[Research on iron in marshy rivers of the Sanjiang Plain].

River waters (including the main river and marshy river) were sampled to study the iron concentration, species and complexed competitive ability in the Sanjiang Plain in order to reveal the influence of wetland reclamation on the iron species and output flux. The cross-flow filtration technique was employed to separate iron species according to size fraction. The result showed that the typical marshy river which is rich in organic matters became an important iron source for atypical marshy river. In the typical marshy river, the concentration of total dissolved and acid-labile iron reached to 1.16 and 0.81 mg x L(-1), respectively. Complexed (accounting 70.9% of total dissolved iron) and ion iron (accounting 9.3% of total dissolved iron) were the primary species in dissolved iron. Therefore, iron transported primarily as low-molecular-weight iron forms in river waters in the Sanjiang Plain. The low-molecular-weight iron accounted for 68.7% and 82.2% of total dissolved iron and low-molecular-weight iron concentrations reached to 0.13 and 0.88 mg x L(-1) in the main and typical marshy river, respectively. The ferric iron concentration in the typical marshy river was 3.1 times higher than that in the atypical marshy river. Little difference of ferrous iron contents between the typical and atypical marshy river was observed. Fe(II) was found in complexed and colloidal iron through ligand competitive experiment. In the typical marshy river, complexed iron had a higher ligand competitive ability, which could form more stable complexed iron. The decline of the stable complexed iron output flux due to reclamation of the Sanjiang wetland would greatly influence the distance of iron transportation, especially iron output to the coastal waters.