[Effects of Canalization on the Iron Deposition in Sanjiang Plain].

Canalization is the representative process and landscape of wetland reclamation. A typical ditch system of four levels near the Honghe National Nature Reserve in Sanjiang Plain was selected. Deposition plates were set on the sediments along the ditch level and the remained natural wetland nearby was quantitatively sampled for two years as the control. The deposition fluxes, total iron concentration, iron oxides and their components, as well as biogenic elements in the sediments collected by deposition plates were measured. The results showed that the litter, mud/sand and total deposition fluxes showed no significant differences between different ditch levels, with the means of (57.00 ± 16.90) g x (m2 x a)(-1), (3 997.57 ± 798.98) g x (m2 x a)(-1) and (4054.57 ± 792.91) g x (m2 x a)(-1), respectively. The litter flux decreased with the increase of ditch level, and the flux in the natural wetland [ (120.26 ± 19.42) g x (m2 x a)(-1) ] was significantly greater than that of the ditches. The mud/sand [ (35.41 ± 11.15 ) g x (m2 x a)(-1)] and total deposition fluxes (155.67 ± 20.75) g x ( m2 x a ] were significantly smaller than those of the ditches. There were no significant differences in the total iron between different ditches and natural wetland, while the free iron oxide content in the ditch sediments was significantly lower than that of natural wetland sediment. Except for the main ditch, the amorphous and complex iron oxides in the other ditch and natural wetland sediments showed no significant differences. The free degree of the iron oxide in ditch sediments was 60.2% of that in the natural wetland, while the differences in the complex degree and the activated degree were insignificant. The differences in the total organic carbon, total nitrogen and total phosphorus were insignificant, and all were smaller than those of the natural wetland, with the percentages of 14.6%, 31.6% and 41.0%, respectively. It could be concluded that the effects of canalization on iron and biogenic elements were significant. Consequently, rational agricultural water managements are strongly recommended to avoid the potential environmental and ecological risks caused by canalization in Sanjiang Plain.