The Spatial Variation and Factors Controlling the Concentration of Total Dissolved Iron in Rivers, Sanjiang Plain

Abstract

AbstractThe rivers across Sanjiang Plain are an important path in transferring total dissolved iron (TDFe) into Okhotsk Sea. Distribution of TDFe in main rivers (Amur River, Ussuri River, and Songhua River) and marshy rivers (Yalv River, Bielahong River, and Naoli River) of Sanjiang Plain from 2005 to 2008 was investigated. TDFe concentrations ranged from 0.05 to 6.40 mg L−1 (mean 0.76 mg L−1) and the TDFe species are in the following order: Colloidal iron > ionic iron > complexed iron. Compared with the main rivers, the marshy rivers showed higher TDFe concentration and dissolved organic carbon concentration (DOC), and lower pH value. TDFe concentrations were influenced by several factors, whereas, the concentration of DOC, ${\rm HCO}_{3}^{- } $, and ${\rm NO}_{{\rm 3}}^{- } $ showed remarkable correlation through Spearman correlation coefficient analysis. The rivers mostly showed high TDFe concentration on May and October when the farm activities frequently occur. After 50 years' cultivation of wetlands, the free iron (Fe2+ and Fe3+) showed distinct decrease from 195 to 88.2t in Naoli River. Land use change had decreased TDFe output in rivers of Sanjiang Plain because of the changed concentration and component of DOC, which had higher affinity and selectivity with iron.