| Phosphorus is an important limiting factor for algal blooms, the increasing phosphorus loads of water may encourage the growth of algae outbreak to lead to eutrophication.The operation mode of reservoir flood season and fall dry (winter storage summer transfer) forms a huge scale in the reservoir area fluctuating zone, Fluctuating Zone is water ecosystems and terrestrial ecosystems ashore important pastoral zone of the Three Gorge Reservoir, fluctuating zone is reservoir runoff collection area, outcrops of phosphorus runoff water can be deposited into the fluctuating or retention of soil. At the same time, human use can also be brought into the soil with a lot of phosphorus-fluctuating, but in the subsequent flooding of the impact of soil by Fluctuating water flooded the library, erosion, and soil properties will be changed dramatically, leading to the release of phosphorus in the soil into the water body. Therefore, understanding the migration and transformation and release characteristics of phosphorus in the soil fluctuating zone is an important scientific basis for water eutrophication control. In this study there were three typical soils(purple moisture soil, gray-brown and purple soil and mineral-son yellow soil) as the research object, through laboratory simulation experiments to explore the effects of exogenous phosphorus in soil fluctuating zone. The form transformation rules and flooding release characteristics for water eutrophication control, protection of water environment safety Reservoir provides a theoretical basis. The main findings are as follows:1.The characteristics of forms transformation in soil with exogenous phosphorus:(1) With the addition of exogenous phosphorus for soil cultivation, there is a big difference among the trend and magnitude of different forms of phosphorus. Within the range of 10～200 mg-kg-1 of addition of exogenous phosphorus, the order of OP with the added amount of phosphorus with unit increasing:purple moisture soil> gray-brown purple soil> mineral-son yellow soil, the order of IP:gray-brown purple soil> mineral-son yellow soil> purple moisture soil. The content of Fe/Al-P with the added amount of exogenous phosphorus increases linearly, while gray-brown purple soil and mineral-son yellow soil increase parabolicly, Ca-P also increases linearly, the order of Ca-P:mineral-son yellow soil> gray-brown purple soil> purple moisture soil.(2) With increasing amounts of added exogenous phosphorus, the content of Olsen-P increases, there is a obvious transition point mutation with the amount of phosphorus of 20 mg-kg-1, the soil Olsen-P increases rapidly when the amount of exogenous phosphorus added from 20 mg-kg-1 to 50 mg-kg-1, and when the added amount of exogenous phosphorus>50 mg-kg-1, the Olsen-P remaines unchangable, it shows that there is a limit threshold of Olsen-P within the range of addition of exogenous phosphorus. The limit threshold values of Olsen-P of purple moisture soil and gray-brown purple soil are 21.05 mg-kg-1 and 58.68 mg-kg-1, the threshold values in purple moisture soil and gray-brown purple soil are not less than the break point of soil leaching (25 mg～kg-1), there is a higher risk of security presence in the aquatic environment after flooding. Olsen-P content of soil relates with phosphorus forms,Olsen-P of the three soils with TP, OP, Fe/Al-P showes significant positive correlations, while the Ca-P of mineral-son yellow soil only showes to Olsen-P relate in a high significance.(3) Among the three soils, Qm, MBC and K values of mineral-son yellow soil are maximum, minimum is gray-brown purple soil, and the trends are synchronization. Qm and K and correlate with organic matter,Olsen-P and total phosphorus negatively. The DPS of gray-brown purple soil shows the highest,1.20%-11.80%, and mineral-son yellow soil is the lowest,0.14%-1.09%, purple moisture soil is between 0.41%-3.18%, it shows that the release of the risk of gray-brown purple soil is higher than purple moisture soil and mineral-son yellow soil.2. The migration and transformation of soil phosphorus forms during flooding and dry periods(1) The capacity of soil phosphorus to release to overlying waterlogged water bodies vary due to soil type and phosphorus load.Phosphate and TP of overlying water increase with the increasing of flooding time, Phosphate concentration of overlying water increases exponentially, it can be described by CRP<0.45=Ae BPi,To purple moisture soil and gray-brown purple soil, when adding exogenous phosphorus concentration>50 mg.kg-1, the phosphate of overlying water changes greatly, the largest phosphorus is gray-brown purple soil with the amount of exogenous phosphorus of 200 mg.kg-1 (0.82 mg.L-1); when the adding exogenous phosphorus concentration>50 mg.kg-1 of mineral-son yellow soil, in the whole of flooding period, phosphate concentration of water bodies increases with flooding time almost linearly, the maximum amount of phosphorus is with the amount of exogenous phosphorus of 200 mg.kg-1 (0.15mg.L-1); When the adding exogenous phosphorus concentration>50 mg.kg-1 of purple moisture soil and gray-brown purple soil, the TP concentration of overlying water varies widely, the largest phosphorus is gray-brown purple soil with the amount of exogenous phosphorus of 200 mg.kg-1(1.50 mg.L-1). TP Concentration of overlying water can be described by linear equation(CTP=a+bc),with the exogenous phosphorus test range of mineral-son yellow soil, in the 21 days of the flooding period, the TP concentration of overlying water changes greatly, however, after 21 days of flooding period, the TP concentration of overlying water becomes slowly, the largest phosphorus is mineral-son yellow soil with the amount of exogenous phosphorus of 200 mg.kg-1(0.23 mg.L-1).