珠江口浮游植物叶绿素a和初级生产力的季节变化及其影响因素

摘要

Based onin situ physical and biological data collected in different seasons between 2014 and 2015, we described systematically the spatial-seasonal characteristics of chlorophyll a (Chl a) and primary production (PP) in the Pearl River Estuary (PRE) and their relationships with environmental factors. The results indicated that the average values of Chl a concentration and PP in the PRE were 3.77 mg·m–3and 27.86 mg C·m–3·h–1, respectively. Both were higher in spring than in the other seasons, and the lowest were in winter. The spatial distribution of phytoplankton was mainly driven by the Pearl River discharge and the phytoplankton bloom was related to the location of salinity front. Due to nutrients limitation in the lower parts of the estuary, the bloom occurred in the upper parts when river discharge was relatively small. In contrast, although the nutrients were favorable for phytoplankton growth during wet season with large river discharge, the bloom was absent in the waters near the outlets likely associated with light limitation and dilution. The distribution of primary production in the PRE was well related to Chl a. The results also suggested that phosphorus was the potential limiting factor for phytoplankton growth in the lower parts of the PRE during wet season and low temperature was another reason for low primary production besides light in winter. Compared with previous results, the primary production was in the intermediate level in PRE during 2014~2015. The mean value of carbon assimilation index (AI) in the PRE was 7.51mg C·(mg Chl a)–1·h–1 and the carbon fixation level was 261.52 g C·m–2·y–1.%基于2014—2015年4个季节的现场调查数据,系统阐述了珠江口水域浮游植物叶绿素a和初级生产力的空间分布和季节特征,并结合环境因子进行了分析。结果表明：研究水域表层年平均叶绿素 a 浓度和初级生产力分别为3.77mg·m–3和27.86mg C·m–3·h–1,季节变化均为春季>夏季>秋季>冬季。径流量是珠江口浮游植物空间分布的主要驱动因素,并且浮游植物的旺发与河口盐度锋面的位置密切相关。径流较小的季节,由于珠江口外营养盐浓度较低,叶绿素a浓度高值区出现在内伶仃洋水域；随着径流量的增加,叶绿素a浓度高值区随盐度锋面向珠江口外移动,而口门附近浮游植物生长受光限制和径流稀释影响并未出现高值。初级生产力的空间分布趋势与浮游植物叶绿素a相似,二者之间存在显著的正相关关系。研究还表明：夏季,珠江口外由于浮游植物旺发消耗了大量营养盐,磷酸盐浓度被耗尽使其成为浮游植物生长的限制因子；冬季,光限制和低温可能是造成浮游植物初级生产力较低的原因。与以往研究结果对比,珠江口初级生产力处于中间水平,浮游植物碳同化系数年平均值为7.51mg C·(mg Chl a)–1·h–1,河口固碳水平为261.52g C·m–2·y–1。