2:30 PM - 2:45 PM
[AHW27-16] Seasonal change of the major and trace elements of Red river water, northern Vietnam.
Keywords:Vietnam, Red River, Arsenic, Seasonal Change
Range of total arsenic concentration of riverwaters from the main channel are 1.4-9.1μg/L in the rainy season and 2.2-92.9 μg/L in the dry season. Total arsenic concentrations were 9.2 μg/L in the rainy season and 33.9 μg/L in the dry season near Lao Cai. Although arsenic concentration is less than the WHO standard (10 μg/L) in the rainy season, the concentration in the dry season was much higher than the standard. Arsenic concentration decrease toward downstream from Lao Cai. Around Ha Noi, located in about 300km downstream, total arsenic concentration was 1.4 μg/L in the rainy season and 3.8 μg/L in the dry season. In both seasons, range of total arsenic concentrations of branches are lower than those of the main channel. 40% of arsenic was dissolved near Lao Cai, and the ratio of dissolved arsenic increase toward downstream. Finally, most of arsenic was dissolved near Ha Noi.
The oxygen and hydrogen isotope ratios of riverwaters were plotted on the GMWL (δ2H=8*δ18O+10). Most of the δ18O of branch waters were lower than those of main channel in the rainy season, while higher in the dry season. Inflow from the branches influenced the isotope compositions of main channel waters through the year, especially in the rainy season when precipitation was abundant.
Total arsenic concentration of main channel water decreased due to the inflow of diluted branch waters. Also, the arsenic would be removed from the riverwater in association with sedimented particles on the riverbed.