Study On The Transport Pathway And Source Tracing Of Phosphorus In A Typical Lake And Small Watershe

Cyanobacteria blooms have become an urgent environmental problem around the world.Phosphorus（P）significantly restricts phytoplankton metabolism,and high concentration of phosphorus is easy to cause water eutrophication.The distribution and management of phosphorus sources are increasingly difficult due to the complex transport and transformation processes of phosphorus in lake ecosystems.In this paper,³¹P NMR and chemical extraction techniques were used to characterize and quantify phosphorus components in soil,estuarine sediments,pond sediments and lake sediments of Shijiuhu Lake Basin to investigate the transport and migration process of phosphorus at basin scale.On this basis,combining with mineralogical analysis,the phosphate oxygen isotope(δ¹⁸O_P)of resin-extractable phosphorus samples from diverse land-use patterns in Shijihu Basin was investigated.The main conclusions are as follows:（1）The mean value of TP in the basin:pond>lake>soil>estuary;Mean of Po:lake>soil>estuary>pond;The contents of phosphorus in the sediments of lake center are HA-Po>FA-Po>Res-Po>Biomass-Po>HCl-Po.The contents of phosphorus in estuarine sediments are as follows:FA-Po>HA-Po>Res-Po>HCl-Po>Biomass-Po;APA mean values are:soil>lake>estuary>pond,soil had the highest Po activity,and lakes had the highest Vmax/Km and the highest mineralization efficiency.（2）³¹PNMR was used to determine the chemical composition of Po and to analyze the migration and transformation process of Po.The main sources of organophosphorus in the basin are farm Land soil and aquaculture pond disturbed by human.Tributaries connected to lakes degrade HCl-Po from farm fields and aquaculture ponds into FA-Po,which will deposite in estuaries.In the process of resuspension,FA-Po decomposed and released active phosphorus by microorganisms.The Po of lake sediments mainly comes from the remains of algae organisms inside the lake.（3）The results showed thatδ¹⁸O_P values ranged from+15.23 to+21.92‰in agricultural soil,+16.53 to+24.10‰in estuary sediments,+18.90 to+20.90‰in pond sediments,and+17.42 to+19.70‰in lake sediments.Isotopic signa-tures indicated that chemical fertilizers with heavierδ¹⁸O_P values（+20.70～+26.50‰）were the predominant contributors of P in the soil.（4）The river transportation together with Fe/Al–P desorption on anaerobic condition simultaneously stimulated the enrichment of P in the lake sediments,even though the biotic activity regulated the isotope values moving toward the equilibrium.Eroded soil was the important source of P in lake and pond sediments via drainage and runoff,and conserved the source isotope signal in the samples.Stronger biotic activity in the aquatic environments draggedδ¹⁸O_P values toward the equilibrium.However,conspicuous off-equilibrium isotope signature suggested the terrestrial sources in the aquatic ecosystems.The calculation of two end-member linear mixing models suggested that soils also predominantly controlled the P occurrence in the lake sediments with contribution higher than 80%,indicating that decreasing inputs from the agricultural activities is important in P reduction on catchment scale.Generally,δ¹⁸O_P from different sources can provide indirect and important evidences for the identification and management of P sources in the lake catchment.