Studies on nitrous oxide from oxidation-reduction boundary layer in brackish lakes

为了解中海微咸湖水中硝化和反硝化作用对氧化亚氮（N_2O）积累的影响，采用培养实验研究了溶解氧（DO）浓度对氧化亚氮（N_2O）积累的影响。随着DO浓度的降低，硝化产氮活性（N_2O_N）显著增加。低DO（10-30%饱和度）诱导高N_2O_N。与硝化作用相比，反硝化作用产生N_2O_D的活性随着DO浓度的降低而降低。在低DO条件下，由于N_2O进一步还原为N_2，反硝化过程中N_2O积累较少。从日本新岛咸淡湖沉积物中分离到两株产n22o细菌：气单胞菌和弧菌。气单胞菌和弧菌的最适生长盐度分别为0 ~ 20 psu和10 ~ 20 psu。这两个菌株都是嗜盐菌，对咸淡水地区有利。研究了H_2S浓度对这些菌株N_2O生成和积累的影响。在h2s浓度为1 ~ 5 mg /L和1 ~ 10 mg /L的条件下，气单胞菌和弧菌的n22o积累活性加快。H_2S是N_2O积累的重要因素。建立了一种用次氯酸盐气相色谱法测定淡水河流和湖泊中羟胺的新方法。用丁基橡胶塞和无顶空铝盖密封盛有样品水的玻璃小瓶，然后通过注射器将次氯酸钠溶液注入小瓶中，使羟胺转化为氧化亚氮。用气密注射器用99.9%的氮气制备玻璃小瓶的头部空间。用带电子捕获检测器的气相色谱仪测量气相氧化亚氮。根据溶解度公式计算了液相中溶解的氧化亚氮。少

In order to understand the role of nitrification and denitrification in the accumulation of nitrous oxide (N_2O) in the hypolimnetic water of brackish Lake Nakaumi, the effects of dissolved oxygen (DO) concentration on these activities were investigated by incubation experiments. N_2O-producing activity by nitrification (N_2O_N) increased markedly with decreasing concentration of DO. Low DO (10-30% saturation) induced high N_2O_N. In contrast to nitrification, N_2O-producing activity by denitrification (N_2O_D) decreased with decreasing concentration of DO. Little N_2O was accumulated during denitrification under low-level conditions of DO, because of further reduction of N_2O to N_2.Two strains of N_2O-producing bacteria, Aeromonas sp.and Vibrio sp.were isolated from the sediment in brackish Lake Shinj, Japan. The optimum salinities for growth of Aeromonas sp.and Vibrio sp.were 0-20 and 10-20 psu, respectively. Both strains were halophile favorable for brackish water areas. The effect … More s of H_2S on the production and accumulation of N_2O by these strains were studied. N_2O-accumulating activities by Aeromonas sp.and Vibrio sp.were accelerated at 1-5 mgS/L and 1-10 mgS/L of H_2S concentrations, respectively. H_2S was an important factor for N_2O accumulation.A new and simple method for the determination of hydroxylamine in environmental water, such as fresh rivers and lakes using hypochlorite, followed by its gas chromatographic detection, has been developed. A glass vial filled with sample water was sealed by a butyl-rubber stopper and aluminum cap without head-space, and then sodium hypochlorite solution was injected into the vial through a syringe to convert hydroxylamine to nitrous oxide. The head-space in the glass vial was prepared with 99.9% grade N_2 using a gas-tight syringe. The nitrous oxide in the gas-phase was measured by a gas chromatograph with an electron-capture detector. The dissolved nitrous oxide in the liquid-phase was calculated according to the solubility formula. Less