珠江口双胞旋沟藻Cochlodinium geminatum赤潮生消过程的环境特征初步分析

Preliminary Environmental Analysis of the Evolution of Cochlodinium geminatum Bloom in the Pearl River Estuary

为了解2009年珠江口双胞旋沟藻赤潮生消过程,探索其生消机制,对赤潮进行了连续10 d（10月28日─11月6日）的跟踪监测,设置了3条监测断面,共12个站位。通过现场测定和实验室分析,研究赤潮藻密度、叶绿素a、营养盐、温度、盐度、p H和溶解氧的变化规律。赤潮区双胞旋沟藻的密度先升高后降低,最高密度达到2.765×107 cells·L-1,叶绿素a含量呈先升后降的趋势,最大值达到172.76μ·L-1,监测海域无机氮和无机磷均处于富营养化水平,无机氮表现出先增加后减少,在赤潮末期稍有回升的趋势,无机磷总体呈现下降趋势。赤潮区水温变化范围为19.33~27.66℃,盐度的变化范围为9.16~31.5,p H的变化范围为7.45~8.51,溶解氧的变化范围为5.50~11.45 mg·L-1。通过对赤潮期间的环境因子分析,并结合2006年该海域发生的双胞旋沟藻赤潮事件和近几年周边海域发生赤潮的情况,得出以下结论：2009年珠海双胞旋沟藻赤潮规模较大,是中国沿海由双胞旋沟藻引起的最大规模赤潮。10月25日─10月27日为赤潮的起始发展阶段,10月28日─11月1日为赤潮形成维持阶段,11月2日─11月6日为赤潮消亡阶段。赤潮生消过程浮游植物群落结构发生了变化,赤潮持续期双胞旋沟藻占主要优势,赤潮消亡期间硅藻（骨条藻Skeletonema spp.和角毛藻Chaetoceros spp.）数量增加,演替双胞旋沟藻成为优势种。此次赤潮事件中有机氮浓度较高,约占总氮的60%,是赤潮藻大量繁殖代谢所致。研究海域处于严重富营养化水平,这是诱发赤潮发生的基础。同时,长时间处于高温、低盐的环境,使双胞旋沟藻急剧繁殖,诱发赤潮。在赤潮后期,恶劣的气象条件是赤潮消退的主要原因。

The bloom of Cochlodinium geminatum Sch＆#252;tt in the Pearl River Estuary was monitored for 10 days （from October 28th to November 6th） in order to explore its evolution. Accordingly, three monitoring sections which include 12 sites in total were set up. Dynamics of the algae density, chlorophyll a, nutrient, temperature, salinity, pH and dissolved oxygen were studied by field monitoring and laboratory analysis. The results showed that the algae density increased firstly and then decreased, with the highest density at 2.765＆#215;107 cells·L-1. The content of Chlorophyll a rose firstly and then decreased, with the maximum at 172.76 μ·L-1. Inorganic nitrogen and inorganic phosphorus were both at the level of eutrophication, in which inorganic nitrogen increased firstly and then decreased, and rebound at the end of the red tide;while inorganic phosphorus showed an overall downward trend. The water temperature in the red tide area ranged between 19.33 and 27.66 ℃, the salinity changed in the range of 9.16~31.5, pH changed in the range of 7.45~8.51, and dissolved oxygen changed in the range of 5.50~11.45 mg·L-1. Through the analysis of environmental factors during the red tide, in combination with the Cochlodinium geminatum bloom of the waters in 2006, and the bloom events occurred in surrounding waters in recent years, the following conclusions could be obtained：the bloom of Cochlodinium geminatum in Zhuhai waters in 2009 was in very large scale, and was the largest-scale bloom caused by C. geminatum in the Chinese coast. The initial stage of the bloom was from October 25th to October 27th, the maintenance stage was from October 28th to November 2nd, and the extinction stage was from November 2nd to November 6th. The community structure of phytoplankton had changed during the bloom evolution： in the maintenance stage, the Cochlodinium geminatum was dominant species, while the number of diatoms （Skeletonema spp. and Chaetoceros spp.） increased, and replaced the Cochlodinium geminatum as the dominant species at the extinction stage. The organic nitrogen that was in high concentration and was about 60% of the total nitrogen was caused by metabolism of C. geminatum. Serious eutrophication was a fundamental factor for inducing a bloom, and persistent high temperature and low salinity help stimulate the massive development of C. geminatum. Bad weather condition with dropping temperature and strong wind was the driving force for dispersing nutrients, and thus terminating the bloom.