桃園台地老街溪河床沉積物與孔隙水中之砷分布特性與時空變異;Distribution characteristics and spatiotemporal variability of arsenic in riverbed sediment and pore water along the Laojie River on the Taoyuan Tableland

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Title:	桃園台地老街溪河床沉積物與孔隙水中之砷分布特性與時空變異;Distribution characteristics and spatiotemporal variability of arsenic in riverbed sediment and pore water along the Laojie River on the Taoyuan Tableland
Authors:	劉子榕;Liu, Tzu-Jung
Contributors:	應用地質研究所
Keywords:	碳酸鹽;鐵錳氧化物;砷;物種砷;孔隙水;時空變異;連續萃取;carbonate;iron manganese oxide;arsenic;arsenic speciation;temporal variability;pore water;sequential extraction
Date:	2020-08-19
Issue Date:	2020-09-02 19:18:12 (UTC+8)
Publisher:	國立中央大學
Abstract:	砷污染屬世界性的環境污染問題，由其在亞洲也有多起汙染，但前人研究多半是以地下含水層為研究區域，較少有針對地表開放水體之砷污染作探討，台灣也是砷污染非常嚴重之區域，雖然近年來污染防治逐漸有成但多半是以沖積扇區域研究為主，故本研究已台灣西北部桃園市境內之老街溪作為研究區，逐季採集並分析不同距離之河川水(n=11)、孔隙水(n=8)、淺層河床沉積物(n=8)。本研究旨在了解總砷濃度在河川水、孔隙水、及河床沉積物中的砷濃度之時空變異以及砷物種變化，同時使用基礎水化學成份計算相關分析與因子分析得到影響參數以及使用X射線繞射儀(XRD)鑑定河床沉積物之主要礦物，並用連續萃取試驗了解砷之固體吸附相。研究顯示老街溪河床沉積物之連續萃取試驗中的沉積物內砷主要的固體吸附相為碳酸鹽類、錳氧化物、鐵氧化物等，其中鐵、錳礦物對砷具有氧化及催化能力且鐵在孔隙水(相關係數=0.547~0.934)與沉積物(相關係數=0.916~0.965)中具高度顯著相關性。因子分析的結果指出河川水與孔隙水之水質主要受離子交換效應與農業汙染效應以及水岩效應影響。在砷的時空變化上，總砷濃度在河川水、孔隙水及河床沉積物上面皆沒有顯著的時間變化，砷每季之濃度於孔隙水與沉積物在空間上具規則性的反比趨勢，兩者之砷濃度會互相影響及有釋放之關係，呈現結果為在秋季(2019年九月)的平均砷濃度最高但在冬季(2019年十二月)最低(秋季與冬季之孔隙水砷濃度:3.38μg/L、1.625μg/L;沉積物:4.357 mg/kg、2.602 mg/kg)，物種砷在冬季(As(III)> As(V))比夏季更有區分性，孔隙水內含氧量較夏天高且水溫低，故沉積物上As(V)為主要吸附價態，孔隙水則以As(III)為主。在單因子變異性分析上沉積物與孔隙水無論在時空變異上皆有相似之高度變異性，在空間上，上游與下游還有夏、冬季與夏、秋季兩組皆為高度顯著變異，此結果與一般沖積含水層的砷分布特性有所不同,有待後續研究確認。;Arsenic pollution was recognized to be an important environmental problem. Most relevant studies have focused on the groundwater systems in alluvial fans. This study aims to assess the spatial and temporal distributions of arsenic concentration and the variations of arsenic species along the Lao-jie River in Taoyuan City, Taiwan. The river sediment, pore water, and surface water (river) samples were taken at selected locations along the Lao-jie River. Twenty-six samples were collected for chemical anayses, in which 10 for surface water, 8 for pore water, and 8 for shallow river sediment. At the same time, the correlation analysis and factor analysis on the basis of chemical composition of water are used to obtain the influencing parameters, and the X-ray Diffractometer (XRD)was used to identify the major minerals in riverbed sediments. The results of sequential extraction experiments on the riverbed sediments of the Laojie River have shown that the main adsorbed phases of arsenic in the sediments are carbonates, manganese oxides, iron oxides and other environmental substrates. Iron-manganese minerals have the ability to oxidize and catalyze arsenic, which are highly correlatedin pore water (correlation coefficient= 0.547~0.934) and sediment(correlation coefficient= 0.916~0.965). The results of factor analysis suggest that the water quality of river water and pore water can be affected by the effects of ion exchange, agricultural pollution, and water-sediment interaction. In terms of the spatial and temporal variations of arsenic, there was no significant temporal variations in the total arsenic concentration both in pore water and sediments. The concentrations of arsenic in pore water and sediments for each season show regularly and inversely proportional. The arsenic concentration can be mutualy affected between pore water and sediments probably due to water-sediment interacion. This gave rise to the highest As mean concentration in autumn (September 2019 ) and the lowest in winter (December 2019) (the concentrations of As in pore water and sediments in autumn and winter: 3.38μg/L and 1.625μg/L for pore water; 4.357 mg/kg and 2.602mg/kg for sediment, respectively), in which the arsenic speciation (As(III)> As(V)) in winter is more distinct than in summer. Therefore, more pentavalent arsenic was adsorbed on the sediment, whereas more As(III)was present in pore water. The results of univariate analysis (ANOVA) show highly significant spatio-temporal variations in arsenic concentrations both in sediments and pore water in which both spatially in the upstream and downstream areas and temporally for summer vs. winter and summer vs. autumn. This result is obviously different from the distribution characteristic of arsenic in an alluvial aquifer, which warrants a future research .
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