北投地熱谷溫泉之砷含量高達4.6 mg/L，含砷之溫泉水可能沿著地表溪流與地下水補注之傳輸過程進入下游之關渡平原、關渡濕地及淡水河口生態系統，然而目前研究鮮少探討濕地系統中砷之循環與分佈。本研究針對關渡濕地之沉積物與孔隙水進行化學定量分析，探討砷與其他相關化學物質在濕地之空間分佈，再根據前述分析結果挑選適當沉積物樣本進行多段式連續萃取，判別與砷富集有關之礦物相別，並初步推論砷可能之地化反應與循環，此外藉由高解析電子能譜儀(HR-XPS)及掃描式電子顯微鏡暨能量分散光譜儀(SEM-EDS)進行表面化學分析，以確認與砷相關之礦物成分。由研究結果顯示表層沉積物，砷與鐵之釋出受氧化條件之影響，因此其孔隙水中砷與鐵含量較低，而底部沉積物屬還原環境，沉積物含量隨深度逐漸升高，有利於含砷之鐵(錳)氧化物之還原反應，造成砷與鐵(錳)之溶解釋出，然而於更深之地層環境，大量硫酸鹽於此環境亦發生還原作用而產生硫化物，此過程可能吸附由鐵(錳)氧化物還原釋出於孔隙水之砷，造成底部孔隙水中砷含量降低且鐵(錳)離子增加之現象，連續萃取之分析結果指出濕地沉積物中砷主要以吸附或沉澱作用，累積於無晶形與結晶型之金屬氧化物。最後根據HR-XPS與SEM-EDS結果，砷於關渡濕地沉積物主要吸附於鐵(錳)氧化物與黃鐵礦，其分布與移動受氧化還原狀態改變之影響。As concentration of Beitou geothermal spring water was up to 4.32 mg/L . High As contents may be mobilized to downstream of coastal plain, wetland, and estuary ecosystem. However, both the cycling and distribution and of As in the wetland ecosystem are still poorly defined at present. The purpose of this study is to analyse with chemical and mineralogical characterization(HR-XPS and SEM-EDS) methods to determine the spatial distribution of arsenic between aqueous and solid phase and mineral assemblages.In addition, the sequential extraction procedures is applied to estimate the As form in mineral phase.In upper sediment , free As and Fe species in aqueous phase was restrained by oxidation condition, causing a low concentration of arsenite and ferrous iron. Highest As and Fe concentrations in pore water were found at Fe-reducing depth and suggesting from reductive dissolution of As-contained Fe oxides. A decrease of solid phase Fe/Mn contents with depth in both cores suggested that reductive dissolution of Fe/Mn oxides in the lower layer was likely to occur with increasing organic matter. In the lower layer, aqueous As concentrations were constrained by reducing condition causing precipitated sulfide minerals and retained on particles of lower layer sediment. Most of extracted As concentrations were incorporated in amorphous and crystalline metal oxides. Based HR-XPS and SEM-EDS, distribution and mobilization of As in this wetland systems is primarily associated with Fe/Mn oxides and pyrite, which governed by the ambient redox condition.