(2) Flooding has changed the soil phosphorus forms, the direction and extent of the conversion constraints of the soil type and phosphorus levels.After a month of flooding period, with the amount of exogenous phosphorus of 200 mg.kg-1, OP of the three soils are all higer than which before the flooding period, the largest increase is the amount of exogenous phosphorus of 200 mg.kg-1 of gray-brown purple soil (21.41%), the proportion of OP in TP increases 5.23%, the largest decrease is mineral-son yellow soil which isn’t with the amount of exogenous phosphorus(54.18%), the proportion in TP increases 11.57%;When the exogenous phosphorus <50 mg.kg-1, flooding makes IP decrease, the largest decrease is the amount of exogenous phosphorus of 10 mg.kg-1 of mineral-son yellow soil (82.40%), the proportion in TP decreases 22.18%,while the exogenous phosphorus> 50 mg.kg-1, flooding makes IP increase, the largest increase is the amount of exogenous phosphorus of 200 mg.kg-1 of purple moisture soil (14.79%), the proportion in TP increases 10.52%; flooding makes Fe/Al-P of gray-brown purple soil increase, purple moisture soil and mineral-son yellow soil decrease, the largest increase is gray-brown purple soil which isn’t with the amount of exogenous phosphorus(366.48%), the proportion in TP increases 20.25%, the largest decrease is the amount of exogenous phosphorus of 20 mg.kg-1 of mineral-son yellow soil (48.26%), the proportion in TP increases 12.13%; flooding makes Ca-P of purple moisture soil increase, gray-brown purple soil and mineral-son yellow soil decrease, the largest increase is purple moisture soil which isn’t with the amount of exogenous phosphorus(16.24%), the proportion in TP increases 3.85%, the largest decrease is the amount of exogenous phosphorus of 20 mg.kg-1 of mineral-son yellow soil(90.28%), the proportion in TP decreases 27.07%.TP and IP, OP, Ca-P show significant positive correlations, the correlation of IP and OP is not significant, the correlation of IP and Fe/Al-P, Ca-P are positive significantly. Olsen-P shows significant positive correlations to TP, IP, Fe/Al-P and Ca-P,while the correlation to OP is not significant.(3) After the dry period of the flooding soil, the soil phosphorus forms has changed. After a month of dry period, gray-brown purple soil and mineral-son yellow soil are higher than which before the dry period, the largest increase is mineral-son yellow soil which isn’t with the amount of exogenous phosphorus(33.56%), the proportion in TP increases 11.85%, OP of purple moisture soil is lower than before the dry period, the largest decrease is purple moisture soil which isn’t with the amount of exogenous phosphorus(20.18%), the proportion in TP decreases 0.25%; Dry period makes the IP of gray-brown purple soil increases a little, the largest increase is the amount of exogenous phosphorus of 10 mg.kg-1 of gray-brown purple soil (3.56%), the proportion in TP increases 11.08%;IP of purple moisture soil and gray-brown purple soil are lower than before the dry period, the largest decrease is mineral-son yellow soil which isn’t with the amount of exogenous phosphorus(53.45%), the proportion in TP decreases 25.31%; Dry period makes Fe/Al-P of purple moisture soil and gray-brown purple soil increase, the largest increase is the amount of exogenous phosphorus of 10 mg.kg-1 of purple moisture soil (56.48%), the proportion in TP increases 5.28%, Fe/Al-P of mineral-son yellow soil decrease, the largest decrease is mineral-son yellow soil which isn’t with the amount of exogenous phosphorus(63.14%), the proportion in TP decreases 16.21%; Dry period makes Ca-P of gray-brown purple equal to before the dry period, purple moisture soil and mineral-son yellow soil decrease, the largest increase is the amount of exogenous phosphorus of 200 mg.kg-1 of purple moisture soil(1.01%), the proportion in TP increases 1.12%, the largest decrease is mineral-son yellow soil which isn’t with the amount of exogenous phosphorus(32.26%), the proportion in TP decreases 6.48%.TP and IP, OP, Fe/Al-P, Ca-P show significant positive correlations, IP and Fe/Al-P, Ca-P are positive significantly. Olsen-P shows significant positive correlations to TP, IP, Fe/Al-P and Ca-P,there is a difference of correlation coefficient between Ca-P content and Fe/Al-P content with Olsen-P, it indicats that there are differences in the correlation between the various forms of phosphorus in different soils and Olsen-P.