流經都市之河川於感潮帶河海水混合時溶解鐵的氧化還原狀態

本研究藉由物理分離與化學分析方法-菲洛琳(ferrozine)分光偵測法，探討淡水河流域自關渡碼頭至出海口間，在潮汐混合作用下，水中溶解態鐵含量比例以及鐵物種的分布情形。先以正壓過濾法將水樣通過0.45 μm的濾球與0.025 μm濾膜(nanofiltration)，將淡水河中鐵區分為總溶解態(total dissolved type, <0.45 μm)、膠體態(colloidal type, 0.025 μm-0.45 μm)與分子態(<0.025 μm)，之後加硝酸、照UV進行消化處理，所得的水樣以菲洛琳呈色後再以分光光度法進行分析，最後得到不同分子量 (<0.45 μm，0.025 -0.45 μm，<0.025 μm)的鐵。本次研究結果顯示，在淡水河河口所測得的溶解態鐵(Fe<0.45 μm)濃度約0.1- 4.0 μΜ，依分子量大小的分離結果得知淡水河中下游處主要相態為膠體態鐵，分子態則佔少數，水體中鐵分子或化合物主要是以0.025 μm-0.45 μm的膠體態鐵形式存在，其中有部分是0.025 μm-0.45 μm的高分子量化合物或次微顆粒態，而所測到的高分子量的鐵除了主要有Fe(Ⅲ)外也含有Fe(Ⅱ)，同時，所測量的低分子量鐵除了為Fe(Ⅱ)外也含有Fe(Ⅲ)，推測原因Fe(Ⅲ)的來源可能是有機錯合水解或由沉積物釋出Fe(II)後再度氧化或由土壤釋出造成。另一方面，由於在海水與淡水匯流之處因鹽度梯度變化，造成水體氧化還原變化劇烈，因Fe(Ⅱ)與Fe(Ⅲ)互變頻繁。而在河口處也觀察到非守恆型的清除作用發生，造成淡海水交會之處鐵物種的大量流失現象。

關鍵字

鐵；膠體鐵；物種變化；淡水河河口

並列摘要

Physical separation (in-line filtration, stirred cell nano-filtration) and colorimetric methods were used in this study to determine the redox couple Fe(II)/Fe(Ⅲ) in truly dissolved (<0.025 μm) and colloidal (0.025~0.45 μm) phases from waters of a tidal estuary, Danshui River estuary. This study shows that concentration of dissolved iron(Fe<0.45 μm ) in Danshui River estuary ranges from 0.1 to 4.0 μM . In terms of the results based on molecules weight separation，iron of colloidal phase accounts for the majority in the middle and lower reaches of Danshui River, only a few iron remain in molecule phase. Most of iron and compounds that chelate iron existed in colloidal form which size ranged from 0.025-0.45 μm. Soluble iron(<0.025 μm) nearly at constant fraction, and most of them are Fe (II).Some iron species are compounds of high molecule weight or sub-particles phase, and these ferruginous compounds of high molecule weight contains not only Fe(III) but also Fe(II). Similarly, iron of low molecule weight is mainly composed of Fe(II), and also there are a few Fe(III) existed, which is caused by oxidation of Fe(II) in release of the benthic sediments and hydrolysis of iron-chelated organic compounds. In addition, with salinity gradient variation in the transition between river and ocean, intense re-oxidation reactions occurred there caused interconversion Fe(II) and Fe(III), meanwhile , non-conservative scavenge also led to great loss of iron species.