火山灰與煤灰氣膠中可溶微量金屬組成對矽藻及聚球藻生長的影響

Abstract

浮游植物對於物質生物地球化學循環及全球氣候變遷均扮演關鍵角色。微量金屬元素是浮游植物生長所必需之成分，當其缺乏或不足時會限制浮游植物生長並影響其族群結構，濃度過高時亦可能造成毒性抑制浮游植物生長。由於不同浮游植物對於微量金屬需求及毒性反應差異巨大，了解表層海洋微量金屬來源、組成及其對浮游植物生長與族群結構的調控，是本研究的主要目的。氣膠為遠岸海洋表層水體中微量金屬主要來源，沉降於海水之氣膠中重金屬是否為生物可利用形態是影響浮游植物生長與其族群結構的關鍵因素，了解不同氣膠於水中微量金屬溶解量亦十分重要，本實驗室先前研究發現南海浮游生物體表吸附大量重金屬，該金屬主要來自人為活動所產生之氣膠；之後又證實人為活動所產生之氣膠，為南海表層海水微量金屬主要來源。除了人為活動產生之氣膠外，另一天然岩石性氣膠，火山灰，亦是海洋表層微量金屬重要來源。本研究分析並了解煤灰氣膠與火山灰中可溶性及總微量金屬濃度及其相對金屬組成，並以該相對組成所配製之培養液來進行藻類養殖，本研究選取原核及真核浮游植物具代表性之模式藻種Synechococcus sp.及Thalassiosira weissflogii，觀察該培養液中之金屬組成對其生長之影響及細胞金屬組成變化。參考過去實驗室培養結果，推測本研究中氣膠所溶出組成及所選定金屬濃度範圍，對於矽藻所需鐵的生物可利用濃度可能不足，銅及鎘的濃度對聚球藻而言則將產生毒性。本實驗亦發現在水中重金屬濃度相對過高時，浮游植物將吸附大量顆粒態之重金屬，顯著提高其細胞整體之重金屬濃度。

Bioactive trace metals in seawater play important roles in influencing global biogeochemical cycles and oceanic ecosystem dynamics. When the concentrations of the trace metals are depleted, the metals may become limiting and co-limiting factors for phytoplankton growth. In contrast, when the concentrations of some bioactive trace metals are elevated, the metals can become toxic to some marine phytoplankton. The concentrations and the composition of the whole suite of the trace metals in seawater are thus essential to fully understand trace metal biogeochemistry in the ocean and their limitation or toxicity to phytoplankton growth in marine environment. Aerosols are major trace metal source in the surface water of marine offshore waters. It is believed that soluble trace metals in aerosols are bioavailable to marine phytoplankton. The major objectives of this study are to determine soluble and total trace metal composition in coal burning ashes and volcanic ashes then to investigate the effects of the composition on Thalassiosira weissflogii and Synechococcus sp. growth. The results indicate that the Fe concentration level in the composition may become a limiting factor for Thalassiosira weissflogii growth and the Cu and Cd concentration levels may be toxic to Synechococcus sp. growth. When the concentrations of particle reactive trace metals are over their maximum soluble concentrations in seawater, phytoplankton serves as major agents to adsorb particulate trace metals and significantly elevate their cellular trace metal composition.