长江口及邻近海域营养盐四季分布特征

摘要

利用2006年夏、冬季,2007年春、秋季四个航次营养盐调查数据,分析了硝酸盐(NO3)、亚硝酸盐(NO2-)、铵盐(NH4+)、活性磷酸盐(PO43-)和活性硅酸盐(SiO32-)四季大面及典型断面(M1、M4、O6断面)分布特征.结果表明:营养盐大面基本呈西高东低分布趋势,NO3-、PO43-和SiO32-,在长江口和杭州湾海区各个季节均呈双舌分布,可见长江冲淡水和外海水不同程度的混合是其分布的主要控制因素.夏季,受长江冲淡水东北转向的影响,营养盐在口门东北部有一个高值水舌扩展,而春、秋和冬季则并无此现象,营养盐基本在长江口门处向东南方向输送.NO2-、NH4+,春、夏和冬季受上海市排污口影响,点源扩散分布现象明显,而秋季NO2-浓度在122.5°E至125°E间有高值区,可能是由于夏季底层有机质降解再生后高浓度营养盐在秋季被逐渐加强的垂直混合作用带至表面所致.冬季,由于黑潮水深入陆架,相同浓度营养盐等值线比夏季更靠近岸.断面分布上,NO3-、PO43-和SiO32-在春季总体上垂直混合为主要控制因素,夏季层化明显,秋季营养盐层化开始被破坏,垂直混合逐渐占优,冬季则呈上下混合均匀态势；而NO2-、NH4+季节变化规律性不强,受排污口污染扩散影响,长江口以北断面(M1)、长江口主断面(M4)近岸均存在不同程度的高值区.%The distribution of nitrate(NO3- ), nitrite (NO2-)、ammonium (NH4+ ) 、phosphate (PO4 )、silicate (SiO32-) recorded during the four cruises(2006 summer and winter, 2007 spring and autumn), indicates that surface nutrients were high in west and low in east, NO3-、PO43- and SiO32- in Changjiang River Estuary and Hangzhou Bay behaved as double tongue pattern in all seasons, which was regulated by Changjiang River dilution water and offshore water mixing. In summer, nutrients expanded northeast at the river mouth due to Changjiang River dilution water turning northeast, while there was no such behavior in other seasons. NO2-and NH4+ was obvious point source diffusion effected by Shanghai City sewage outfall. The high value area of NO2- at 122. 5°E to 125°E in autumn was caused by high concentration nutrients that regenerated from bottom organic matter and brought to the surface through vertical mixing. In winter, the nutrients contour was closer to coast than that in summer due to Kuroshio water invasion into the shelf. Section distribution of NO3- ,PO43-and SiO32- was mainly controlled by vertical mixing in spring, while the seawater stratification was obvious in summer, which began to be broken up in autumn, and vertical mixing turned to be dominated. In winter, the nutrients distribution was almost uniform from surface to bottom. NO2- and NH4+ didn't present fierce seasonal variation like other nutrients. Influenced by the sewage outfall diffusion, the coastal areas of Ml and M4 sections presented high concentration of NO2- and NH4+,