- 學位論文
水質化學及耳石微化學在淡水河流域烏魚的洄游環境史之應用研究
Migratory environmental history of grey mullet in Tanshui River System revealed by water chemistry and otolith microchemistry
摘要
摘要 耳石微量元素組成已被廣泛應用於魚類洄游環境史之研究。前人的研究指出，海水的鈣(Ca)、鍶(Sr)元素濃度平均高於河水，相反地河川的鋇(Ba)元素濃度則顯著高於一般海水。實驗也證明魚類耳石中的元素組成與水中的元素組成相關。因此耳石Sr/Ca比值及Ba/Ca比值變化成為調查兩側洄游型魚類的洄游環境史的指標性工具。河口域環境受潮汐作用及人為汙染影響，不同河段的化學組成會有所差異。利用耳石Sr/Ca比及Ba/Ca比的時序列變化除了可以重建河口域魚類洄游環境史之外也可了解河口的人為汙染。 本研究於2009年9月至2011年5月期間自淡水河流域主流及其支流基隆河、大漢溪、新店溪及景美溪五個河段的45個水樣採集點，進行5次水樣採集及水質測量。並從過去的研究團隊於2006年8月至2010年8月期間自相同採樣點所採集的烏魚樣本及其利用EPMA所測量的69個耳石Sr/Ca比值，以及利用LA-ICPMS所測量的 12個耳石樣本的Sr/Ca比值與Ba/Ca比值。與各測站所測得的水中Ba、Sr、Ca濃度對照，探討淡水河烏魚耳石微化學與水質化學之關係，藉此了解烏魚在淡水河的洄游行為與棲地利用特徵。結果總結如下： (1) 水中Sr、Ca元素的濃度與鹽度成正相關係，其R2分別為0.82 ~ 0.95及0.93 ~ 98，亦即鹽度的變化可以解釋淡水河Sr濃度82 ~ 95%以及Ca濃度93 ~ 98%的變化。換言之，淡水河Sr及Ca的主要來源是由海水所貢獻，人為汙染的影響較輕微。 (2) 水中Ba元素的濃度與鹽度成反比關係，其R2 = 0.01 ~ 0.07，亦即鹽度僅能解釋1 ~ 7%的Ba濃度變化。Ba濃度普遍在河流中段河海水混和區較高，但在支流的幾個特定採集點有異常升高情形，顯示Ba是淡水起源，並可能受人為汙染影響。 (3) 在淡水河主流部分的水中Sr濃度變化極大，並與上游的三個支流之間有顯著差異。水中Ba濃度在淡水河主流與大漢溪感潮帶之間無顯著差異，但主流與新店溪及基隆河之間卻有顯著差異。 (4) 耳石Sr/Ca比值與Ba/Ca比值基本上呈現反比關係，但有時不一定反映此一關係，其原因可能是河川中的Ba濃度，除了淡水起源的影響之外，也受河川水與海水混合時的化學變化所影響。 (5) 烏魚仔稚魚時期偏好生活於餌料豐富的淡水河主流中上游一帶，隨年紀漸長，有上溯至上游各支流的傾向。接近性成熟年齡時會再次回到淡水河主流中上游補充能量為出海產卵做準備。大部分烏魚集中在潮汐交會區，此現象與耳石微化學信號一致。 根據上述結果歸納得知，利用耳石Sr/Ca比值回推烏魚在淡水河的洄游環境史是可行的。加上耳石Ba/Ca比值的輔助，可以進一步看出烏魚在淡水河匯流區及上游的棲地利用的移動行為。
並列摘要
Abstract Otolith microchemistry has been validated to be a powerful tool in studying the migratory environmental history of fish. The chemical composition in otolith of fish is affected by the ambient water the fish inhabited. The migratory environmental history of the grey mullet, Mugil Cephalus in the Tanshui River was studied by the water chemistry particularly Ba, Sr and Ca, and the elements in the fish otolith. The water samples were collected from 45 sampling stations in the Tanshui River Basin over 5 times from September, 2009 to May, 2011. The data of otolith Sr/Ca ratios of 69 grey mullets and Ba/Ca ratio of 12 grey mullets were obtained from the other studied which was measured by EPMA and LA-ICPMS based on the specimens collected in the same river system from August 2006 to August 2010. The results are summarized as follows: (1) The contents of Sr and Ca in water were positively correlated to salinity (R2=0.82~0.95 for Sr and R2=0.93 ~ 98 for Ca. It indicates that Ca and Sr are mainly contributed by sea water and scarcely influenced by artificial contaminant. (2) The content of Ba in water was negatively correlated to salinity but the correlation is very weak (R2=0.01 ~ 0.07). The Ba content was higher in the middle reaches, the upper limit of the seawater intrusion, and showed unusual high contents in some sampling sites in upper reaches. It reveals that Ba originates from freshwater and might be influenced by artificial contaminant. (3) The content of Sr in the water significantly increased with increasing salinity, but Ba content decreased with increasing salinity and appeared a peak at tidal mixing areas of the river where turbidity was maximum. (4) The temporal changes of Sr/Ca ratios and Ba/Ca ratios in otolith provided the opportunity to study migratory environmental history of the mullet in the river. (5) The grey mullet in larva stage preferred staying in the main river of Tanshui River for the rich foods, than migrated to the three upstream in growth-phase young stage. During maturation, they migrated back to the sea for spawning. The mullet seems to concentrate in the tidal mixing area. This tendency is consistent with the signal of otolith microchemistry of the fish. In conclusion, Sr/Ca ratios and Ba/Ca ratios in otolith of the mullet in river can reflect complicated dynamics of the water. It is reliable to use the elemental composition in the otolith to reconstruct the migratory environmental history of grey mullet in Tanshui River.
參考文獻
延伸閱讀
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