颱風及極端降雨在翡翠水庫中經由上行效應對浮游生物的影響

Influences of typhoons and extreme rains on plankton through bottom-up effects in Feitsui Reservoir

黃煒忠(Wei-Chung Huang)

指導教授 ： 謝志豪

國立臺灣大學/理學院/海洋研究所/碩士(2015年)

https://doi.org/10.6342/NTU.2015.02678

摘要

由於氣候變遷，極端氣候出現的頻率也隨之增加，這些極端氣候對生態系會造成強烈的擾動。例如在湖泊生態系中，由颱風(typhoon)以及大雨(extreme rain, ER)事件所造成的強降雨(extreme precipitation, EP)，其所造成的影響儼然已成為重要議題。之前的研究指出，強降雨可以經由讓濁度上升以及由上游帶來營養鹽來對浮游植物群集造成擾動(disturbance)。然而，關於這種上行效應(bottom-up effect)是否傳遞到浮游動物以及如何傳遞的機制仍然不清楚。為了解決這個議題，我們利用在2008到2012年間在翡翠水庫發生的強降雨事件，調查了在這些事件中的強降雨前期和強降雨後期裡浮游動物群集、浮游植物生物量以及環境因子變化間的相關性。我們發現，通常濁度(turbidity)跟磷營養鹽(phosphate)會在強降雨之後上升，同時葉綠素a的濃度在強降雨過後由於光遮蔽效應而迅速下降，然後再漸漸回復至強降雨事件前原本的濃度水平。另外葉綠素a的最大值深度(the depth of the chlorophyll a maximum)也在颱風後顯著變淺。葉綠素a濃度跟最大值深度的變化說明了浮游植物主要是受到強降雨帶來的濁度上升所影響。更重要的是，浮游動物會根據其體型大小跟食性對強降雨產生不同的反應。強降雨後浮游動物的總密度上升但總生物量下降，說明了其物種組成會在強降雨後偏向較小尺寸的物種如輪蟲或小型枝腳類。我們也利用判別分析發現浮游動物的物種組成在強降雨事件後跟平日間有顯著的差異(正確率超過80%)，將強降雨事件後再細分為四個時期(以週為單位)後，每個時期彼此間的重分類正確率也接近70%。這些發現提供了強降雨會在湖泊中造成擾動且這些擾動會經由上行效應影響浮游動物的量及組成的證據。

關鍵字

強降雨 ； 颱風 ； 上行效應 ； 浮游動物 ； 浮游植物 ； 深水湖泊 ； 翡翠水庫 ； 物種組成

並列摘要

Abstract
The frequency of extreme weather events has increased due to climate change, resulting in strong disturbances in ecosystems. Extreme precipitations (EP) in lake systems caused by typhoons and extreme rains (ER) represent a pressing concern. Previous studies indicate that EP can cause disturbances to phytoplankton communities owing to increased turbidity (OBS) and nutrients (PO43-) coming from upper streams. However, whether and how these bottom-up effects can be transferred to zooplankton remains elusive. To tackle this issue, we investigated the zooplankton communities, phytoplankton biomasses, and environmental factors in both the pre-EP and post-EP periods of multiple EP events from 2008 to 2012 in Feitsui Reservoir. We found that, in general, turbidity and PO43- increased after EPs. Meanwhile, chlorophyll a decreased immediately after EPs due to light blocking effects and then gradually recovered to its original level in two weeks. In addition, the depth of chlorophyll a maximum decreased about 6 meter after typhoons. These two responses of chlorophyll a indicated that phytoplankton were mainly affected by turbidity immediately after EPs. More importantly, we found that zooplankton showed differential responses to EP events depending on their body size and feeding habit. More specifically, the species composition of zooplankton shifted to being dominated by smaller species after typhoons and extreme rains. This compositional shift resulted in a decrease in the total biomass, although the total abundance was increased. In addition, species composition of zooplankton changes significantly between the pre-EP, post-EP, and normal periods, as shown by the discriminant analysis. These findings indicated that EP events altered the physical and chemical conditions of lake environment and the disturbance can be transferred to phytoplankton and zooplankton. Both phytoplankton and zooplankton decreased in abundance, and in addition, zooplankton changed their size and species composition.

並列關鍵字

typhoon ； extreme precipitation ； bottom-up effect ； phytoplankton ； zooplankton ； deep lake ； Feitsui reservoir ； species composition

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