Effects Of Exogenous Input On Phosphorus Regeneration And Tranfer In Newborn Surface Layer By Sediment Dredging

The effect of external pollution input on phosphorus regeneration,transport and transformation in newborn surface layer by sediment dredging is still unclear.It is significant to clarify this issue for the control and management of external pollution loading at the watershed scale after the implementation of sediment dredging.In this study,sediments in Meiliang Bay of Lake Taihu were taken as the research object.In-situ dredging simulation in lake was used to study the transport and transformation of phosphorus at the sediment-water interface before and after dredging under the condition of external or non-external particulate matter input,and to explore the control effect of dredging on phosphorus release of internal loading.We reached the following conclusions:?1?The continuous accumulation of particulate matter increases the water content and porosity of surface sediments.Dredging reduces the LOI,TP and TN content of surface sediments,but the continuous accumulation of particulate matter leads to a large increase in surface content.TP content of undredged and dredged column samples in the exogenous group was 1.5 and 1.6 times of that in the non-exogenous group,while TN content was 1.8 and 1.6 times of that in the non-exogenous group.The continuous accumulation of particulate matter aggravates sediments pollution status.External input reduces the effects of dredging measures.?2?The oxygen content of sediment-water interface between the dredged group and the undredged group without external particulate matter input reach 9.0mg·L^-1and 8.3mg·L^-1,and the oxygen permeation depth was also as high as 8.8mm and6.8mm,significantly higher than that of exogenous groups.Dredging and blocking the input of external particulate matter can both improve the redox condition of sediments to a certain extent.?3?Dredging and blocking the input of external particulate matter have a positive effect on the control of Mobile-P content in surface sediments,which weakens the exchange effect of Mobile-P with interstitial water and the possibility of migration to the overlying water;In sediments Fe-p has a tendency to transform to Ca-P.In the non-external particulate matter input group,Org-P in surface sediments of dredged and undredged column samples was significantly negatively correlated with Ca-P and Al-P in dredged and respectively there is a possibility that Org-P will be converted to Ca-P and Al-P.Under the condition of blocking the input of external particulate matter,it is more conducive to the conversion of potentially Mobile-P to a more stable and difficult-to-release phosphorus.?4?The EPC₀ of suspended particulate matter is significantly higher than other groups,the concentration ranges from 0.036 to 0.160mg·L^-1,the concentration of dredged group without external particulate matter input ranges from 0.017 to0.040mg·L^-1.The dredging measures and the prevention of external input can effectively reduce the sediment EPC₀ to a certain extent,and have a better weakening effect on the EPC₀ release risk of the upward water body.With the development of the experiment,the ion replenishment capacity of sediments has changed from non-buffer type to partial buffer type,and the enhancement of this ability is more significant in the exogenous group.Dredging enhances the retention capacity of phosphorus in sediments and the dynamic response between sediments and pore water,and effectively weakens the release potential of phosphorus from sediments.?5?The concentration of PO₄^3--P in pore water of undredged column without external particulate matter input group,undredged and dredged column with external particulate matter input groups range from 0.16 to 1.81mg·L^-1,0.13 to 1.44mg·L^-1 and0.11 to 1.27mg·L^-1.Dredged column with external particulate matter input group ranges from 0.11 to 0.46mg·L^-1,which maintains a low concentration during the experiment.The DRP concentration of pore water in undredged and dredged column with external particulate matter input groups reach 1.01mg·L^-1 and 0.35mg·L^-1 at8mm below sediment-and-water interface.?6?The sediments have undergone two source-sink transitions in a year.During the winter and spring,the sediments changed from the sink to the source to the overlying water.In the non-external input group,the sediments in the summer and autumn changed from the source to the sink.The phenomenon occurs in the external input group in autumn and winter.External particulate matter input prolongs the time of phosphorus release from sediment to overlying water for about 2 months.Dredging measures reduce the release flux of endogenous phosphorus in the sediment,which can effectively control the release of endogenous phosphorus.Cutting off the input of external particulate matter plays a good role in promoting the control of internal phosphorus loading by dredging.In summary,the accumulation of contaminated particulate matter in the lake after dredging will result in a rapid recovery of sediment contamination after dredging.If these pollutants cannot be effectively controlled,dredging will be difficult to achieve long-term endogenous pollution control effects.Therefore,the combined pollution status and settlement of these particles must be studied before dredging to determine whether dredging and corresponding pollution recovery control measures can be carried out.