Microbial Effecting Mechanism Of Interface Coupling Behavior Of Phosphorus And Iron Based On Microcosm System

As one of the main driving factors during the early diagenesis of organic matter?OM?,iron redox reaction is identified as the main kinetic mechanism affecting phosphorus migration and transformation,especially the dissimilatory Fe?III?reduction droven by microorganism in anaerobic environment.In this disseratation,the microcosm system of“overlying water-pore water-sediment core”was established to investigate the effect of iron dissimilation reduction on phosphorus regeneration cycle driven by different microbial species during different seasons.The synchronous changes of active iron(Fe²⁺),total iron?Fe_T?,inorganic phosphorus?IP?and total phosphorus?TP?in different systems were monitored to understand the different characteristics of biogeochemical dynamics across the water-sediment interface during the frozen and non-frozen periods,especially the effects of the interface process on the environmental behaviors of nutrients and pollutants during the frozen period.Meanwhile,the different interface behavior of phosphorus and iron along with the changing redox gradient zones were discussed according to the effects of different microbial species.This work is of great significance to enrich the controling mechanism of inter P loading droven by iron oxides during the variation of redox boundary layer coulpling with seasonal change in lake sediments in cold and dry regions.The main results and conclusions are as follows:1.The concentrations of phosphorus in the overlying water of the microbial addition group were higher than those of the control groups in both non-frozen and frozen period.In the early stage of culture,the dissimilatory Fe?III?reduction and the degradation of organic phosphorus?OP?were stronger due to the higher microbial metabolic activity,which leading to an increase trend of IP release from sediments to overlying water.2.The microcosm experiments showed that a concentration-dependent response of IP with Fe²⁺was found in the overlying water-pore water-sediment system,indicating that the behavior and changes of the elements in sediments would significantly correspond to the hydrochemical characteristics of the overlying water through the bridging effect of pore water.3.During the non-frozen period,a simultaneous releaseing trend of iron and phosphorus was found under the effect of the four strains,indicating that the microbial activity was high.There were different mechanisms such as enzymatic reduction,reduction with Fe?III?oxides as electron acceptors and reduction of metabolic products promoting the release of iron-bound phosphorus in sediments.4.The simultaneous release trends of iron and phosphorus were observed not in all microbial addition groups due to the limited metabolic activity during the frozen period.The releasing P in nitrate reducing bacteria addition groups was attributed to the degradation of OM and OP,while it associated with the reductive dissolusion of P boud to iron oxides in the groups of iron reducing bacteria and others bacterias additions.It suggested that the releasing P was generated from different source or binding fractions depending on the microorganisms species and environment conditions.5.The results showed that the release potential of phosphorus in the iron reduction zone?8-10 cm?in the sediment profile was greater,which could be called a hot-spot layer of phosphorus release,corresponding to the nutrient levels in the pore and overlying water.It also had an important guiding role in the accurate determination of the depth for lake sediment dredging.6.Although the microbial activity was limited during the frozen period,the release of internal P loading still had a non-negligible effect on the nutrients supplying and sustaining in the water column.The phosphorus released from sediments was concentrated in the thining water column below the ice layer,providing the key nutrient supply at the start-up stage of algae flourishing in spring and summer.