| With the development of Rare earth (RE) industry in China, especially the widely used in agriculture, a mass of RE have been transferred from lithosphere to hydrosphere and biosphere. Sichuan is a province with rich resource of RE, the existed research showed that the concentration of RE in Yangtze River (Sichuan basin) was50times than the average of world’s fresh waters, some RE concentration in low flow period was even near to100μg/L. On the other hand, after the built of Three Gorges Dam, Yangtze River in Sichuan had changed from natural river course to seasonal adjusts reservoir, the hydraulic conditions had been a huge change in the reservoir area, whether these changes could lead to the eutrophication and algal bloom was widely discussed. The ecological status of Sichuan Province is more and more important.Based on the two theories, Spirodela Polyrhiza, which was common in Sichuan and easy to lead to eutrophication, was selected for research. The controlled experiment was used for the observation of fresh weight, chlorophyll a, carbonic anhydrase activity and photosynthetic rate in different Ce3+concentration, meanwhile, we assayed the culture solution condition. The results showed that low concentration of Ce3+can promote Spirodela Polyrhiza’s growth, increased chlorophyll a content, carbonic anhydrase activity and photosynthetic rate. Fluorescence analysis on chlorophyll showed that fluorescence yield of chlorophyll in low concentration was higher than the blank. Strong metabolism result in TN/TP in culture solution decline rapidly, the changes rate of COD (rise) and DO (decreased) were both faster than the blank and the high concentration samples. All the physiological indexes in high concentration of Ce3+we measured were restrained. We choose the data of fresh weight, chlorophyll a content and carbonic anhydrase activity in the9th day for quadratic fit with SPSS, and calculated the most promote Ce3+concentration was near0.60mg/L.Because temperature has a strong influence on Spiodela Polyrhiza in nature water, we observed the fresh weight’s variation tendency in15days which fostered in Ce3+0.60mg/L. When temperature was below10℃, Spiodela Polyrhiza was dormant, and the fresh weight variation was near0, the temperature was above10℃, Spiodela Polyrhiza grew better with temperature rises. When the temperature rise to35℃, the fresh weight of Spiodela Polyrhiza increased greatly in the first3days, then showed a steady decline in the last days, at the9th day, the weight even lower than the weight in5℃. The preliminary analysis of the variation tendency in35℃was nutrient substance in the culture solution cannot be replenished after the depleted in the static controlled experiment. Generally, the growth of Spiodela Polyrhiza was better with the increase of temperature when above10℃.In addition, the promotion of Ce3+on Spiodela Polyrhiza mechanism was preliminarily studied, it was mainly focused on calcification effect. By setting samples lack of Ca2+or Ce3+, we observed the changes of chlorophyll a, Mg2+-ATPase and chlorophyll fluorescent characteristic in different samples. The results showed that the three physical signs in the sample lack of both Ca2+and Ce3+were lower than the other samples, and the physical signs in the sample only lack of Ca2+were similar with the sample only lack of Ce3+. This experiment affirmed the calcification effect was one contributing factor.We hope these experiments can provide scientific proof on prevention against eutrophication and algal bloom. |
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