Studies On The Impact Of External Carbon Source On Growth Of Microcystis Aeruginosa And Quality Of Aquaculture Water

The problems of eutrophication of rivers and lakes are more serious than before with fast development of agriculture & industry and production and discharge of large amount of organic waste, and the water-bloom threatens not only the development and utilization of water resources, but also the health of human and animal.In recent years, the removal and controlling methods of blue-green algae bloom mainly include:killing them chemically, removing them technologically, inhibiting or eating them by plant allelopathy and so on. Although each method has achieved some results, but there are some limitations. In order to better governance blue-green algae bloom, scholars carried out detailed research and discussion on the bloom outbreak mechanism in the world, and they put forward many theories and hypotheses.Now the mechanism study of environmental factors on large-scale outbreak of algae has been a hot topic in academic. Although the reasons for the algae blooms could be attributed to the external environment factors, such as illumination, temperature, hydrological and meteorological conditions, the excess nitrogen and phosphorus and so on, however, it is not the only causing factor. Many algae are not strictly autotrophic growth, for example, the Microcystis not only has the characteristics of plant to carry out photosynthesis autotrophic growth, but also has some bacteria characteristics to take advantage of external carbon source for polyculture growth.With light and organic as the energy source, the algae cells can absorb and utilize the organic carbon and inorganic carbon to synthetize itself the energy material at the same time. Considering the mixotrophy property of algae cells applied in the practice of cultivating some economical algae, we can suspect that this mixotrophy mechanism of algae and water bloom outbreak has some relationship. And from the current research concerning the effect of organic carbon on algae growth, we could find that the exogenous organic carbon makes a different effect on the algae in different physical and chemical and nutrient conditions. Therefore, it is very necessary for human to further study the relationship between exogenous organic carbon and algae growth, which has a big significance for a better understanding of the mechanism of water bloom and control the bloom outbreak.The type of water bloom in China is mainly blue-green algae, and the preponderant alga of the Cyanophyta is the Microcystis, the dominant specie of the Microcystis is the Microcystis aeruginosa. Therefore, this article chooses the Microcystis aeruginosa as the research object, by discussing the impact of the light, temperature and concentration of exogenous organic carbon on the growth of the Microcystis aeruginosa, and thus providing some scientific basis for further understanding of the mechanism of water bloom.In addition, with the rapid development of aquaculture, and the increasing scale farming and breeding density, however, the potential environmental pollution problems are getting worse and worse. In order to improve the water environment, reduce the amount of feed delivery and probability of occurrence of fish disease, the bio-flocs technology is widely used in aquaculture. This technology could purify the water by adding organic carbon, then regulating the carbon and nitrogen ratio in water, thereby promoting the growth of heterotrophic bacteria and then absorbing and transforming the water pollutants. As the water nutritional level has reduced, and the heterotrophic bacteria multiplied, which inhibited the growth of algae bloom and then reduced the probability of occurrence of water bloom. In order to verify the relationship between this technology and the growth of algae, this topic chose the water which has low-density fish and low water exchange as the research object, after adding organic carbon into it, researched on the impact of organic carbon on the water quality by measuring the content of chlorophyll a and water quality index. Thereby this research provides not only a new way of thinking for further study of the mechanism of water bloom, but also a new reference for the special aquaculture water the growth of algae.Experimental results were as follows:1. Under suitable conditions, low concentrations of glucose and fermentable carbon source could promote growth of Microcystis aeruginosa. Glucose concentration promoted most when its concentration was 30 mg/L, the result was close between glucose and fermentable carbon source. Both of two organic carbons significantly inhibited growth of Microcystis aeruginosa.2. The most suitable light intensity of Microcystis aeruginosa was between 30001ux and 60001ux. Low and high light intensity would inhibit growth of algae cells, Microcystis aeruginosa had a strong ability to adapt low and high light intensity when organic carbon added, the biomass of Microcystis continued to increase under the light intensity of 5001ux. Under the light intensity of 60001ux Microcystis aeruginosa grew fast after being inhibited, its biomass exceeded the 30001ux group at last.3. The most suitable temperature of Microcystis aeruginosa was 30℃. Hypothermia was significantly inhibited growth of Microcystis aeruginosa, the number of algal cells continued to reduce in the condition of polyculture.However, Microcystis aernginosa had a strong tolerance of high temperature (40℃), in 15th day of the experiment, its cell abundance was greater than the temperature of 25℃4. In simple sterile medium environment, the reaction rate of glucose and Microcystis aeruginosa was faster than that of fermentable carbon source and Microcystis aeruginosa. There were not significant differences of biomass under the treatment of two different organic carbon sources.5. There was an obvious inhibitory effect on the growth of chlorophyll a content after adding organic carbon source into the water. Due to the mixotrophy property of algae cells, at the beginning of adding glucose and fermentable carbon source into the experimental group, the content of chlorophyll a increased faster than the control group CK. After adding glucose as the organic carbon source into the experimental group, the content of ammonia-nitrogen and total nitrogen fell in the early, and rose in the late.6. There was an obvious inhibitory effect on the growth of ammonia-nitrogen and COD content after adding organic carbon source into the water. And the inhibition of glucose on COD is greater than the inhibition of organic carbon, the removal effect of organic carbon on ammonia-nitrogen is greater than the effect of glucose.7. The content of COD, ammonia-nitrogen, total nitrogen and total phosphorus in the experimental group with organic carbon source all has decreased inordinately during the training.8. The number of the culturable bacteria in experimental group with organic carbon source increased significantly.9. Adding organic carbon could significantly improve water quality and reduce total biomass of water algae.