长江口水域富营养化特性的探索性数据分析

Exploratory Data Analysis to the Study of Eutrophication in the Yangtze River Estuary,China

根据2004年2、5、81、1月长江口及邻近海域的调查结果,选择8个与富营养化有关的特征参数,包括营养盐浓度(NO3-、NH4+、PO43-、TN、TP)、化学耗氧量、叶绿素a浓度和浮游植物细胞丰度等,应用探索性数据分析方法对该海域富营养化特性进行研究.主成分分析表明,主成分1主要反映氮营养盐和有机污染状况;主成分2反映浮游植物生物量;主成分3体现磷营养盐特点.主成分1从口门内到口门外存在降低的趋势,表明氮营养盐和有机污染主要来源于长江输入.受人类排污影响,主成分1在吴淞口、石洞口和白龙港排污口附近最高.冬季口门内各站位的氮营养盐和有机污染最为严重.春夏季的3个主成分均高于秋冬季,因此春夏季富营养化更为严重.主成分1与盐度之间在秋冬季具有较好的线性关系,在一定程度上可根据盐度预测长江口海域各站位的主成分1,即氮营养盐和有机污染状况.硝酸盐、总氮、总磷和浮游植物细胞丰度等是控制长江口水域富营养化水平时空变化的主要驱动因素.

Four cruises were carried out in the Yangtze River Estuary and its adjacent area in February, May, August and November 2004. 8 variables including NO3^-、NH4^＋、PO4^3-, TN, TP, COD, Chl-a and cell abundance of phytoplankton were analyzed with exploratory data analysis. Three principal components （PCs） are extracted with principal component analysis： N nutrients and COD for PC1, Chl-a and cell abundance for PC2 and P nutrients for PC3. A west-east decreasing gradient in the PC1 indicates N nutrients and organic pollution originate from Yangtze River. Influenced by anthropogenic sewage, PC1 near Wusongkou, Shidongkou and Bailonggang outlets is higher than other stations. N nutrients and organic pollution in stations of inner gate in winter are most serious. PC1, PC2, PC3 in spring and summer are higher so eutrophication level in spring and summer is more serious than other seasons. A good linear relationship between PC1 and salinity exists especially in autumn and winter so N nutrients and organic pollution are predicted to a good extend on the basis of a linear model in which salinity is the independent variable. NO3^- , TN, TP and phytoplankton cell abundance are dominating factors in assessing the variation of eutrophication in the Yangtze Estuary and its adjacent area.