohu lake sediment as the object,the paper studied the forms of internal N and P ,the rule of release and the control measures in simulated laboratory conditions,which supported by National Natural Science Foundation of China(50379003), Natural Science Foundation of Anhui Province(01045201) and Superior Youngth Foundation of Anhui Province(200137).(1) The sediment was sliced (0-25cm),whose TN,TP,pH and organism were measured . The results showed that the amount of TP decreased with sediment depth, the content in the deepest layer was 172.95 mg/kg, that reached 732.51 mg/kg in the surface layer. Contrarily, the amount of TN incressed with sediment depth.(2) Different phosphorus forms in sediments were analyzed using sequential extraction scheme ,which was brought up by LiYue. The phorphorus was separated into seven forms as follows: pore water phosphorus,loosely sorbed phosphorus and CaCO₃ associated phosphorus , aluminium bound phosphorus , iron bound phosphorus, closed phosphorus, calcium bound phosphorus, apatite and other inorganic phosphorus, organic phosphorus. The contents of these phosphorus forms were1.59%,3.51%,30.99%,2.43%, 20.27%,18.25%,22.96% respectively. Iron-bound phosphorus was the dominant form in the sediments.The concentration of total nitrogen is higher in the west side than that in the east side in Chaohu Lake,the spatial distribution trend of ammonium nitrogen, organic nitrogen and nitrate and nitrite were the same as total nitrogen.Very close linear relations existed between organic matter and organic phosphorus, total nitrogen, iron bound phosphorus + aluminium bound phosphorus.(3) The article analyzed the influence of phosphorus content in overlying water on internal phosphorus release,and stressed to research the effects of environsmental conditions(illumination, pH, temperature, dissolved oxygen levels, microorganism, disturbtion and water content of sediment) on internal phosphorus release. The result indicated that the effect of phosphorus release while distilled water as overlying water was obvious than lake water;the maximum phosphorus released under illumination was smaller than that without illumination, the difference was 1.81 mg/kg;Very closeparabola relations existed between the maximum phosphorus released and pH the equation was:y=2.9642x2-39.166x+139;the maximum phosphorus released was highly correlated to temperatures:y=0.5235x-1.7733;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 1.97times as much as that without being disturbed and the rate of release was high;The release of P was suppressed under aerobic condition.the amount of released internal P in anaerobic under the same pH was about 9.16 times as much as that in aerobic;the amount of released internal P was maxium in alkalinity,followed under acid condition,minium in neutral condition.(4) Very close linear relations existed between TP and Fe in the overlying water on the releaseing process;the experiment studied the stability of P under the different pH values and DO levels. The results showed the release of aluminium bound and iron bound phosphorus were promoted under alkaline and anaerobic conditions , calcium bound phosphorus are responsible for the phosphorus release under acid condition.(5) The effects of environmental factors on NH/ release in sediment slurries from Chaohu lake were studied under a laboratorial control condition.The results showed that when temperature was increased and concentration of NH4+ in overlying water was decreased, NH^ released from sediment increased with similar trend;pH had complex effect on NH4+ release. In anaerobic, the release amount of NH/ was 6 times as much as in aerobic?(6) Aluminum chloride and ferric chloride were tested to control internal P release,the results showed that when pH varied from 7 tolO,the effective dosage of aluminum chloride and ferric chloride increased from 30 mg/L to 50mg/L and From 12.5 mg/L to 25.0 mg/L respectively, both the effects of aluminum chloride and ferric chloride at pH=4 were not significant.