| The temporal-spatial trends of soil total iron concentration (Fet), free degree (Fed/Fet), activation degree (Feo/Fed) and complex degree (Fep/Fed) of soil iron oxides after reclamation were studied in Sanjiang Plain Wetlands. The result suggests that Fet in the upper tillage layers (0～20 cm) are influenced by reclamation more significantly than that in the lower ones (20～100 cm), and so does the early ages (0～1 years) than the late ages (1～25 years). Fet is negatively correlated with organic matter extremely significantly (R=-0.62), while that with total phosphorus and pH are not significant. Fet of soil layer Ⅰ (0～10 cm) increases obviously during the first 7 years after reclamation, and tends to become stable after 13 years, while those ages of soil layer Ⅱ (10～20 cm) are 8 years and 15 years respectively. Soil layer Ⅰ shows shorter responding time and better regularity than layer Ⅱ. Fed/Fet increases rapidly after reclamation, decreases later and then increases again. Feo/Fed indicates exponential decrease with the reclamation ages as well as Fep/Fed. Feo/Fed of layer Ⅰ decreases radically during the first 4 years after reclamation and tends to become stable after 13 years, while that of layer Ⅱ decreases dramatically within the first year and keeps stable henceforth. The counterparts of Fep/Fed are 6 years, 14 years, and 2 years respectively. With the fitted experimental equations of Fet, Feo/Fed, and Fep/Fed, the ages of reclamation can be deduced reversely, which indicates the implication of iron on the shifts of soil environment. |
