河口付近の水質遷移を中心とするバンコク，ダッカ周辺河川・運河の感潮域の水質分布

Abstract

Field surveys were conducted in rivers/canals in peri-urban areas of Dhaka and Bangkok in October and December, 2006. The distributions of turbidity and chlorophyll-a (Chl-a) concentrations on a graph could distinguish the measurement results of four water bodies, the Shitalakhya River, Bangladesh, and the Chao Phraya River, Tha Chin River and Tamru Canal, Thailand. Chl-a concentrations were 2∼4 μg l-1 in the Shitalakhya River, 4∼6 μg l-1 in the Chao Phraya River, 5∼13 μg l-1 in the Tha Chin River, and 12∼35 μg l-1 in the Tamru Canal. Moderate mixing was observed near the river mouth, and the turbidity maximum and Chl-a maximum were observed in the Tha Chin River estuary. Salt water intrusion was not observed in the Tamru Canal, the reason for which should be the water depth being smaller than the critical minimum water depth of salt water intrusion. In the Tamru Canal, the turbidity maximum and Chl-a maximum were observed both in the upper canal and at the canal mouth, which should be typical of eutrophicated and shallow coastal rivers/canals. Vertical water quality profile monitoring including nutrients and Chl-a concentrations is necessary to quantify land-based pollutant contributions to pollutant loads in the estuarine zone.