| Lake Eutrophication has become the major problem facing with worldwide water environmental researchers, the research on eutrophication mechanism of natural lake has never stopped. This paper mainly studied on the relationship between algae and nitrifying bacteria to illustrate the mechanism of lake eutrophication.1. The main findings of the research as follows:(1).Ziyang lake:Ecological system remains a basic balance after a long-time control, the water quality indicators maintained in classâ…£, even in the highest-temperature month(July and August), chlorophyll concentration was low and algae bloom would not happen, the level of NH4+-N and NO3--N began climbing up when entered into winter, while in summer NO3--N was absence. The result of Real time PCR showed that the quantity of AOB in Ziyang lake maintained in the lowest level, about 1.82 X 102 CFU/mL, until September, the units of AOB(ammonia oxidizing bacteria) increased by ten times, to 9.9 X 103CFU/mL,in addition, Nitrobacter increased in the later month. However, from January, due to the temperature dropped, the numbers of each bacteria began to decrease, the population change of nitrobacteria could be the possible reason of the NH4+-N and NO3--N accumulation in winter.(2).Shuiguo lake:arm of Donghu lake, which is minor class V,a severe eutrophication water body. The content of NH4+-N remained a high level as an average of 5.44 mg/L and when entered into June, the concentration of chlorophyll-a soared up, outbreak of algae bloom in Lake Shuiguo was reported. In this period, the level of NH4+-N concentration greatly descend, maintained in 1 mg/L-2 mg/L, and the result of Real time PCR showed that AOB and Nitrobacter both decreased in this period, the amount of this two bacteria were both the minimum in all months, until middle August, the number increased to 105 and 107 unit/ml respectively.(3).Lingjiao lake:hydrophytes were overgrowth, which lead to serious inner pollution, and water bloom broke out in the later summer. As Ziyang lake,NH4+-N grew from 0.32 mg/L to 1.90 mg/L suddenly in November, NO3--N increased to the peak value 0.39 mg/L in January. While in June, NO3--N concentration was lowest for the whole years, and it was same as the last years. From the negative relativity between chlorophyll-a and quantification results, it is reasonable that each bacteria decreased in June when algaes vigorously grew, while in October, nitrobacteria clearly began to reproduce. In conclusion, the three lakes showed the characteristics that algae inhibits nitrification.2. Laboratory microcosms results showed that:in natural coexistence system, when in illuminated condition, NH4+-N rapidly reduced from 5.52mg/L to 0 in only 6 days, and NO2--N, NO3--N didn't accumulate; when in dark condition, NH4+-N reduced gradually and NO2--N rose up at the same time, from 0.04 mg/L to3.89mg/L.In pure culture coexistence system, when in illuminated condition, NH4+-N dropped from 30mg/L to 7mg/L in 20 days, and the other N indicator remained the original concentration, when in dark condition, NH4+-N didn't change a little in the first 13 days. but after 17days, NH4+-N dropped as NO2--N raised up from 0 to 14 mg/L, and then NO2--N was transformed to NO3--N totally on the 27th day. Accordingly, regardless of the natural or pure culture coexistence system, in the light, algae growth inhibits nitrification, while in the dark, nitrobacteria had good activity and nitrogen transform rates.The population of nitrobacteria and the water quality indicators illustrated that:the growing of algae inhibits the reproducing of nitrobacteria, and the same results was deduced from the microcosms experiments. Consequently, the hypothesis reason of coherent rules in natural lakes was valid, and the result provided the theoretical basis of some technical problems in the process of polluted lakes treatment. |
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