长江口营养盐结构特征及其对浮游植物的限制

Structure characteristics of nutrients and their restrictive effect on phytoplankton in the Yangtze River Estuary

根据2013年5月、11月两个航次的调查资料,分析了长江口营养盐浓度及其结构的分布变化,并探讨了营养盐对浮游植物的限制情况。长江口营养盐分布存在季节差异:口门外NO3-N、NO2-N浓度均为春季高秋季低,PO34-P、3SiO2-Si、NH4-N浓度则秋季高春季低,口门内除NO2-N外,NO3-N、PO34-P、SiO23-Si、NH4-N浓度均为秋季高于春季。NO3-N、PO34-P、SiO23-Si浓度从近岸向外海逐渐降低,NO2-N、NH4-N浓度分布规律不明显。NO3-N是DIN的主要存在形态,其占DIN的比例为春季95%、秋季83%。春季、秋季DIN/P均高于16,表现出长江口过量的DIN输入,春季Si/DIN基本小于1,秋季Si/DIN大于1。春季由于硅藻的局部生长使DIN/P异常升高、Si/DIN异常降低,秋季西北部海区受苏北沿岸流影响,呈低DIN/P值和高Si/DIN值分布。受含过量DIN、SiO23-Si的长江冲淡水的影响,春、秋季均表现为PO34-P潜在相对限制。春季由于浮游植物的大量吸收,局部出现PO34-P、SiO23-Si的绝对限制。当同时考虑绝对限制和潜在相对限制时,春季15.38%的站位受PO34-P限制,限制情况较上世纪90年代更为突出。

The concentrations and spatial distribution of nutrients, nutrients structure characteristics and their restrictive effect on phytoplankton in the Yangtze River Estuary and the adjacent East China Sea were studied on the basis of two cruises in May and November. The results showed that the concentrations of NO3^-N and NO2-N were higher in spring and lower in autumn outside the mouth, while PO4^3--P,SiO3^2--Si and NH4^＋ -N have the opposite seasonal distribution. The concentrations of NO3^-N,PO4^3--P, SiO3^2--Si and NH4^＋ -N were higher in autumn than those in spring inside the mouth. The concentrations of NO3^-N, PO4^3--P and SiO3^2--Si decreased from the inshore to the offshore gradually, but the distribution regularity of NO2-N and NH4^＋ -N was not obvious. NO3^-N was the main chemical pattern of DIN and occupied about 95% in spring and 83% in autumn in the water area. The proportion of DIN/P was above 16 in both spring and autumn, indicating the excessive DIN input in the estuary. The ratio of Si/DIN was below 1 in spring and higher than 1 in autumn. Due to the partly bloomed diatom in spring. The DIN/P ratio increased and Si/DIN ratio decreased abnormally. In autumn, affected by Subei Coastal Water, the northwest waters showed low DIN/P values and high Si/DIN distributions. In the investigated waters, the PO4^3--P relative potential nutrients limitation was revealed under the influence of Changjiang Dilution Water with high DIN and SiO3^2--Si both in spring and autumn, while regional PO4^3--P and SiO3^2--Si absolute limitation occurred in spring as a result of massive PO4^3--P and SiO3^2--Si uptake by phytoplankton. When both absolute limitation and relative potential nutrients limitation were considered, 15.38% of the stations presented PO4^3--P limitation which was more serious than that in the 1990＇s.