典型滨海湿地沉积物反硝化与硝态氮氨化 相对重要性研究

为揭示典型滨海湿地沉积物中硝态氮还原特征与规律,以长江入海口崇明东滩湿地为对象,采集不同季节和植被条件下(芦苇、互花米草、互花米草-芦苇混合区与光滩)沉积物,借助¹⁵N同位素稀释技术,测定反硝化(Den)与硝态氮氨化(DNRA)速率的变化,探讨两者的相对重要性特征。结果表明:①冬季,互花米草群落沉积物Den速率达31.29 μg/(kg·h),显著高于其他植物群落及光滩(P<0.05),但其在春、夏、秋季最低,仅为2.35～3.36 μg/(kg·h)。表明,冬季可能是互花米草群落沉积物氮素Den逸失高峰期。②春、冬季节光滩带沉积物DNRA速率(>120 μg/(kg·h))明显高于有植被沉积物(<80 μg/(kg·h))。然而,从不同植物群落看来,互花米草群落DNRA速率显著高于其他植物群落及光滩(P<0.05)。相比较而言,夏、秋季节光滩带沉积物DNRA速率显著低于其他植物群落,但其他3个植物群落之间并没有显著差异。表明,春、冬季节互花米草群落更有利于沉积物NO^-₃的氨化。③春、夏、秋3个季节,互花米草群落沉积物DNRA与Den速率的比值(17～29)显著高于其他植物群落(1～14),然而,其在冬季显著低于其他植物群落(P<0.05)。显然,DNRA过程主导着滨海湿地沉积物中NO^-₃的还原。就植物调控策略而言,减控互花米草有助于湿地富营养化和N₂O排放的控制。

The relative importance of dissimilatory nitrate reduction to ammonium and denitrification in sediments in a typical coastal wetland

This study aims to investigate nitrate reduction in sediments in a typical coastal wetland. Sediment samples were taken in different season and in different vegetation conditions(Phragmites australis, Spartina alterniflora community, the intergrowth area of the two species and mudflat)in Chongming Dongtan wetland in the Yangtze River Delta of China. Rates of dissimilatory nitrate reduction to ammonium(DNRA)and denitrification(Den)were estimated using ¹⁵N isotope dilution technique to detect the relative importance of the two reduction processes. Results showed that: ① Den rates in Spartina alterniflora community arrived to 31.29 μg/(kg·h)in winter, which was the highest among four vegetation communities(P<0.05). In contrast, this rates decreased to a very low range of 2.35-3.36 μg/(kg·h)in other three seasons. It revealed that there was a potential high amount of N loss via Den in winter in Spartina alterniflora community. ② DNRA rates in the mudflat(>120 μg/(kg·h))were much higher than those observed in vegetation community(<80 μg/(kg·h))in spring and winter. For different vegetations, the rate in Spartina alterniflora community was the highest(P<0.05). In contrast, DNRA rates in sediments without vegetation were lower than those with vegetation in summer and autumn, and no significant difference among three communities was found. This suggested that Spartina alterniflora possibly facilitates DNRA in spring and winter. ③ The ratios of DNRA and Den in Spartina alterniflora community(17-29)were much higher than those in the other vegetations(1-14)in spring, summer and autumn. However, in winter, this ratios were lower than the others(P<0.05). Therefore, DNRA dominates the reduction of nitrate in the coastal wetland. It would be very necessary to control of eutrification and N₂O emission to reduce Spartina alterniflora in a coastal wetland. It is effective to control eutripication and to reduce N₂O emission via reducing S. alterniflora in coastal metlands.