Effects Of Lanthanum Modified Bentonite On The Overlying Water Phosphorus And The Sediment Phosphorus Forms Concentrations In Eutrophic Shallow Lakes

Lanthanum modified bentonite is increasingly used worldwide to control sediment phosphorus（P）release and improve water quality.In this paper,we studied the application of Lanthanum modified bentonite in South Lake in Jinan University（JNU）,Guangdong and Yanglan Lake in Hubei,to explore effects of lanthanum modified bentonite on tphosphorus forms in the overlying water and the sediment.The mass ratio of the quality of the lanthanum modified bentonite and the sum of the P_mobile in the surface 5 cm of the sediment and the TP of overlying water was 100:1 in JNU South Lake,about 590 g/m².Yanglan Lake added the lanthanum modified bentonite with a dose of 500 g/m²,and added polyaluminium chloride with a dose of50 g/m² at the same time.This study monitored sediment phosphorus form concentration in the JNU South lake and Yanglan Lake（about 2 months before and after the restoration）,and monitored the water quality parameters such as phosphorus concentration,suspended solids,chlorophyll a and transparency during the restoration period.It also analyze that metal content of sediment before and after application of lanthanum modified bentonite in Yanglan Lake.The results of JNU South Lake experiment showed that the phosphorus concentration tended to decrease,but fluctuated greatly after treatment.To 60 d,the TP,PP,DTP and SRP concentration decreased by 45.21%,43.91%,47.79%and45.21%respectively.The labile-P（NH₄Cl-P）and reductant-soluble-P（BD-P）contents decreased andmore stable apatite-P（HCl-P）and residual-P（Ref-P）contents increased after treatment,but metal-oxide-P（Na OH-RP）and organic-P（Org-P）contents had no changes.These findings indicate that lanthanum modified bentonite can change sediment phosphorus forms and make potentially releasable sediment phosphorus forms to residual forms after treatment,and thus it can inhibit the release of the sediment phosphorus.At the same time,lanthanum modified bentonite can reduce the phosphorus content in lake water,and thus improve water quality.The results of Yanglan Lake study showed that the combination lanthanum modified bentonite and Polyaluminium chloride（PAC）can reduce the concentration of suspended solids,the concentration of chlorophyll a and the concentration of phosphorus,and increase the transparency rapidly,and thus water quality has been significantly improved.At the end of the experiment（24 October）,TP,PP and SRP concentrations decreased by 89.53%,71.40%and 93.41%respectively.The content of La in the restoration area increased significantly in the top 8 cm of the sediment.After lanthanum modified bentonite and PAC applicaton in Yanglan Lake,easily released NH₄Cl-P,BD-P and Org-P contents in the sediments decreased and stable HCl-P and Ref-P contents increased,thus the phosphorus retention capacity of sediments increased and and the release risk of sediment phosphorus decreased.