The spatial and temporal distribution of Arsenic speciation along Lao-Jie stream on Taoyuan tableland, Taiwan

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 Lao-jie Stream in Taoyuan City, Taiwan. The river sediment, pore water, and surface water (river) samples were taken at fixed locations along Lao-jie stream. There were 10 surface water, 8 pore water, and 8 shallow river sediment samples included in the analysis. s (n = 8). Results show that the arsenic concentration changes significantly in summer (June) and autumn (September). The phase characteristic is also different in different seasons. There is no obvious concentration change in rivers. The averaged concentration in June and September were 1.609μg / L and 1.067μg / L. However, the averaged pore water concentration was 4.089μg / L in June and was 4.829μg / L in September. The averaged concentration in shallow riverbed sediment samples were 4.435 mg / Kg in June and 6.223 mg / Kg in September. Because of stream discharge rates at different sampling times, the total arsenic concentration in autumn was generally higher than that in summer. Additionally, and the arsenic concentration for surface water and pore water showed significantly different pattern along the stream. The correlation of arsenic concentration was obtained based on samples taken from surface water and pore water in summer time. However, in the summer time the inverse proportional relation was obtained as compared with the arsenic concentration obtained from the shallow sediments. In autumn, the arsenic concentration in the pore water samples is proportional to the arsenic concentration in the sediment samples. The spatial distributions of pore water and sediment samples along the stream are similar. The results also showed that the arsenic concentration of sediments in the autumn was higher than that in the summer, which might be influenced by the content of iron oxide. The concentration ratios of As (III) with As (V) for pore water is 23.8: 76.2 and for sediments is 15:85 in summer. However, the ratios for pore water is 51.4: 48.6 and for sediment is 11.4: 88.6 in autumn. The As (III) in pore water increased 27.6% in autumn and As (V) in sediments increased 3.6% in winter.