长江口甲藻孢囊与水体富营养化和厄尔尼诺指数关系研究

Relationship between dinoflagellate cysts and water eutrophication and ENSO index in the Changjiang River Estuary

甲藻孢囊是一种可用于追溯环境变化历史的生物微化石,如指示水体富营养化和气候变化,但是如何指示水体富营养化存在争议,并且如何区分甲藻孢囊中的水体富营养化信号和气候变化信号也是一个科学难题。为了研究这两个科学问题,我们利用长江口海域受到水体富营养化和厄尔尼诺事件双重影响的特点,在该海域不同位置采集了4根沉积柱,分析了其中的甲藻孢囊。结果显示,长江口海域水体富营养化会引起总甲藻孢囊以及产麻痹性贝毒甲藻孢囊丰度上升,并且导致异养型和自养型甲藻孢囊的比率下降,这说明引起长江口海域富营养化主要原因还是以氮、磷、钾为主导的农业和生活污水。受长江冲淡水流影响,这种富营养化信号在近处相对较弱;中间处信号明显;远处信号几乎未见。同时入海口近处高沉积速率沉积柱样的分析结果显示,甲藻孢囊丰度存在季节性的变化规律,其中以冬季甲藻孢囊丰度最低,推测低温起了主导作用。而厄尔尼诺气候事件可以通过影响陆地径流从而改变陆源营养盐的输入来改变甲藻孢囊丰度,反映在沉积柱中的信息即为甲藻孢囊丰度峰谷值的出现。该信号也随距离入海口的远近不同而不同:近处受水流突然增大或减弱导致甲藻孢囊丰度谷值和峰值出现;中间处水流与甲藻孢囊丰度峰谷值重叠且信号较强;远处丰度峰值信号明显但主导因素多样化。这些结果对该海域环境演变历史重建,赤潮发生历史和厄尔尼诺现象研究都具有十分重要的科学意义。

Dinoflagellate cysts,as micro-fossil,could be used to trace environmental change history,such as water eutrophication and climate change.But there is controversy on how to indicate water eutrophication,and also it is a problem how to differ the signals between water eutrophication and climate change in dinoflagellate cysts.In order to address these problems,we collected four sediment cores in the Changjiang River Estuary and analyzed their dinoflagellate cysts.Results showed that eutrophication could lead to the increase of total dinoflagellate cysts and Paralytic Shellfish Poisoning(PSP)productive dinoflagellate cysts abundance.And the ratio of hetero/autotrophic dinoflagellate cysts decreased,which implied that the eutrophication mainly resulted from agriculture and domestic sewage in the Changjiang River Estuary.Because of water plume,the eutrophication signal was relatively weak near estuary, strong in middle distance and almost none in far distance. Seasonal change of dinoflagellate cysts wasobserved in the high sediment sinking area in the estuary, with the lowest production in winter as a result of lowtemperature. ENSO events will lead to the peak and valley value of dinoflagellate cysts abundance by affecting nutrientinput which is transferred by river downloading. Moreover, the signal also varied with the distance: valleyand peak value of dinoflagellate cysts present because of strong and weak river runoff pulse near estuary, peak andvalley value of dinoflagellate cysts and runoff overlapped and were clear in middle distance, and peak value of dinoflagellatecysts was obvious in far distance but the domain reason was complex. These findings are of great significanceto environment history reconstruction, study of red tide history and ENSO events.