Long-Term Variations of Water Quality in the Sagami River and its Tributaries. III. Down Stream Trend.:—Down Stream Trend—
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概要
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We investigated long-term time variation of dissolved species in the water sampled from the down stream of Sagami River and its tributaries. The sampling had been done monthly from May 1993 to April 2000 at 11 sampling sites of down stream of Sagami River water system. Twenty-four major to trace elements (Li, Mg, Al, Ca, V Mn, Fe, Co, Ni, Cu, Zn, As, Rb, Sr, Mo, Ag, Cd, Sb, Cs, Ba, W, TI, Pb, U) were determined using conventional Q-pole ICP-MS with direct nebulization. Electric Conductivity, pH, water flux (from April 1995), major anion (from September 1996 by ion chromatography), Na, K (from December 1996 by AAS) were also determined. Long-term interannual trends of dissolved species were examined for the data accumulated for 7 years by 12 months moving average.<BR>Some small tributaries seemed to be polluted by either industrial or domestic wastewaters especially for Mn, Ni, Mo and Tl. The concentrations of these elements in the tributaries were 30 to 100 times higher in average than those in main stream. Consequently the concentrations of the elements in main stream were significantly affected by the tributaries though their water flux were less than 1/20 of main stream. Rather sharp decreasing trends during the monitoring period, however, were observed for these contaminant elements. This may be because (1) the regulation standard for wastewater discharge was revised in 1994, (2) availability of municipal sewage increased, (3) industrial activity decreased with economical recession.<BR>In mainstream, 12 months moving averages of Li, Al, V As were generally constant with irregular or seasonal variations, while Mn, Ni, Mo, W, which are affected by small tributaries, had decreasing trend. Mg, Cu, Rb, Sr, Sb, Cs, Ba, U showed broad hump during 1995 to 1997 with small monthly variation. Though precipitation of this period was rather small, the correlation between the concentrations of these elements and the precipitation were not clear.
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