长江口及其邻近水域叶绿素a的垂直格局及成因初析

 根据2005年9月～2006年5月逐季进行的4次多学科综合调查, 报道了长江口及其邻近水域叶绿素a的垂直分布特征, 并探讨了环境因子和长江冲淡水过程对浮游植物生物量垂直分布的影响。结果表明, 水柱平均叶绿素a在春季最高、冬季最低, 高值区位置因季节而异, 常出现在低盐或等盐线密集的水域; 河口区和外海区水体垂向混合均匀, 除夏季外叶绿素a的垂直变化均较小; 冲淡水区水体呈现层化特征, 叶绿素a高值集中分布在浅层水体。低盐的长江冲淡水占据上层水体, 良好的营养盐条件促进了浮游植物的生长; 外海高盐水控制的下层水体, 较低的营养盐浓度和较弱的光强不利于浮游植物生物量的积累。

VERTICAL PATTERN OF CHLOROPHYLL A IN THE YANGTZE RIVER ESTUARY AND ITS ADJACENT WATERS

Aims The Yangtze River Estuary (YRE) is a complex aquatic system, and large environmental gradients and complicated hydrological conditions make the vertical pattern of chlorophyll a perplexing. Our aims are to 1) describe the vertical profile of chlorophyll a and 2) analyze the environmental factors impacting the vertical pattern. Methods Four seasonal, multidisciplinary cruises were carried out from September 2005 to May 2006 in YRE and its adjacent waters. Chlorophyll a concentration was determined fluorometrically (Parsons et al., 1984) by means of Turner Fluorometry Model 10 (Turner Designs Inc.). Seawater temperature and salinity were measured in situ by YSI 6100 probes (Y. S. I., Inc.). Nitrate, phosphate and silicate were analyzed spectrophotometricly (Valderrama, 1981). Important findings Chlorophyll a concentration was highest in spring and lowest in winter. High chlorophyll a occurred in the low-salinity area or the salinity front. In upper estuary and adjacent sea, chlorophyll a concentration showed slight vertical fluctuations, due to sufficient vertical water exchange. In the plume zone characteristic of water stratification, chlorophyll a was much more concentrated in the upper water column. Skeletonema costatum determined the vertical profile of phytoplankton cell abundance, which correlated well with that of chlorophyll a. Ample nutrients from the water of the Yangtze River stimulated the growth of phytoplankton; nevertheless, low nutrients and weak solar radiation in high-salinity seawater restrained the accumulation of phytoplankton biomass.