珠江磨刀门河口枯季叶绿素a环境因子驱动分析

Environmental Controls of Phytoplankton Chlorophyll-a During the Dry Season in the Modaomen Outlet of the Pearl River Estuary

【目的】分析珠江磨刀门河口浮游植物叶绿素a及其驱动因子的潮周期变化,并揭示叶绿素a的环境影响机制。【方法】基于珠江磨刀门河口2017年枯季(1月13-20日)水文水质多要素同步观测数据,采用主成分分析(PCA)和结构方程模型(SEM)确定浮游植物叶绿素a与多个环境因子的关系并量化各因子的驱动作用。【结果】磨刀门水道浮游植物叶绿素a浓度变化范围为0.77～10.92μg/L,口门处变化为0.70～9.01μg/L,磨刀门河口动力驱动下浮游植物叶绿素a的潮周期差异显著。盐度、含沙量和氮磷营养盐亦随潮汐涨落差异显著,而水温无明显潮周期变化。【结论】外海水团对氮营养盐的稀释混合作用强于磷营养盐,而悬浮泥沙对磷营养盐的吸附作用强于氮营养盐。与氮营养盐相比,溶解态磷相对不足,限制磨刀门河口浮游植物的生长。径流(营养盐、悬沙等为代表)、潮流(盐度为代表)对河口浮游植物的影响机制不同,其中氮磷营养盐和水温起着直接作用,而悬沙和盐度间接影响浮游植物叶绿素a的变化。

【Objective】This study aimed to investigate the tidal changes of phytoplankton chlorophyll a and the associated environmental factors in the Modaomen outlet of the Pearl River estuary, to identify the roles of physicochemical properties, and to determine the phytoplankton driver priority.【Method】Based on the field efforts conducted from 13 th-20 th January, 2017 in the Modaomen outlet of the Pearl River estuary, A principal component analysis(PCA) and structural equation modelling(SEM) were carried out in this study.【Result】Phytoplankton chlorophyll-a concentration varied from 0.77~10.92μg/L at the Guadingjiao station along the Modaomen channel and from 0.70~9.01 μg/L at the Modaomen gateThe chlorophyll range indicated a big difference during a tidal cycle;tidal differences in salinity, suspended sediment and dissolved nutrients were found, while no big difference was shown in water temperature.【Conclusion】The diluting-mixing process from marine waters on nitrogen was stronger than that on phosphorus, while the absorption of suspended sediment on the nutrients was reverse. Compared with dissolved nitrogen, the relative deficiency of dissolved phosphorus limited the phytoplankton growth. Different roles of water discharge(represented by nutrients and suspended sediment) and tidal current(represented by salinity) on phytoplankton chlorophyll-a were discovered. In which, various dissolved nutrients directly influenced the phytoplankton, while suspended sediment and salinity played indirect roles.