Abstract: Characteristics of concentration distribution of total dissolved iron and its correlation with organic matter and pH value in Songhua River and Heilongjiang River were studied.Results show that the concentrations of total dissolved iron ranged in 0.10-0.62 mg·L^-1 in Heilongjiang River,and in 0.11-0.73 mg·L^-1 in Songhua River.The mean concentrations of both total dissolved iron and ferrous iron in Songhua River were slightly higher than that in Heilongjiang River.Within a year,the peak concentrations of dissolved iron appeared mostly in the moderate flow period.A significant negative linear relationship was observed between COD_Cr and ferrous iron in Heilongjiang River,but a significant positive linear relationship between COD_Cr and total dissolved iron and significant negative linear relationships of ferrous iron with BOD₅ and pH were observed in Songhua River.Input of hard-to-biodegrade organic substances from anthropogenic sources increases the concentrations of both total dissolved iron and organic-chelated iron.

Key words: organic matter, total dissolved iron, COD_Cr, BOD₅, pH value, Songhua River, Heilongjiang River