| The Three Gorges Reservior has attracted worldwide attention, with flood control, power generation, shipping and other comprehensive benefits, which is the backbone of the project for governing and managing Yangtze River. The Three Gorges Reservior were built in June2003, completed the phase Ⅱ water storage on October2006and Phase III experimental water storage of175m water level on November2008. It reached the175m water level design goals for the first time on October26,2010. After the first water storage, the Three Gorges Reservoir showed many problems including water eutrophication and algal blooms. Phosphrus is a key limiting factor as to algae population and density. The increasing of phosphorus can leads to algae growing. Since the cyclical operation of Three Gorges Reservoir and the annual water level drop up to30m, the soils and sediments on the shore will accumulate a large amount of phosphorus gradually and may easily release back into the water again. As it is the largest reservoir in our country and its off-season flooding and drying (winter store and summer drain), plus the wide distribution of water level fluctuation zone, it is necessary to estimate phosphorus content in soils of the Three Gorges Reservoir areas. These will help to explore the impacts of phosphorus cycle system on the reservoir ecological environment and reveal the impact factors of phosphorus pools. Therefore, in this paper, basing on areas of water-level fluctuation zone, soil types, land-use, gradient and others,521soil and sediment samples were collected (including180m un-watered height), estimating phosphorus pools and constituent. The conclusion of this research obtained as follows:1. Characteristics of phosphorus distribution in soils of water-level fluctuation zone(1) The total phosphorus content in soils(sediments) of the Three Gorges Reservoir areas is60.04mg·kg-1-2271.31mg·kg-1, with mean value is (502.37±204.92)mg·kg-1The phosphorus content of soils are60.04mg·kg-1-1157.04mg·kg-1, with mean value is (484.27±206.85)mg·kg-1; the phosphorus content of sediments are131.15mg·kg-1-1078.78mg·kg-1, with mean value is (523.08±152.53) mg·kg-1.(2) From the point of administration areas, different parts of the total phosphorus content showed a larger difference. The total phosphorus content is higher in Changshou and Fuling, reaching (699.13±169.16)mg·kg-1and (633.57±217.11)mg·kg-1. From the point of watershed location, the maximun mean value of total phosphorus in main stream shows up in Yunyang water-level fluctuation zone, the minimum value shows up in Fengjie water-level fluctuation zone; the maximum mean value of total phosphorus in tributary shows up in Changshou water-level fluctuation zone, the minimum shows up in Kaixian water-level fluctuation zone; the maximum mean value of total phosphorus in junction stream shows up in Fuling and Changshou water-level fluctuation zone, the minimum value shows up in Zhongxian water-level fluctuation zone. From the point of different height, the phosphorus content of150m height is relatively the highest.(3) As to different soil types, the total phosphorus content in water-level fluctuation zone in descending order is purple soil> yellow calcic soil. From the point of different slope, the total phosphorus content decreases with the increasing of slope. The total phosphorus content are different as various land-use. The mean value in descending order is farmland> grassland> others(mainly wasteland)> woodland.2. Phosphorus poolsUsing GIS and checking areas of the water-level fluctuation zone, phosphorus pools under each administration areas and heights were estimated, which shows that the phosphorus pools in20cm surface layer soils and sediments of the Three Gorges Reservoir areas is43058.04t, and the biggest is Fuling(7685.26t), the smallest is Shizhu(1052.56t).Phosphorus pools are diverse among different administration areas and heights,145m-155m water-level fluctuation zone is15702.42t, accounting for36.47%of the total, and Fuling is the biggest(3298.81t), Changshou is the smallest(145.95t).155m-165m water-level fluctuation zone is13827.87t, accounting for32.11%of the total, and Fuling is the biggest(2506.65t), Shizhu is the smallest(281.58t).165m-175m water-level fluctuation zone is13527.74t, accounting for31.42%of the total, and Kaixian is the biggest(2965.15t), Shizhu is the smallest(249.29t).3. Phosphorus forms in soils (sediments) of water-level fluctuation zoneBasing on the results of phosphorus forms of typical samples, Ca-phosphorus is the main forms, followed by organic phosphorus, and Fe/Al-phosphorus is the least. Organic phosphorus content is91.65mg·kg-1-859.84mg·kg-1, accounting for32.70%-94.77%of the total phosphorus; Fe/Al-phosphorus content is11.18mg·kg-1-299.87mg·kg-1, accounting for3.81%-55.95%of the inorganic phosphorus; Ca-phosphorus content is61.32mg·kg-1-635.77mg·kg-1, accounting for44.05-96.19%of the inorganic phosphorus; organic phosphorus content is29.11mg·kg-1-381.310mg·kg-1, accounting for5.23%-67.30%of the total phosphorus4. Factors associating with phosphorus formsAccording to typical samples which detected different forms of ferrum, aluminum, manganese, dissolved organic matter content and its UV-Vis spectral characteristics, we can evaluate the relationship between soil physicochemical properties and the occurrence of phosphorus in soils and sediments. The phosphorus forms have something to do with pH, organic matter, dissolved organic matter, ferrum, aluminum and manganese, which as follows:Total phosphorus is negatively correlated with pH, and shows a significant positive correlation with organic matter; Fe/Al-phosphorus shows a negative correlation with pH, but has a positive correlation with organic matter; both organic phosphorus and Olsen-p have a significant positive correlation with organic matter.There is a connection between total phosphorus, inorganic phosphorus, Fe/Al-phosphorus and dissolved organic matter content. According to the relationship between total phosphorus, inorganic phosphorus, Fe/AI-phosphorus and S value of UVA, UVB, UVC, UVR, it suggests that organic matter with higher molecular weight, degree of humification, hydrophobic component and a higher aromatic structure have a positive connection with total phosphorus, inorganic phosphorus, Fe/Al-phosphorus in soils and sediments.Moreover, from the connection between phosphorus and metal, metal oxide, it indicates that total phosphorus, inorganic phosphorus, Fe/Al-phosphorus has a positive correlation with amorphous ferrum, ferrum binding to organic matter, whereas organic phosphorus has a positive correlation with aluminum/manganese binding to organic matter.5. Olsen-P content and the risk to water environmentAll the Olsen-P in soils and sediments were detected to evaluate the impacts of phosphorus on water in the Three Gorges Reservior areas. Since soil and sediment are affected by periodic flooding and other environmental changes in the Three Gorges Reservoir areas, there is a big difference of phosphorus content in the spatial distribution. The results show that there are38.98%of the samples contain less than10mg·kg-1, which means a very small impact on the water environment;34.16%of the samples contain10mg·kg-1-20mg·kg-1, which means a slight impact on water environment;22.65%of the samples contain20mg·kg-1-40mg·kg-1, which means a larger risk of phosphorus releasing to water, and these regions should be regarded as general precautionary area;2.69%of the samples contain greater than50mg·kg-1, meaning phosphorus in these regions are easily enter into water through leakage or runoff.In summary, this study reveals phosphorus occurrence and characteristics in soils and sediments of the Three Gorges Reservior areas, which providing basic data for researching the impacts of phosphorus on the water. |
PDF Full Text Request