| With the increase in population and rapid economic development, the pollution of fresh water in China is becoming more and more serious. Our country already have a number of lakes in the eutrophication level because of much nourishment poured into water, so the technology of reconstruct underwater ecosystem through restore aquatic plant communities have been widely focused by researchers. But because its costs are higher as the plant completely submerged under water, also the roots are easy to be damaged when they are transplanted and the various pollution stress in eutrophic water may be exceeded the threshold to submerged plant, bring many unfavorable factors to the project. So this research focuses on the development of modular plant which applied in eutrophic water, the optimal biomass of modular plants and the optimal ratio of modular plant combination. The exploration of this technology will contribute to ecological restoration the eutrophic water and provide scientific basis for its.The main objects of modular plants in this study are Vallisneria natans, and the concrete research content includes: The response of modular Vallisneria natans to nitrogen stress, the effects of modular Vallisneria natans biomass on water quality, the effects of modular Vallisneria natans and Elodea nuttallii combination on water quality. The methods and results are shown as follows:(1) The effects of nitrogen stress on growth and physiology of modular plants under six nitrogen levels were studied. The nitrogen levels were 0mg/L,5mg/L,10mg/L,25mg/L,50mg/L,100mg/L and named T0,T1,T2,T3,T4,T5. The results showed that: The highest biomass growth rate at 5mg/L was 15.52%, when TN concentration was more than 5mg/L the biomass growth rate increased with increasing TN concentration. The growth rate had a negative growth when TN concentration was more than 50mg/L. The TN concentration from 5mg/L to 10mg/L can increase the chlorophyll content of Vallisneria natans, but the high concentration of nitrogen had no significant effect on the chlorophyll content, and the highest chlorophyll content at 5mg/L was 1.58 times as Initial content; When TN concentration was more than 50mg/L the NP close to 0 and the highest NP at 5mg/L was 0.22 mg O2FW-1 g-1h-1; With the increase of TN concentration from 5mg/L to 25mg/L, on the first day, the activities of POD decreased, the activities of CAT increased, the activities of SOD increased from 5mg/L to 10mg/L and then decreased from 10mg/L to 25mg/L; On the seventh day, the activities of POD,CAT and SOD were all first increased and then decreased, and the highest activities at 10mg/L, pod was 117.6U/mgprot, CAT was 4.13 U/mgprot, SOD was 9.97 U/mgprot.(2) The effects of modular Vallisneria natans biomass on water quality under six biomass levels were studied. The biomass levels were 0g,81 g,162g,243 g,324g,405 g,486g and named V0,V0,V1,V2,V3,V4,V5,V6. The results showed that: With the increase of modular Vallisneria natans biomass, the removal rate of TN, NH4-N, TP, and CODMn increased gradually. The highest removal rate of TN, NH4-N, TP, CODMn was 92.24%, 67.50%, 83.14%, 47.48%; When modular Vallisneria natans biomass was more than 324g(1296g/m2) the removal rates of TN and TP were slow down, and the highest biomass growth rate at 324g; According to ANOVA, the TN, NH4-N, TP, and CODMn in the experimental group were significantly lower than those in the blank group(p﹤0.05); In the removal of TN and TP, the experimental group V4 was significantly different with the experimental group V1, V2 and V3(p﹤0.05), but it not significantly different with V5 and V6(p>0.05), so the best biomass was 1296 g/m2.(3)With the total biomass was 324 g, the effects of modular Vallisneria natans and Elodea nuttallii combination on water quality under five biomass ratio levels were studied. The biomass ratio levels were 0g:324g,108g:216g,216g:108g,324g:0g and named A,B,C,D, and another set of blank control group named E. The results showed that: all the biomass ratio levels were useful to purge water, the highest removal rate of TN, NH4-N, TP, CODMn was 93.86%, 72.89%, 91.13%, 49.21%; According to the regression equation, the removal ability of TN and TP from large to small in turn was C>B>D>A; According to ANOVA, the TN, NH4-N, TP, and CODMn in the experimental group were significantly lower than those in the blank group(p﹤0.05);In the removal of TN, the experimental group C was significantly different with A and D(p﹤0.05); In the removal of TP, the experimental group C was significantly different with A,B and D(p﹤0.05), so the best biomass ratio of modular Vallisneria natans and Elodea nuttallii was 864 g/m2:432 g/m2. |
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