Chromatographic Determination of the Seasonal Variation and Rainfall-Induced Fluctuation in the Concentration and Composition of Dissolved Humic Substances in River Water

Abstract

The relative concentration and composition of dissolved humic substances in the Oita River, Oita, were measured over a two-year period from 1988 to 1989 by chromatography with pH-gradient elution. The concentration during ordinary water runoff remained at a constant level during the winter months, but increased through April into the beginning of July to reach a value about 2.5-times higher than that in the winter. A sudden lowering was observed through the middle of July into August. The concentration during high flow above 80m3 s-1 induced by rainfall increased with an increase in the flow rate; the maximal observed value was about 5-times as high as that during ordinary water runoff. The extent of the increase was greater for components eluting in a higher pH region than in a lower pH region. An imitative test suggested that scouring of autochthonous humic substances in bottom sediments of the river was one contribution to the concentration increase and the composition change. Thus, the chromatographic method employed permitted us to obtain detailed information concerning seasonal variations and violent rainfall-induced fluctuation.