Bioavailability Of Sediment Phosphorus In Dianchi Lake,Southwest China

Eutrophication is one of the most serious water environment problems in the world,while phosphorus?P?is the key limiting factor of water eutrophication.At present,the research on the origin,migration and transformation mechanism and bioavailability of P in aquatic ecosystem is still very scarce.In recent years,oxygen isotopes of phosphate??18O_p?,as a novel and potential tool,has been applied to identify P sources and its migration and transformation mechanisms in water bodies?including oceans,rivers and lakes?,soils and sediments,which have made a breakthrough.In this paper,Dianchi Lake,as a classically eutrophic lake,is selected as the research object.The pretreatment processes of?¹⁸O_pin environmental samples?soils and sediments?were modified and improved.On this basis,the?¹⁸O_pcompositions of the sediments from Dianchi Lake and the samples from different phosphorus sources in the basin were studied.Furthermore,with the aid of ³¹P-NMR and enzymatic hydrolysis,the composition of organic phosphorus?P_o?and its bioavailability in Dianchi Lake sediments were detected.The main conclusions are as follows:The pretreatment procedure of?¹⁸O_pin soil and sediment samples were modified and improved.The improved pre-treatment method is more simple,and significantly improves the sample recovery and impurity removal efficiency.The bioavailability of inorganic P?including H₂O-P,Na HCO₃-P and Na OH-P?in Dianchi Lake sediments ranged from 506.5 mg·kg^-1to 1549.6 mg·kg^-1,which accounted for 32.6%-58.8%of the total phosphorus?mean:41.7%?that indicated a high bioavailability of inorganic P in Dianchi Lake sediments.The values of?¹⁸O_pof different forms of P in Dianchi Lake sediments are ranked as follows:?¹⁸O_p?Na HCO₃?>?¹⁸O_p?Na OH?>?¹⁸O_p?HCl?.The?¹⁸O_pvalues of different P source samples are remarkably different from those of sediment,which shows that the phosphorus in Dianchi Lake sediment has undergone strong biological transformation and produced significantly isotopic fractionation.In this case,?¹⁸O_pis not suitable for the source discrimination of P in Dianchi Lake.The values of?¹⁸O_Pextracted by Na HCO₃and Na OH in north of Dianchi Lake sediments with larger algal biomass were significantly higher than those in the south lake area with relatively smaller algal biomass.These results provide a potential new perspective for the study of bioavailability and efficiency of water and sediment P in Dianchi Lake using?¹⁸O_ptechnology.The composition of P_oin Dianchi Lake sediments mainly included phosphate monoester,phosphodiester,phosphonate,pyrophosphate,polyphosphate.The amount of Na OH-P_ohydrolyzable under alkaline phosphatase condition can account for 30% of Na OH-P_o.The amount of Na OH-P_ohydrolyzable under alkaline phosphatase and phosphodiesterase can account for 50%of Na OH-P_o.The results indicated that the sedimentary P_ohave high activity under the condition of enzymes in Dianchi Lake,which may be an important P source to induce algal blooms.The combination with?¹⁸O_p,enzymatic hydrolysis and ³¹P-NMR are expected to be important tools for quantitative study of P?especially P_o?migration and transformation mechanism,biological utilization efficiency and pathway in eutrophication lakes.