(4) The Qm of soil are as follows:flooding period>dry period> before the flooding period. After the flooding, the Qm of three soils all increase. The Qm of mineral-son yellow soil which isn’t with the amount of exogenous phosphorus is the largest, gray-brown purple soil with the amount of exogenous phosphorus of 200 mg.kg-1 is the smallest; After the dry, the Qm of mineral-son yellow soil which isn’t with the amount of exogenous phosphorus is still the largest, and gray-brown purple soil with the amount of exogenous phosphorus of 200 mg.kg-1 is the smallest.Compared to before the flooding, the Qm of the three soils increase by 22.22%-33.33%,22.22%-42.86% and 8.33%～25.00%,respectively;After the dry, the Qm of the three soils decrease by 11.11%～22.22%,7.14%-11.11% and 0～16.67%,respectively; It shows that there are differences between different soils,the adsorption capacity of mineral-son yellow soil is higher than purple moisture soil and gray-brown purple soil.(5) After flooding and dry periods, the DPS of three soils all increase with the increasing amount of exogenous phosphorus. After flooding period, the DPS of gray-brown purple soil with the amount of exogenous phosphorus of 200 mg.kg-1 is the largest (9.10%), mineral-son yellow soil which isn’t with the amount of exogenous phosphorus is the smallest (0.20%), the DPS of flooding decrease by 1.24%～21.62%,8.44%-32.76% and 0.82%～14.84%, the largest decreases are all with the amount of exogenous phosphorus of 50 mg.kg-1; After dry period, the DPS of gray-brown purple soil with the amount of exogenous phosphorus of 200 mg.kg-1 is the largest (4.00%), mineral-son yellow soil which isn’t with the amount of exogenous phosphorus is the smallest (0.25%). After the flooding period, Olsen-P relates to DPS positively,and Olsen-P shows significant and negative correlations to Qm, K and PSI, DPS shows significant and negative correlations to Qm, K and PSI; After the dry period, DPS and Olsen-P still correlats positively, Olsen-P shows a significant and negative correlation to Qm, K and PSI, DPS shows significant and negative correlations to Qm, K and PSI, respectively.3. The Migration and transformation of soil phosphorus during reflooding period(1) After a month of reflooding of the dry soil, phosphate and TP of overlying water change with the initial flooding of dynamic variation similarly, but less than the phosphorus concentration of the initial flooding, the relative size of the order of phosphate and TP of the overlying water are:gray-brown purple soil> purple moisture soil> mineral-son yellow soil, the largest phosphate concentration of overlying water is the amount of exogenous phosphorus of 200 mg.kg-1 of gray-brown purple soil (0.57 mg.L-1),and within the range of experimental phosphorus content,the TP concentration of overlying water are all more than 0.02 mg.L-1; Qm of the three soils are higer than the first flooding period, The Qm of mineral-son yellow soil which isn’t with the amount of exogenous phosphorus is maximum, gray-brown purple soil with the amount of exogenous phosphorus of 200 mg.kg-1 is minimum, the increases are 9.09%-50.00%, 0.10%-12.50% and 25.00%～50.00%. The DPS of gray-brown purple soil with the amount of exogenous phosphorus of 200 mg.kg-1 is maximum (6.20%), mineral-son yellow soil which isn’t with the amount of exogenous phosphorus is minimum (0.13%), compared to the first flooding, the increases are 29.06%-97.82%,21.31%-67.60% and 48.33%-74.48%, it indicates that the risk of phosphorus release of three soils after reflooding period all decrease, the decrease of gray-brown purple is the smallest, and the risk of release of gray-brown purple is always the largest, it indicates the risk of phosphorus release of gray-brown purple is largest, mineral-son yellow soil is the smallest once again.(2) The dry soil after the reflooding makes phosphorus forms of soil change.After a month of reflooding period, OP of purple moisture soil is higher than the dry period, gray-brown purple soil and mineral-son yellow soil are lower than the dry period, the largest increase is the amount of exogenous phosphorus of 200 mg.kg-1 of purple moisture soil (15.01%), the proportion of OP in TP increases 0.59%, the largest decrease is mineral-son yellow soil which isn’t with the amount of exogenous phosphorus(43.02%), the proportion in TP decreases 35.02%; IPof gray-brown purple soil and mineral-son yellow soil are higher than the dry period, the largest increase is mineral-son yellow soil which isn’t with the amount of exogenous phosphorus(390.15%), the proportion in TP increases 53.10%,IP of purple moisture soil is lower than the dry period, the largest decrease is the amount of exogenous phosphorus of 50 mg.kg-1 of purple moisture soil (8.17%), the proportion in TP decreases 8.15%;Reflooding makes Fe/Al-P of the three soils increase, the largest increase is mineral-son yellow soil which isn’t with the amount of exogenous phosphorus(200.29%), the proportion in TP increases 11.02%, the largest decrease is the amount of exogenous phosphorus of 100 mg-kg-1 of gray-brown purple soil (3.78%), the proportion in TP increases 1.78%; Reflooding makes Ca-P of purple moisture soil and mineral-son yellow soil increase, gray-brown purple soil decrease, the largest increase is mineral-son yellow soil which isn’t with the amount of exogenous phosphorus(515.05%), the proportion in TP increases 40.62%, the largest decrease is gray-brown purple soil which isn’t with the amount of exogenous phosphorus(4.41%), the proportion in TP increases 0.62%. |
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