养殖废水排放对红树林沉积物氧化亚氮通量的影响及机理研究

Mangrove sediments have been recognized as a potential source of nitrous oxide (N2O) gas. Mangrove wetlands also receive the anthropogenic nutrient input, which could greatly enhance the N2O emission from mangrove sediment and contribute to global warming problem. However, the atmospheric N2O flux and the microbial mechanisms involved in the N2O production are still poorly characterized in the mangrove wetlands, especially those under anthropogenic disturbances. Coastal aquaculture is a common human activity adjacent mangrove areas, of which the wastewater is often directly discharge into mangrove wetlands. The present study therefore aims to investigate the effect of discharge of wastewater from aquaculture on the sediment N2O flux and the mechanisms that involved in this effect. We study the long-term effect of wastewater discharge on N2O flux and microbial community, as well as the antibiotic contents in mangrove wetlands, and also the temporal changes in above parameters after a single discharge. Using microcosm experiments, we also study the enhancements of N2O flux by the nutrients in the wastewater and test if antibiotics in the wastewater would pose any inhibition effect on N2O emission from mangrove sediment. How inorganic nitrogen and antibiotic components affect the N2O emission from mangrove sediment are also investigated. The mechanisms are explained by the changes in the compositions of inorganic nitrogen and the microbial genes involved in the N2O production or consumption. Moreover, the roles of recovery of microbe under antibiotic stress and mangrove plant play in sediment N2O emission due to wastewater discharge are also investigated. In addition, the fate of inorganic nitrogen in mangrove sediment is traced using isotope 15N, and on the other hand to quantify the contribution of ammonia or nitrate in N2O emission.

红树林沉积物是氧化亚氮（N2O）的潜在排放源，外源性营养物质的输入将促进红树林沉积物的N2O排放，加剧大气增温效应。但目前关于红树林（特别是人为活动影响下的红树林）沉积物N2O气体排放及其机理的研究仍有限。本项目针对高位养殖池塘的废水排放这一普遍现象，研究其对红树林湿地沉积物N2O释放通量的影响及其机制。项目将研究养殖废水排放对红树林湿地沉积物环境及N2O通量的累积和短期效应；同时开展模拟实验研究营养盐和抗生素污染对红树林沉积物N2O通量及沉积物环境的影响，并从沉积物无机氮组成和参与N2O生产和消耗的微生物的丰度变化两个角度探讨这种影响的机理。本项目也研究红树植物对废水排放的N2O增排效应的作用，并利用同位素标记的手段探讨无机氮在沉积物中的归宿。研究结果有助于进一步认识养殖污染的生态效应和红树林湿地对大气温室效应的贡献，对近岸海洋环境保护和红树林保护具有一定意义。

高位养殖是我国红树林沿岸最常见的生产活动，养殖过程排放的清塘废水携带着大量的营养物质和抗生素等污染物质对红树林沉积物的氮代谢必然产生影响。本项目针对N2O这一具有大气增温效应的氮代谢产物，以福建九龙江口红树林为研究区，探讨养殖清塘废水中营养盐、抗生素和红树植物对红树林沉积物的N2O排放的影响及其潜在机制。研究结果显示，富含氨态氮的清塘废水排入红树林后，刺激了红树林沉积物中N2O排放（可达到>100 µmol m-2 h-1），而小潮日排废产生的增派效应的持续时间长于大潮日，沉物N2O通量与沉积物氨态氮含量和AOB-amoA基因丰度之间的相关性表明微生物硝化作用是沉积物中N2O重要来源。沉积物中抗生素含量的调查发现抗生素污染在红树林区域的污染现状不容乐观。针对九龙江口的典型抗生素，通过模拟实验证实清塘废水中的抗生素能够抑制沉积物中的N2O通量，但N2O通量在短期内均可出现恢复，恢复的程度与时间因抗生素种类和浓度而异，总体上高氮水平下N2O通量的恢复更明显。在此基础上，本项目使用氟苯尼考研究不同氨态氮水平下抗生素对沉积物N2O通量的累积影响，研究结果显示氨态氮可促进抗生素抑制作用下沉积物N2O通量的恢复，高浓度氮水平相比中等浓度作用下N2O通量的恢复更快。此外，红树植物可调节抗生素对N2O通量抑制作用，表现为植物和抗生素联合作用下沉积物N2O的通量高于无抗生素的处理组。本项目的研究结果显示，养殖清塘废水排放红树林后将加剧沉积物的N2O的释放，而清塘废水中抗生素和红树植物可能不会减弱N2O的总排放量。因此在全球气候变化的背景下，我国南部沿岸地区的养殖废水排放对红树林沉积物温室气体排放的作用不容忽视。