Spatial and temporal variations of water quality in the Han River and its tributaries, Seoul, Korea, 1993-2002

Spatial and temporal variations of eight selected water quality measurements were examined for the 26 stations located in the Han River and its tributaries within the city of Seoul from 1993 to 2002. The eight measurements are water temperature, pH, dissolved oxygen, biochemical oxygen demand, chemical oxygen demand, suspended solid, total nitrogen and total phosphorus. There is no discernable increase or decrease in water quality measurements in four representative stations. A striking longitudinal variation of all water quality measurements is detected for eight stations along the Han River. Water quality dramatically decline in the middle section of the Han River where the river receives inputs from polluted tributaries. All water quality measurements, except pH, exhibit better conditions in the main river group than its counterpart tributary group. The 26 stations can be grouped into three main clusters; (1) the main river and its tributaries that have relatively good water quality, (2) the tributaries that have medium water quality, and (3) the tributaries nearby industrial sites that are heavily polluted.