Effect Of Outbreak And Extinction Of Algal Blooms On Biological Properties Of Sediment In Lake Chaohu

In recent years, algae bloom attracts more and more attention due to its negative effects on aquatic ecosystem of lake. Outbreak and extinction of algal blooms not only influences water physical and chemical properties, but also affects sediment properties. These changes of physical and chemical properties of water and sediment may affect microbial activity, microbial community structure and enzymes activities in sediment. It is well known that microbes and enzyme have great impact on the transformation and transportation of pollutants and the cycle of mineral elements such as nitrogen and phosphorus in sediment. Therefore, it is significant to study effect of outbreak and extinction of algal blooms on biological properties of sediment. Result will provide information for in-depth undersanding influence of algae bloom on aquatic ecosystem and using sediment microbes to remedy lake eutrophication.In this study, Lake Chaohu was selected to study effect of ourbreak and extinction of algal blooms on biological properties of sediment. According to the historical data, regions with and without algal blooms as well as formation time of algal blooms werr determined. Eight times of water and sediment sampling were taken from May15to September19. Biomass of microbes with special function, microbial community structure, enzyme activity, sediment and water properties were determined respectively in laboratory. The main results are as follows:(1) In region with algae bloom, algae began to grow in mid-May, and algae bloom formation completed in June20. The extinction of algae bloom occurred after September5. In region without algae bloom, algal concentration slightly fluctuated during this perios. Algae bloom had great impact on the physical and chemical properties of water and sediment, such as decreased water transparency (SD) and dissolved oxygen(DO), increased contents of TN, TP and TOC. In region without algae bloom, however, above parameters showed little variation during this period.(2) Biomass of microbes with special function (such as nitrate bacteria, nitrate-reducing bacteria, nitrite bacteria, nitrite-reducing bacteria, organic phosphorus solubilizing bacteria, inorganic phosphate solubilizing bacteria, sulfate bacteria, sulfate-reducing bacteria, iron-reducing bacteria) greatly shifted in the outbreak and extinction of algal blooms. In algae bloom lasting stage, aerobic microbial biomass (such as nitrate bacteria, nitrite bacteria and sulfate bacteria) was significantly lower than these in the formation and extinction of algal blooms, while anaerobic microbial biomass (such as nitrate-reducing bacteria, nitrite-reducing bacteria and sulfate-reducing bacteria) was significantly higher than these in the formation and extinction of algal blooms. In region without algal blooms, biomass of above microbes changed slightly during these stages. In addition, microbial biomass in region with algal blooms was generally higher than that in regions without algal blooms. Above variations may be due to the changes of the physical and chemical properties of sediment (such as DO, pH, TOC, and so on) caused by algae bloom.(3) In region with algae bloom, PCR-DGGE analysis showed that microbial community structure in sediment significantly shifted in the outbreak and extinction of algal blooms. Microbial diversities in May and September were much lower than those in June, July and August, and those may be related to the algae bloom and temperature variation. Compare with region without algae bloom, microlbial diversities in region with algae bloom in May and June were lower, while were higher in July and August. However, the difference in microbial diverty between regions with and without algae bloom was slight in September. Microbial diversity in region without algae bloom also showed shift during this stage, and the possible reason may be related to the temperature variation.(4) In region with algae bloom, enzyme activity in sediment shifted greatly in the outbreak and extinction of algal blooms. Urease activity decreased befor August1with time, and then significantly increased. Alkaline phosphatase activity was low between June20and August1, and then significantly increased. Catalase activity increased at first and then decreased with time; polyphenol oxidase activity generally showed downward trend with time. Enzyme activity in region without algae bloom also showed variaty with time, which may be related to the variation of envitonmental temperature and TOC concentration.In summary, the outbreak and extinction of algal blooms in Lake Chaohu greatly impacted microbial characteristics of sediment, which may be related to the variaties of DO, ORP, TOC, pH, and nitrogen and phosphorus concentrations caused by algae bloom.