以耳石微細結構及穩定性同位素組成分析核電廠溫排水對於河鱸生活史的影響

Abstract

立陶宛境內的Ignalina核能發電廠利用Lake Drūkšiai作為冷卻水來源，此湖泊長期(1984-2009)受到核電廠溫排水注入，使湖泊水溫上升，並造成湖泊中魚類群聚的改變。為檢視溫排水對河鱸(Perca fluviatilis)所造成的影響，本研究以魚類耳石為研究材料，透過耳石碳氧同位素組成分析及耳石輪紋回推體長，檢視Lake Drūkšiai中河鱸的生活史，並與不受溫排水影響湖泊(Lake Plateliai及Lake Sventes)中的河鱸生活史進行比較。耳石穩定性氧同位素結果顯示，河鱸幼魚時期主要棲息於高溫水域，至成魚階段則傾向停留在低溫水域，而溫排水注入所造成的水溫分布不均，則使在Lake Drūkšiai中的河鱸於成體之後，發展出不同的棲地使用策略；部分個體的活動範圍遠離受溫排水影響區域，僅經歷季節性的水溫變化，其餘個體則廣泛使用湖泊水域，並可能跨越受溫排水影響的加溫水域，因此在季節性水溫變化外，同時遭遇異常的水溫起伏。另一方面，穩定性碳同位素結果顯示，Lake Drūkšiai中河鱸的生理代謝亦出現異於其他湖泊中河鱸的變化趨勢。而由耳石輪紋進行河鱸體長回推的結果發現，Lake Drūkšiai與其他湖泊相比有較大體長，表示受溫排水影響的Lake Drūkšiai其棲地環境促進河鱸成長。綜合本研究結果，發現溫排水的注入造成Lake Drūkšiai中河鱸的棲地利用改變，不僅對魚體生理代謝造成影響，並且加速魚體成長。

Lake Drūkšiai had been used as the cooling system of Ignalina Nuclear Power Plant (INPP) in Lithuania since 1984 to 2009, and the thermal discharge had altered the aquatic environment, where fish species diversity and community structure were also changed. In order to evaluate possible effects of thermal discharge on aquatic organisms, the life history of perch (Perca fluviatilis) in Lake Drūkšiai is examined by fish otolith microstructure and microchemistry. For comparison, perch from other nature lakes (Lake Plateliai and Lake Sventes) were also analyzed. Stable oxygen isotopic composition shows that perch larva and juvenile had spent a specific period of time staying in warm habitat, and went into cooler zone afterward. Furthermore, different strategy of habitat use is evaluated for perch adults; some individuals had stayed away from the main thermally affected area, and experienced seasonally water temperature changes only, though others had widely used the whole lake, including the main affected area, and went through obvious water temperature fluctuation. From stable carbon isotopic composition results, metabolic rates of perch were also changed by the thermal shift in Lake Drūkšiai. Moreover, back-calculated fish length shows that perch had better growth in Lake Drūkšiai than in natural lakes, which suggests the thermally changed lake had provided favorable conditions for perch growth. In this study, the effect of thermal discharge on perch is evaluated, and the results indicate that thermal discharge had indeed altered the life history of perch.