Denitrifiers And Their Denitrification In Eutrophic Lake Sediment

Lake sediments' denitrification is the most important path for the removal of nitrogen from lake. Little research had been carried out on lake denitrification, especially on denitrifiers in aquatic and sedimental environment. The thesis tries to explore the better methods in denitrification in lake sediments.The content of the thesis was divided in two fields: 1) the determination of sediment denitrification and the denitrifiers; 2) nitrate removal from water by denitrifiers. Three profiles on denitrification was carried out for different object studied, included in situ denitrification in lake, sediment samples' denitrification and dominant denitrifiers' denitrification in laboratory.1. The determination of in situ denitrificationThe thesis determined the in situ denitrification in Lake MoChou using acetylene inhibition technique (AIT) during winter and autumn. Result shows AIT method is suitable to determine in situ denitrification of lake sediments. In conditions without the addition of nitrate, the denitrification of sediment in autumn is I4.65 g.m-2,h-1, while it's 6.25 g.m-2.h-1 at lest in winter. In condition with nitrate addition, sediment denitrification is 78.44 g.m-2.h-1 in autumn.2. The distribution and involving functions of denitrification in verticalsedimentsIn order to clarify the actual distribution of denitrification in vertical sediment and the functions involved in denitrification ,vertical sediment cores were sampled to study. Results show that denitrification exists mainly within 8cm depth with a denitrification range of 0.08~0.12 mol.L-1.h-1.g-1. The biggest value of denitrification takes place in the depth of 6cm. The analysis of sediment component and corresponding denitrification in different depth shows a positive correlation between organic carbon content and denitrification, alsoa negative correlation between ammonium content in pore water and denitrification. Incubation of sediment under different conditions shows that: sediment has the highest denitrification rate with pH6~7; fermentative carbon such as, glucose, glycerol, sucrose greatly increased sediment denitrification in initial time of incubation. While non-fermentative carbon, e.g., acetate, fumarate, citrate, etc., could not accelerate denitrification during short incubation time (24h), but great denitrification rate took place when incubation time prolonged. Lactate influenced sediment denitrification to a small extent.3. The isolation of denitrifiers and their denitrification abilitiesIn order to screen strains which actually carry out denitrification process, three different methods were employed, e.g., direct dilution method, tartaric acid incubation method and chemostat incubation method. With these methods, representative strains were isolated and identified . The most amount of nitrate reducing micro-organisms in sediment collected in winter season identified as Vibro spp., which did not have denitrification ability except showing the ability of nitrate reducing to nitrite. The dominant strains in chemostat of the samples collected in winter was identified as Pseudomonas alcaligenes, which exhibit great denitrification ability. In summer sediment the dominant strains was the same as the representative strains of which isolated from chemostat incubation, i.e., Paracoccus denitrificans. The strain could carry out a complete denitrification. A strain identified as Pseudomonas aeruginosa was also screened by tartrate incubation method, in which only N2O was found as denitrification production.Due to seldom study has been carried out in the isolation of denitrifiers by using chemostat in sediment , an experiment was done to verify the reliability of the method of chemostat The results showed there was a process of competition among dominant strains isolated by different methods. Chemostat was employed in the competition experiment between two strains in which one is isolated by chemostat , the other by other method. Results showed that the dominant strains isolated by chemostat always exceeded the other...