曝气复氧对底泥氮素生物地球化学循环影响的作用机制研究

摘要

通过分析底泥氮污染物释放规律和转化过程,以及底泥生境、氮形态变化和氮循环功能微生物群落结构变化的规律,探讨了不同曝气复氧条件影响底泥氮生物地球化学循环的生物代谢、物理化学联合作用的机制.结果表明:曝气复氧对底泥中氮的生物地球化学循环影响是一个包括微生物代谢作用和物理化学作用的复杂联合作用过程.水体好氧环境的改变主要引起参与底泥氮循环的硝化、亚硝化和反硝化功能菌群群落结构的演变,对异养菌和氨化菌的影响不大,证明环境好氧条件的改变对底泥有机质生物分解产生氨氮的微生物代谢过程影响不大,主要对底泥释放的氨氮硝化、反硝化等生物转化过程产生大的影响.不同溶解氧条件下,底泥释放的氮素在微生物作用下主要以NH4+-N和NO3-N的形式进入试验体系,并在特定的氧化还原电位(临界值-200 mV)和pH(临界值6.70)条件下通过物理化学作用在底泥中以离子交换态氮(IEF-N)、碳酸盐结合态氮(CF-N)、铁锰氧化态氮(IMOF-N)及有机态和硫化物结合态氮(OSF-N)等不同形态氮相互转化,同时,在氮的转化和循环过程中部分输入上覆水体.在低溶解氧组实验条件下[ρ(DO)＜0.5 mg·L-1],底泥向水体输出氮总量为底泥可转化态氮的19.7％,主要为氨氮,最大释放速率达到289.13 mg·m-2·d-1,释放的质量浓度可达到18.8 mg·L-1;好氧条件下(DO饱和),底泥向水体输出氮总量为底泥可转化态氮的1.8％；好氧-缺氧条件下为11.7％,主要以N2的形式释出系统.%Based on the analysis of the releasing and conversion process of nitrogen pollutants, the ecological habitat and nitrogen forms changes in sediments, and the transformation of microbial community structure in different aeration conditions, the biological and physicochemical combined impact mechanism of different aeration level on biogeochemical cycling of nitrogen in sediments was studied. The results showed that the effect of aeration on biogeochemical cycling of nitrogen in sediments was a complicated process that contains microbial metabolism and physic-chemical reaction. The change of DO concentration in the upper water mainly caused the evolution of microbial community structure including nitrifying bacteria, nitrosobacteria and denitrifying bacteria that take part in the nitrogen cycling process, while it had little influence on the heterotrophic bacteria and ammonifiers. These proved that microbial metabolism that ammonia nitrogen decomposed by organism from organic matter was not affected by the change of aerobic condition, while the nitration and de-nitrification were greatly affected. With different aeration conditions, the ammonia nitrogen released by sediments was imported to the experimental system in the form of NH4+N and NO3--N. Through the physicochemical reaction, they transformed mutually among ion-exchangeable form (IEF-N), carbonate form (CF-N), iron-manganese oxides form (IMOF-N) and organic-sulfide form (OSF-N) in sediments with a specific ORP (critical value -200 mV) and pH (critical value 6.70). Meanwhile, different forms of nitrogen were released into upper water during the conversion and the cycling process. With a low DO concentration [p(DO)<0.5 mg·L-1], the nitrogen released from sediments to upper water in the form of ammonia nitrogen accounted for 19.7% of transferable nitrogen , and the maximum releasing rate and the maximum releasing concentration were up to 289.13 mg·m-2·d-1and 18.8 mg·L-1 respectively. With an aerobic-anaerobic condition, the nitrogen released into the atmosphere in the form of N2 accounted for 11.7% of transferable nitrogen, and 1.8% with a saturated DO condition.