| dc.description.abstract | 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 . | en_US |