| Three Gorges Progect operated in2003, it used the "non-flood season dammed-up water to power generation, and flood season discharge water and sand" water level scheduling way yearly, and every year in October it bagan storing water, and it reached the highest water level175m in December to January, and the lowest water level145m from June to September, this lead to a30m vertical drop in the three Gorges Reservoir, an area of437～446km2water level fluctuation zone(WLFZ).The WLFZ was a special wetland ecosystem, periodic water level fluctuation and the effect of artificial factor, caused the change of soil property and a series ecological problems, and these problems not only affect the safe operation of the three gorges reservoir, but also directly affect the water environment security of the economically developed areas in the middle and lower reaches of the Yangtze river. Previous studies focus on the efficient use of land more, the soil properties change after flooded-dry-flooded and suitable plant selection, etc., but less focus on the bio-availability of soil phosphorus and the phosphorus fixation method research. Therefore, in this paper, the three Gorges Reservoir area soil was selected as the research object, pot experiment was employed to study bio-availability of soil phosphorus, indoor simulation methods was employed to study the soil phosphorus release under different conditions such as pH, temperature, and disturbance, as well as by adding substances to study phosphorus fixation and morphological changes of available phosphorus in soil. Aimed at reducing the available phosphorus content of the soil, reducing eutrophication occurrence probability, thus ensure the security of the three gorges reservoir ecological environment. The main conclusions were as follows:①Pot experiment showed that, within the scope of30～210mg/kg phosphorus application level, lettuce yield increased significantly with the application rate of phosphoric fertilizer, compared with treatment2(NP0K), the yield increased by78%～174%, indicates that with the same application of nitrogen and potassium, increase phosphate fertilizer can improve the yield of lettuce. In different phosphorus levels, the total phosphorus content of stem was more than that of leaf, total phosphorus content of stem increased gradually with the increase of phosphorus levels, and control9(NP210K) content was the highest (13.3g/kg),60%higher than that of treatment2(NP0K),while the phosphorus content in leaves has no obvious difference between the controls. In different phosphorus application, leaf phosphorus uptaken was greater than that of stem, and both were significantly higher than that of treatment2(NP0K), suggested that phosphorus application helped lettuce phosphorus absorption. Compared with the control, the content of Ca2-P, Ca8-P, Al-P and Fe-P increased with the increasing of application rate of phosphorus, and the content of control9was the highest, but O-P and Ca10-P between the groups had no difference. Through the correlation analysis of various forms of inorganic phosphorus in soil under different controls and phosphorus uptaken in lettuce stem and leaf, indicated that the lettuce stem phosphorus uptaken had extremely significant relation with Fe-P and Ca2-P, and correlation coefficient were0.946and0.874, and Al-P reached significant level, correlation coefficient were0.673, and lettuce leaf phosphorus uptake was only significantly correlated with Fe-P content, and correlation coefficient were0.674.Through different phosphorus application levels, correlation analysis between various forms of inorganic phosphorus and lettuce phosphorus uptaken, lettuce plant height,yield of lettuce showed that the bio-availability of different inorganic phosphorus was:Fe-P> Ca2-P> Al-P> Ca8-P> O-P, Ca10-P.②In the Flood situation, soil phosphorus release had bigger difference under different pH, temperature, disturbance treatments, phosphorus release of pH=3, pH=9, pH=11treatment was higher than that of control (pH=6), reached62%,333%and669%,respectively, compared with control, phosphorus release under neutral condition (pH=7) and the acidic condition (pH=5) treatment was6%,36%respectively less than that of control; Under different temperature condition, soil phosphorus release significantly increased by the increase of temperature, under35℃treatment phosphorus release was10%higher than that of20℃,5℃treatment phosphorus release was46%lower than that of20℃. In the disturbance situation, the total phosphorus release was18%lower than that of no disturbance, but after25days soil phosphorus release quantity under disturbance gradually higher than that of control. Therefore, peracid, parlkaline, relatively high temperature and long time disturbance will increase the soil phosphorus release quantity.③Different pH, temperature and disturbance had great influence on soil inorganic phosphorus forms. Compared with CK, different pH treatment increased total inorganic phosphorus in soil, the total soil inorganic phosphorus under alkaline control (pH=9) was the highest,21%higher than CK, soil inorganic phosphorus increased by16%and8%respectively under acidity treatment (pH=3, pH=5) and neutral treatment (pH=7). For various forms of inorganic phosphorus in soil, acidic conditions (pH=3, pH=5) availed the accumulation of Fe-P and O-P, neutral condition (pH=7) for Al-P and O-P, and alkaline conditions (pH=9, pH=11) for Ca2-P, Al-P and O-P. Under the different temperature treatments,35℃treatment was the highest,24%higher than control, and availed the accumulation of Ca2-P, Al-P, O-P and Ca10-P. External disturbances increased soil inorganic phosphorus by16%, and also increased various forms of inorganic phosphorus accordingly.④Adding extra substances can decrease the content of available phosphorus in soil, through indoor simulation experiment showed that adding ferric chloride and lime can reduce the content of available phosphorus in soil, especially ferric trichloride, T1(soil:extra=1:0.25), T2(1:0.5), T3(1:0.75)treatment significantly lower than control, reduced by92%,96%,98%respectively.Adding lime S3(1:0.75) and silicon slag G3(1:0.75) also reduced the content of available phosphorus in soil, reduced by17%and5%respectively than control, however adding the low and medium proportion of silicon slag would increase the available phosphorus content in the soil. With the biomass ash (sawing wood ash) ratio increased, we did not achieve the desired phosphorus fixation effect, on the contrary, it increased available phosphorus in soil, phosphorus content of H1, H2, H3treatment increased by516.6mg/kg,648.3mg/kg and691.4mg/kg respectively. On the same adding ratio conditions, phosphorus fixation effect of ferric trichloride was the best among the lime, silicon slag and sawing wood ash, especially under high proportion condition, the effect is more obvious.⑤Adding different extra substances had different effects on soil inorganic phosphorus forms. Ferric trichloride treatment(T1, T2, T3) significantly reduced the total inorganic phosphorus, decreased by26%,46%,46%respectively compared with control, and obviously reduced Ca2-P, Al-P, Ca10-P among the various forms of inorganic phosphorus. For silicon slag treatment(G1,G2,G3) reduced the total inorganic phosphorus, decreased by33%,39%,35%respectively compared with control, and G2treatment effect was best, and main inhibited the accumulation of Ca10-P, Fe-P and Ca2-P. Lime S1, S2, S3treatment inhibited the accumulation of inorganic phosphorus, S3treatment effect was the best, and inhibiting effect of the various forms of inorganic phosphorus was:Al-P> Fe-P> Ca8-P> O-P, Al-P reduced by103%compared with control. Sawing wood ash did not effectively inhibit the inorganic phosphorus accumulation, whereas increased soil inorganic phosphorus content. Ferric trichloride mainly reduced Ca2-P, Al-P and Ca10-P, lime mainly reduced Al-P, Fe-P, Ca8-P and O-P, silicon slag mainly reduced Ca10-P, Fe-P, Ca2-P, O-P. Above all, four kinds of extra additives, iron trichloride treatment was best, but considered the influence on sediment and the microbial community in high content of FeCl3, based on the characteristics of water environment, selected the content between control and T1or content between T1and T2. |
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