三江平原河水中铁的形态研究

采集三江平原河流(主要河流和沼泽性河流)水体,利用切向超滤和玻璃纤维滤膜技术分离铁的形态,研究了三江平原河水中铁的含量、形态和潜在络合竞争能力,以揭示湿地开垦对铁形态和输出通量的影响.结果表明,含有丰富有机质的典型沼泽性河流中可溶铁和酸性不稳定铁平均含量高达1.16和0.81 mg.L-1,是主要河流铁的重要补给来源,主要输送络合态铁(占可溶铁70.9%)和离子态铁(占可溶铁9.3%).河流中可溶态铁均以低分子量铁为主要迁移形态,在主要河流中低分子量铁占可溶态铁的68.7%,含量为0.13 mg.L-1,在典型沼泽性河流中占可溶态铁的82.2%,含量为0.88 mg.L-1;典型性河流中Fe3+含量是主要河流的3.1倍,Fe2+含量相差不大.通过菲咯嗪的配位竞争实验发现,络合态和胶体态铁中也存在Fe(Ⅱ)的结合形态;在典型沼泽性河流中,络合态铁具有更高的潜在络合竞争能力,更容易形成稳定不易分解的络合态铁.因此,三江平原湿地开垦导致沼泽性河流铁输出的减少,稳定络合态铁输出的减少直接影响铁的迁移距离,对近海铁的输送产生巨大影响.

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.