Nutrient distribution and its relationship with occurrence of red tide in coastal area of East China Sea
东海近海海域营养盐分布特征及其与赤潮发生关系的初步研究

Nutrient (NO 3 --N, PO 4 3--P, SiO 3 2--Si, NH 4 +-N,etc.) concentrations in coastal area of East China Sea were measured during April 25 to May 2, 2002,and the relationship between the spatial distribution of the nutrients and the red tide occurrence in the studied area was analyzed. The results showed that compared to the 1 st class seawater quality of the national standard, the concentrations of dissolved inorganic nitrogen (DIN) and PO 4 --P were 46% and 60% higher, respectively, showing that the studied area, especially the Changjiang River estuary and the Hangzhou Bay, was at a disadvantage of eutrophication. Furthermore, the nutrient concentrations inshore were much higher than those offshore,and the isolines nearly paralleled with the coastline, meaning that the nutrient distributions were mainly influenced by terrestrial discharges. It also showed that the relatively high concentrations of nutrients, especially DIN and PO 4 3--P, might result in the red-tide occurrence. However, the red tide did not occur in the area with the highest concentrations of the nutrients, further demonstrating that the eutrophication was not the unique environmental factor inducing red-tide occurrence.