Abstract: The distribution and transformation of iron in estuarine soil plays an important role in wetland nutrient cycling and organic pollutant degradation. To explore the distribution characteristics of iron in estuarine soil under fossil oil pollution can provide a reference for understanding the distribution of petroleum hydrocarbons and iron transport and transformation in estuarine wetlands. Soil samples were collected from natural wetlands of Liaohe River estuary and wetlands around fossil oil wells with different exploitation years, and then were measured for total petroleum hydrocarbon (TPH), total organic matter (TOC), Eh, pH, total iron (Fe_t), acid soluble Fe²⁺, Fe³⁺, free iron oxide (Fe_d) and amorphous iron (Fe_o). The results showed that: (1) The petroleum hydrocarbon content of the surface soil layer around the oil well with an exploitation age of 10 years was significantly higher than that of the other layer soils. More petroleum hydrocarbon was accumulated in the 20-30 cm soil layer around oil wells with an exploitation age of more than 10 years, and oil pollution facilitated the increase of total organic matter content and pH in soil. (2) There were positive correlations between petroleum hydrocarbon and soil organic matter (P<0.01), and between soil organic matter and soil Fe²⁺ (P<0.05). (3) In natural wetland, soil Fe²⁺ content increased with soil depth, while in oil-contaminated soil, the Fe²⁺ content of upper soil layer (0-30 cm) was relatively higher, and soil oxidation gradually decreased with increasing soil depth. The distribution of soil Fe_d was affected by Fe_t. The invasion of petroleum hydrocarbon enhanced Fe_d production. There was no significant difference in the distribution of Fe_o in soil with different mining years.

Key words: petroleum hydrocarbon, Fe, wetland, soil.