Characteristics Of Iron-Bound Phosphorus In Sediments Of Lake Honghu Mediated By Exogenous Nitrogen And Plant Action

Phosphorus is a key factor affecting the nutritional level of lakes.In the case of decreasing exogenous phosphorus input,the release of endogenous phosphorus caused by sediments is an important cause of lake eutrophication.There is a close relationship between iron-bound phosphorus and phosphorus migration in sediments.Due to the continuous exogenous nitrogen input and aquatic plants on lake habitats,clarifying their effects on the transformation of iron-bound phosphorus would be helpful to better understand the geochemical cycle of phosphorus.In this study,simulation system was carried out with sediment-overlying water from Lake Honghu to explore the transformation of phosphorus in the system and the variation characteristics of iron-bound phosphorus in sediments under the conditions of different exogenous nitrogen.In addition,the response characteristics of ferrous phosphorus transformation to nitrate-dependent Fe（II）oxidation bacteria（NDFOB）and plant secretion were investigated with NDFOB culture system.The main results were as follows:（1）In the sediment-overlying water simulation system,after 60 days of culture,higher concentrations of TP and PO₄^3-in the overlying water of the NO₃^--input group were found than the CK group and the NH₄⁺-input group.Microbial community analysis showed that the input of NO₃^-and NH₄⁺increased microbial diversity,and the input of NO₃^-increased the relative abundance of Proteobacteria by 1.57%.Iron-bound phosphorus accounted for a high percentage of phosphorus content（about 30%）.The input of NO₃^-and NH₄⁺reduced the content of iron-bound phosphorus,and the decrease of ferrous phosphorus content in the two groups was more obvious,which was 32.64%and 68.53%lower than CK respectively on the 60th day.The determination of diffusive gradients in thin-films technique（DGT）showed that the concentration of labile phosphorus in sediments increased with the increase of depth,and the NO₃^-input promoted the concentration of labile Fe（II）in pore water.（2）Compared with the sediment-overlying water system planted with Eichhornia crassipes,the sediment planted with Myriophyllum verticillatum had a better’sink’effect on the phosphorus in the overlying water,and the iron-bound phosphorus in the sediment increased remarkably with the process,accounting for more than 40%of the total phosphorus content.The iron-bound phosphorus content in the sediment near the root of Myriophyllum verticillatum was higher than that far from the root.Ferrous phosphorus illustrated a similar increasing trend as iron-bound phosphorus along with time,which was 24.87%～43.52%higher than the original content on the 60th day of culture.Due to more phosphorus was fixed to the sediment solid phase,the content of labile phosphorus in the water phase decreased correspondingly.The average concentration of labile phosphorus in the sediments planted with Eichhornia crassipes and Myriophyllum verticillatum on the 60th day of culture was 76.50%and 60.91%lower than the original concentration,respectively.The number of NDFOB in the sediments planted with Myriophyllum verticillatum was higher than that in the sediments planted with Eichhornia crassipes.（3）In absent of NDOFB effect,it was found by XRD characterization that vivianite could be maintained in good integrity.In the culture system of Paracoccus denitrificans as NDFOB model bacteria,the root secretion of Myriophyllum verticillatum reduced the intensity of peak diffraction of weakly crystallized vivianite,but had little effect on strongly crystallized vivianite.The capacity of weakly crystallized vivianite promoting the utilization of humic-like organic matter in the solution of root secretion by Paracoccus denitrificans was higher than the strongly crystallized vivianite,which reduced the relative proportion of humic-like organic matter by 6.45%.The effect of root secretion on different groups in ferrous phosphate minerals was not obvious in the culture system.