Storage Capacity And Influencing Factors Of Organic Phosphorus In Restored Wetlands Of The Yellow River Delta

As an important fraction of soil phosphorus,organic phosphorus plays an important role in the supply of soil bioavailable phosphorus and adjacent water eutrophication.Coastal wetland can store organic phosphorus,and formed the last barrier to prevent organic phosphorus from flowing into offshore water body.Soil organic phosphorus storage capacity（SP_oSC）is a measure to assess soil organic phosphorus storage capacity and loss risk from soil.In this study,the maximum sorption capacity(Q_max)of soil organic phosphorus in the Yellow River Delta was fitted by isothermal adsorption experiment,and the degree of organic phosphorus saturation（DP_oS）and SP_oSC were further determined.The effects of vegetation variation,growth period,soil profile depth and wetland restoration on the SP_oSC were explored.Furthermore,the preservation of organic phosphorus during wetland restoration was evaluated.The specific results are as follows:1.Using the different land uses soil in the Yellow River Delta,the SP_oSC was studied with the example organic phosphorus such as phytate,sodium-β-glycerophosphate（β-G-P）and adenosine disodium triphosphate（ATP）.The results showed that the threshold value of DP_oS for phytate,β-G-P and ATP were0.64%,0.53%and 1.39%,respectively.Based on this change point,the SP_oSC in the Yellow River Delta is calculated as follows:SP_oSC=（0.64%-DP_oS）×(21.194SOM+0.131Ca _M3+2.684Al_ox+0.085Ca CO₃-1.281Fe_ox),SP_oSC=（0.53%-DP_oS）×(13.469SOM+0.167Ca _M3+4.357Al_ox),SP_oSC=（1.39%-DP_oS）×(11.993SOM+0.098Ca _M3+1.530Al_ox).The SP_oSC for the three example organic phosphorus in restored wetlands were-842.24～533.42 mmol/kg,-852.43～426.30 mmol/kg,and-904.62～332.62 mmol/kg,respectively.The results indicated that the restored wetland act as the“highland”for the preservation of organic phosphorus of the Yellow River Delta.We recommended to fully use the restored wetland to decrease the organic phosphorus pollution in the watershed from upland to offshore.2.The SP_oSC in Yellow River Delta is significantly affected by wetland restoration,vegetation type,plant growth period and soil depth.With the implementation of wetland restoration,the restored wetlands have proven to be effective at increasing the vegetation community,and increasing the soil organic matter content and the SP_oSC value.The plant growth also improved the storage of organic phosphorus through the improvement of soil organic matter content.Organic phosphorus was mainly stored in the surface soil（0-5cm）of the restored wetland.3.There was a significant positive correlation between SP_oSC and the concentration of Fe_ox,Al_ox,Mg,Ca,p H,TOC,and as well as the percentage of clay particles in the sample（P<0.01）.In the restored wetland,the moderately available organic phosphorus contributed more than 62%of total organic phosphorus in the Yellow River Delta.In generally,the restored wetland act as the“highland”for the preservation of organic phosphorus of the Yellow River Delta.We fully recommended to use the restored wetland to reduce the upstream P pollution to the offshore environment of the Bohai Sea,and thus achieve a sustainable P balance in the land-wetland-offshore basin.Our results provided the basic data for wetland protection and management in the future.