How do inundation provoke the release of phosphorus in soil-originated sediment due to nitrogen reduction after reclaiming lake from polder

Different N and P fractions inmicrocosm incubation experiment was measured using highresolution in-situ Peeper and DGT techniques combining with sequential extraction procedure.The results showed the synchronous desorption and release of PO_(4)^(3-),S^(2-)and Fe^(2+)from the solid soil-originated sediment.This trend indicated that the significant reduction of Fe-P and SO_(4)^(2-) occurred in the pore water during the inundation.The concentrations of PO_(4)^(3-) in the overlying water and pore water increased to more than 0.1 and 0.2 mg/L at the beginning of the incubation experiment.Decreased NO_(3)^(-) concentrations from more than 1.5 mg/L to less than 0.5 mg/L combining with increasing NH^(4+) concentrations from less than 1mg/L tomore than 5 mg/L suggested the remarkable NO_(3)-reduction via dissimilatory nitrate reduction to ammonia(DNRA)pathway over time.High NH^(4+) concentrations in the pore water aggravated the release of Fe^(2+) through reduction of Fe(Ⅲ)-P as electric acceptors under anaerobic conditions.This process further stimulated the remarkable releasing of labile PO_(4)^(3-) from the solid phase to the solution and potential diffusion into overlying water.Additionally,high S^(2-) concentration at deeper layer indicated the reduction and releasing of S^(2-)from oxidation states,which can stimulated the NO_(3)^(-)reduction and the accumulation of NH^(4+)in the pore water.This process can also provoke the reduction of Fe-P as electric acceptors following the release of labile PO_(4)^(3-)into pore water.Generally,inundation potentially facilitate the desorption of labile P and attention should be paid during the reclaiming lake from polder.

Impacts of ecological restoration projects on agricultural productivity in China

The changes in cropland quantity and quality due to land use are critical concerns to national food security, particularly for China. Despite the significant ecological effects, the ecological restoration program （ERP）, started from 1999, has evidently altered the spatial patterns of China＇s cropland and agricultural productivity. Based on cropland dynamic data from 2000 to 2008 primarily derived from satellite images with a 30-m resolution and satel- lite-based net primary productivity models, we identified the impacts on agricultural produc- tivity caused by ERP, including ＂Grain for Green＂ Program （GFGP） and ＂Reclaimed Cropland to Lake＂ （RCTL） Program. Our results indicated that the agricultural productivity lost with a rate of 132.67×104 t/a due to ERP, which accounted for 44.01% of the total loss rate caused by land use changes during 2000-2005. During 2005-2008, the loss rate due to ERP de- creased to 77.18×104 t/a, which was equivalent to 58.17% of that in the first five years and 30.22% of the total loss rate caused by land use changes. The agricultural productivity loss from 2000-2008 caused by ERP was more attributed to GFGP （about 70%） than RCTL. Al- though ERP had a certain influence on cropland productivity during 2000-2008, its effect was still much less than that of urbanization; moreover, ERP was already converted from the project implementation phase to the consolidation phase.