The Effect Of The Key Factors On The Phosphorus Behavior Of The Sediment Surface In Taihu Lake

In the process of the development and utilization of lakes, excessive nutrients enter the surface water. Thiscauses heavy or middle eutrophication in most of the lakes, and algal blooming phenomenon happensfrequently. Phosphorus is the key limiting factor of lake eutrophication. With the reduction and control of theexogenous phosphorus, the release of endogenous phosphorus has become an important source of phosphorus,and there is no effective engineered measure to decrease the contamination from endogenous phosphorus. Thisthesis studied the potential release of phosphorus from sediment in different sites in Taihu, and chose thesediment sample with the strongest phosphorus release to investigate the effect of different environmentalfactors,different forms of iron, organic matters, electron acceptors, and their complex function on the behaviorof phosphorus in sediments. Main experimental results were illustrated as following:The sediment sample from Xiao meikou, among sediments taken from the nine sampling points in TaihuLake, was found to have the greatest potential of the phosphorus release. The sediment sample in Xiao meikouwas abundant of organic matter and phosphorus.In the condition of anaerobic and no disturbance, phosphorus released from sediments to the overlyingwater, and alternative aerobic-anaerobic conditions was more conducive to such a release; conversely, underaerobic and no disturbance conditions, phosphorus would go back to sediments. pH was an important factor toaffect the release of phosphorous, and alkaline condition led to the phosphorus release from the sediment. Inaddition, the period which was needed to reach the maximum phosphorus release depended on pH values. Themore alkaline for pH was, the sooner the maximum phosphorus release reached. Alkaline and aerobicconditions promoted the release of NaOH-P, and anaerobic and alkaline conditions did help the release ofNH4-P. However, the alkaline condition was not conducive to the release of Fe-P and Al-P.Release of phosphorus from sediment increased with increasing temperature from33°C to40°C, andadding organic matter was conducive to this release. Effect of iron oxide(FeOOH) addition to sediments onthe phosphorus release was some complex. In the aerobic condition, FeOOH adsorbed phosphorus obviously,making the TP of the overlying water close to zero in six days. Under the anaerobic condition, however, ironaddition could only restrain to some constent but not stop the phosphorus release on the whole. Different formsof iron played different roles in the phosphorus release from sediment. Nano-goethite was easy to be utilized byiron-reducing bacteria for growth, and enhanced microbial iron reduction. Therefore, amendation ofnano-goethite promoted the phosphorus release.Adding SO₄^2- could significantly promote the release of phosphorus from sediments. Among glucose,acetate sodium, cellulose and algae, acetate sodium had the best performence on promoting the release ofphosphorus from sediments.In the comprehensive effects of phosphorus release, the sulfur reducing and iron reducing processes werecompetitive, and the sulfur reduction happened prior to the iron reduction. The existence of organic matter promoted these microbial reactions, and the number of the sulfur-reducing and iron-reducing bacteria wasalmost similar when the enough carbon resource was provided. In the process of these two types of reducing,there would be more Fe-S compounds in the sediment, making the PO₄^3- which was bound to iron release to theoverlying water.