Stable Isotopic Study of Macrophytes of Taiwan Estuary

穩定同位素在地球化學上的應用十分廣泛，尤其在作為污染的追蹤劑、食物鏈研 究、環境變遷的因子等（Macko & Ostrom, 1994 ；Michener & Schell, 1994 ；Cabana & Rasmussen, 1996 ；Meyer,1997 ；Holloway & Dahlgren, 1999 ；Peterson, 1999 ）。在之前的 研究計畫中，我們發現沉積物的氮同位素在這些環境中，除了用來作為生產力以及營養 鹽變化的指標之外，亦受到水體中大型浮游植物的生長所影響，對於鹽度的變化似乎也 有一定程度的相關性。本計畫預定以淡水河口、西南地區潟湖環境的沈積物以及現生大 型浮游植物為研究對象，分析其中所含有機物質的氮同位素，佐以碳、硫同位素和碳氮 比，希望能釐清生長在潟湖環境的大型浮游植物的生長與沉積物氮同位素值之間的關 係，並將其穩定同位素的值建立資料庫，使得應用穩定同位素於作為指示環境變遷的因 子提供更多資訊，在古環境的解釋上得以更加可靠：並期能對之前在西南地區以及臺北 盆地氣候變遷研究的結果有一更詳盡的解釋。Stable isotope analysis is of importance and can be widely applied in geochemical study, especially in studying pollutions, food webs, and environmental changes (Macko & Ostrom, 1994 ；Michener & Schell, 1994 ；Meyer,1997). However, the information that derived from sediments could not perfectly discribe the paleo-productivity and nutrient situation of water body. The nutrient situation will be changed because of catchment vegetation, erosion of riverine rock, dry deposition, human activities, and aquatic productivity. Once the nutrient situation is changed, the population of primary production would be influenced. For example, eutrophication happens when the supplement of nutrient is too high (Voss & Struck, 1997). Based on our previous study of the southwestern coastal plain and Taipei Basin, we found that there is some sections that the nitrogen isotopic values became heavy. Based on our analysis the surface sediments of Chiku lagoon, we found different δ 15 N from 4 to 12‰ according to different position and salinity .The probable reason may be the influence of growth of high δ 15 N macrophyte in the semi-salty water of estuarine environment. In order to understand how the macrophyte affect the δ 15 N of sediments, in this study, we will analyze the nitrogen isotope of sediments and macrophyte sampled from the estuary of Tanshui River and southwestern coastal lagoons, accompanied with carbon and sulfur isotope and C/N ratio, to understand the relationship between the growth of macrophyte and the isotope values of sediments. Furthermore, we will try to establish the database of lagoonal macrophyte in order to efficiently use stable isotopes as proxies to understand the environmental change and reconstruct the paleo-environment