The effect of water regime on the spatial distribution of total iron and the seasonal variation of dissolved iron in a typical annular wetland of Sanjiang Plain, Northeast China, was analyzed through in situ sampling of soils and soil solutions. The results showed that the average level of total iron of the wetland soil (0-60 cm) was (2.54 +/- 0.73) x 10(4) mg x kg(-1), which decreased gradually from the Calamagrostis angustifolia community in the edge of the annular wetland [(2.91 +/- 0.51) x 10(4) mg x kg(-1)], to the C. meyeriana community [(2.60 +/- 0.35) x 10(4) mg x kg(-1)], the C. lasiocarpa community [(2.48 +/- 0.31) x 10(4) mg x kg(-1)], and the of C. pseudocuraica community [(2.17 +/- 0.31) x 10(4) mg x kg(-1)] in the centre of the annular wetland. The iron solubility of perennial flooding soil was higher than seasonal flooding soil. The gross dissolved iron increased from soil thawing in the late spring [(0.35 +/- 0.086) mg x L(-1)] to freezing in the late autumn [(12.67 +/- 2.92) mg x L(-1)], because the soil iron was activated by continuous submergence. The reduced degree as shown by Fe3+/Fe2+ increased with the increment of water depth or flooding duration. Significant and extremely significant correlations were observed between dissolved Fe3+ or Fe2+ and pH, TOC, TN and PO4(3-), which suggested that the distribution of iron was influenced by the soil physical and chemical properties, and coupled with the transfer and transformation of C, N, and P elements.