| With the progress of industrial and agricultural technology and the rapid development of urbanization, more and more domestic sewage, industrial and agricultural wastewater were discharged into the environment, leading to water quality deterioration yearly, and water pollution becomes a particularly serious problem. Water is the first factor of the survival of mankind, so water quality deterioration directly harms to people’s health. Water quality is evaluated by detecting all kinds of pollutant and its change of concentration in water, which can provide a technical support for pollution control. Dissolved oxygen(DO) is the basic guarantee of normal metabolism of various aerobic aquatic organisms, and is also an important indicator of water body self-purification, at the same time, it is served as top priority of daily and emergency monitoring.Based on simulated experiment, through membrane electrode method, this paper aimed to study diurnal variation of DO in water in different factors by controlling algae density,temperature, sediment and biomass respectively. By linear regression analysis, we hope to find out the correlation between the factors and the dissolved oxygen, and calculated quantitative relationship between each factor and DO in certain range, and then explore the effect of each factor on change of DO in water.As an important primary producer of water, the growth and metabolism of algae is very sensitive to the change of dissolved oxygen in water. Algae released oxygen by photosynthesis at day(DO increase) and consumed oxygen at night(DO decrease), resulting in greater DO difference in water between day and night. DO in water varied regularly with change of light intensity, that is to say, with the increase of light intensity, the photosynthesis of algae enhanced and produced more oxygen, and light intensity reached maximum at a moment in the afternoon,when DO in water also reached maximum; on the contrary, with the decrease of light intensity,DO reduced. When the algae density in the water body is in a certain node, oxygen producing by photosynthesis and oxygen consuming by respiration will reach dynamic equilibrium, and the DO diurnal variation of the water body is not significant, which is basically maintained, at a certain level.Aquatic organisms consume oxygen in water to achieve metabolism(such as respiration,motion, maintaining body temperature). The results indicated that biomass had a significantly negative relationship with DO, and DO values were reduced with increasing biomass, when biomass were too much, it would lead to death. By Spearman correlation analysis, the coefficientbetween biomass and DO was r =-0.820(p = 0.001 < 0.05), and linear correlation equation was Y(DO)= 6.310- 0.194X(Biomass)(R2 = 0.793).The effect of water temperature on DO is mainly about solubility of oxygen in water. The results showed that water temperature and dissolved oxygen were significantly linearly negatively correlated, and DO values were raised with the drop of water temperature. By Spearman correlation analysis, the coefficient between temperature and DO was r =-0.690(p =0.013 < 0.05), and linear correlation equation was Y(DO) = 10.745- 0.204X(Temp)(R2 = 0.648).Microorganisms and organic matter in the sediment are the main factors of oxygen consumption in water. Theoretically, with the increase of the sediment, the more dissolved oxygen are consumed in water, however in the experiment, condition was not so. Adding sediment into water by three groups, result showed that all do values were decreased, but groups with less sediment were consumed more oxygen than more ones. Reason was that with sediment’s increase, water was in anaerobic environment and oxygen consumption rate was reduced. |
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