夏季长江口无机氮的加入与转移 偏移理论稀释曲线的解释

The relationship between dissolved inorganic nitrogen and fresh-saline water mixing during summer in the Changjiang Estuary and the adjacent East China Sea

利用2006年夏季长江口调查数据分析了长江口海域硝酸盐（NO3-）、亚硝酸盐（NO2-）、铵盐（NH4＋）大面分布,NO3-浓度呈近岸高、外海低的特征,NO2-和NH4＋浓度在上海市排污口位置有高值区并向外扩散。NO3-,NH4＋浓度总体上符合咸淡水混合之稀释效应,与盐度的相关系数（r2）分别为0.815,0.255,呈保守行为,而NO2-浓度与盐度的相关性系数为0.074,呈非保守行为。在确定了淡水端元和咸水端元的基础上,做出理论稀释曲线TDL（theoretical dilution line）,由于上海市污染物的输入,淡水端元NO3-,NO2-,NH4＋浓度不同程度地正偏于TDL,在外海深层水范围内有机颗粒矿化再生亦呈加入态势。对应高溶解氧的盐度羽状峰处,由于真光层初级生产较强,表层NO3-浓度负偏于TDL约1~19μmol/dm3,NO2-,NH4＋浓度也存在不同程度的减小。在长江口最大浑浊带附近,由于高浓度悬浮物吸附NH4＋而呈现明显的迁出机制。外海表层海水三氮营养盐浓度数据点偏离TDL程度较小,但在底层由于来自上层的有机颗粒耗氧分解而再生出营养盐,使NO3-,NO2-,NH4＋浓度数据一般在TDL之上。

The spatial variations in nitrate（NO-3）,nitrite（NO-2） and ammonium（NH＋4） concentrations in the Changjiang Estuary and the adjacent East China Sea were described on the basis of the summer cruise in 2006.NO-3 concentrations decreased along a salinity gradient.Owing to the input of the sewage from Shanghai City NO-2 and NH-4 concentrations were very high（up to 8.64,19.81 μmol/dm3 respectively） in the Changjiang Estuaxy area and decreased seaward.Generally NO-3 and NH＋4 concentrations were significantly correlated with salinity,with the coefficient（r2） of 0.815 and 0.255 respectively,suggesting that these two nutrients behaved nearly conservatively,while NO-2 did not behave conservatively（r2=0.074）.Theoretical dilution line（TDL） was obtained by assuming river and ocean end-members.NO-3,NO-2 and NH＋4 concentrations were above values expected for a conservative mixing relationship with salinity at the freshwater end member due to high nitrogen input from the sewage effluence,and in deep water at the oceanic stations because of the decomposition of the organic matter.In contrast,at the salinity plume with high dissolved oxygen（DO） concentrations,the surface NO-3 concentrations were below values expected for the conservative mixing by 1~19 mol/dm3,as a result of high primary production in the euphotic zone,where NO-2 and NH＋4 concentrations were also negatively deviated to various extents.In waters with the highest turbidity in the Changjiang Estuary,NH＋4 was removed due to the adsorption of suspended matter.Overall,NO-3,NO-2 and NH＋4 concentrations at the surface at the oceanic stations deviated from the TDL to less extent,while their concentrations at the bottom were generally beyond values expected for the TDL because the organic matter from the photic zone decomposed and nutrients regenerated.