Preliminary Results Concerning Summer-time Denitrification in the Jiulong River Estuary
- 环境生态－已发表论文 
河口反硝化是削减入海河流氮污染的重要途径,为探明地处亚热带的九龙江河口混合区的反硝化作用,于2010年7月开展13个站位的面上调查,利用n2:Ar法和膜进样质谱分析仪(MIMS)直接测定反硝化产物溶解n2浓度,用吹扫捕集-气相色谱法测定溶解n2O浓度,并估算二者净增量和水气交换通量.结果表明,溶解n2和n2O净增量有明显的区域变化,从淡水端向海域减少,n2净增量为-9.9~66.8μMOl.l-1,n2O净增量为4.3~31.5 nMOl.l-1;n2O饱和度为170%~562%,平均352%;n2水气通量为-2.9~53.2 MMOl.(M2.d)-1,n2 O水气通量为5.2~23.9μMOl.(M2.d)-1,n2 O通量占总通量的0.03%~1.2%(平均0.25%).温度和营养盐(氮、磷)是影响九龙江河口区反硝化作用的重要因子;淡水端(盐度<0.5)反硝化作用及其空间分布主要受硝酸盐含量控制,海水端溶解n2与n2O的增加主要来自淡水端的输送,并受盐度梯度(混合作用)影响.Denitrification is an important process mitigating nitrogen(N) pollution in aquatic systems.Water samples in 13 sites throughout the Jiulong River Estuary were collected in July,2010 in a preliminary investigation of the denitrification rate in this area.As end-products of denitrification,dissolved N2 was measured by determining N2:Ar ratios using MIMS(HPR-40),while the concentration of nitrous oxide(N2O) dissolved in water was determined by Purge and Trap-Gas Chromatography.The results showed significant spatial variance of net increase of dissolved N2(ranging between-9.9 and 66.8 μmol·L-1) and N2O(ranging between 4.3 and 31.5 nmol·L-1) in the Jiulong River Estuary.The net increase of dissolved N2 and N2O declined gradually from river sites to sea sites.Dissolved N2O was supersaturated by 170%-562%.The air-water fluxes of N2 ranged between-2.9 and 53.2 mmol·(m2·d)-1,and N2O between 5.2 and 23.9 μmol·(m2·d)-1.The N2O yield shared only 0.03%-1.2%(average 0.25%) of total N air-water flux.The results suggested that water temperature and nutrient(N and P) were the key factors influencing denitrification.The denitrification rate is controlled by nitrate level at fresh-water sites with salinity <0.5‰.However,in salty waters,net increase in N2 and N2O mainly originated from denitrification occurring upstream of the estuary,and was dominated by the salinity gradient due to tidal mixing.