| Summary: | 博士 === 國立海洋大學 === 水產養殖學系 === 87 === 英文摘要Fates of two antibiotics, chloramphenicol (CM) and oxytetracycline (OTC), in aquaculture pond sediments and effects of these two antibiotics on the nitrogen cycles in the sediments were studied. First, transformation processes of CM and OTC in sediments collected from a freshwater eel pond and a marine shrimp pond were investigated. Then, effects of salinities, temperatures and light intensities on the transformation processes were also elucidated. Finally, effects of CM and OTC on potential nitrification and denitrification in the two types of sediment were investigated. The sorption rates of CM in both types of sediment, 3%, were lower than those of OTC, 95%. CM (60 mg/L) was transformed within 4 days in the sediment slurries (10%, wt/vol) when incubated under anaerobic conditions, and within 12 days under aerobic conditions. The transformation became slower as CM was repeatedly amended into the aerobic sediment slurries. OTC (60 mg/L) was not transformed after incubation for 70 days in the sediment slurries under anaerobic conditions. However, OTC was transformed to undetectable levels within 47 days when incubation proceeded under aerobic conditions. The sorption of CM in the sediments under both aerobic and anaerobic conditions was not affected by treatments of salinities, temperatures and light intensities. Transformation of CM in freshwater sediment decreased with increased salinities under both aerobic and anaerobic conditions. Furthermore, the transformation of CM in the marine sediments under aerobic conditions also decreased with increasing salinities. However, no difference in transformation of CM was found among the various salinities in the marine sediment under anaerobic conditions. Sorption of OTC in the freshwater sediments decreased with increasing salinities. In the aerobic freshwater sediments, the transformation of OTC was lower with no NaCl added (salinity, 0 ppt) than with NaCl added (salinities, 12 ppt, 2.4 ppt and 3.6 ppt). No significant difference of the sorption or transformation of OTC in the marine sediments was found among various salinities. Transformation of CM was faster under 32 C than under lower temperatures, 8 C、16 C and 24 C. In the freshwater sediment, transformation of CM was more sensitive to the decreasing temperatures under aerobic conditions than under anaerobic conditions. Under aerobic condition, transformation of OTC in freshwater sediments differed only between 16 C and 24 C. However, the transformation of OTC in the aerobic marine sediments increased with temperatures higher than 16 C. Under anaerobic condition, no significant effect of temperature was found on the transformation of OTC in both freshwater and marine sediments. No significant differences in the sorption and transformation of CM and OTC in the two sediment slurries under aerobic or anaerobic conditions were found among various light intensities, respectively. The potential nitrification rates were 3.6 and 3.5 mole N g(dry wt)-1 day-1 for the freshwater and marine sediments, respectively. Although quite close in nitrification rate, the increase of nitrification product, NO3-, started earlier in the freshwater sediment than in the marine sediment. Both CM and OTC amended at 60 mg/L inhibited the potential nitrification process. The potential denitrification rates were 9.4 and 5.3 micromole N g(dry wt)-1 day-1 for the freshwater and marine sediments, respectively. The increase of denitrification product, N2O, began earlier in the freshwater sediments than in the marine sediments. In freshwater sediment, both CM and OTC enhanced denitrification rates. However, in marine sediment, CM depressed the denitrification rate to 0.2 micromole N g(dry wt)-1 day-1, which was much lower than when OTC was added.
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