Distribution Characteristics And Bioavailability Of Organic Phosphorus In Sediments In The Northwestern Part Of Taihu Lake

Biogeochemical cycle of organic phosphorus(OP)from sediments in Taihu is one of key factors of eutrophication in the northwest of Taihu Lake.In this paper,the Ivanoff sequential extraction combined with enzymatic hydrolysis was used to characterize the forms of organic phosphorus from the sediments of river channel,estuary and lake,and explore the factors that affecting the distribution of OP.Furthermore,the laboratory experiment was also conducted to investigate the influence of Vallisneria natans on the distribution of OP.The conclusions based on the article were drawn:(1)The organic pollution is different in different areas and in different inflowing rivers of surface sediments of Taihu Lake,HCl-OP content(>100mg·kg-1)and the ratio of its to TOP content(>0.2)can indicate the degree of organic pollution in the lake.In different areas,the river channel(the content was based on HCl-OP,and>100mg·kg-1),Hongxiang of river estuary and Taige and Zhuhu in the lake;In the typical inflowing rivers,the organic pollution in Taige is more serious than Liangxi,especially Caoqiao river,and the pollution in Wuxi is the lightest.There are obvious differences in the vertical direction of the typical rivers,and we need to focus on:8-12cm of Wuxi estuary(the content of HCl-OP:280.03mg·kg-1,HCl-OP/TOP=0.69),8-12cm of Taige channel(the content of HCl-OP:123.22mg·kg-1,HCl-OP/TOP=0.31),8-12cm of Taige estuary(the content of HCl-OP:154.33mg·kg-1,HCl-OP/TOP=0.31),0-16cm of Taige lake,16-20cm of Liangxi estuary(the content of HC1-OP:116.32mg·kg-1,HCI-OP/TOP=0.44)and 0-16cm of Liangxi lake.Need to focus on monitoring anthropogenic emissions from channel and active sedimentary environment.(2)The release potential of organic phosphorus in different areas of Taihu Lake surface sediments is channel>lake>estuary.The content of EHP:channel(50.30mg·kg-1)>lake(50.30mg·kg-1)?estuary(50.30mg·kg-1),EHP in the lake area is based on monoester phosphorus(30.89mg·kg-1),the content of it is higher than that in estuary(18.29mg·kg-1).The analysis of the content and composition of EHP in different areas show that the high risk of organic phosphorus release:Shedu in channel,Shatang in estuary,Meiliang area and Taige in lake.The content of different forms of EHP is:NaOH-OP>NaHCO3-OP>H2O-OP,there is almost an order of magnitude distance among them.In addition,the main factors influencing OP and EHP in the surface sediments of Taihu Lake are:TOC,OM,sorting coefficient(hydrodynamic)and aquatic plants.OM and TOC play the leading role in affecting TOP and nonlabile organic phosphorus,hydrodynamic influences organic phosphorus organic phosphorus,Humic acid-OP and EHP,and aquatic plants can affect the distribution of diester P.(3)The release potential of organic phosphorus in typical inflowing rivers of Taihu Lake is Taige(the content of EHP:49.58mg·kg-1)>Liangxi(the content of EHP:37.71mg·kg-1)>Wuxi(the content of EHP:15.52mg·kg-1).The content of Wuxi is low(15.52mg·kg-1),so the release risk of organic phosphorus is low;the release risk of OP in Taige lake is high(the content of EHP:66.83mg·kg-1),and the microbial activity of the whole river is low in Taige(the content of diester P<6mg·kg-1);the content of EHP in different areas of Liangxi is similar,and the release risk of OP is the highest at 8-12 cm in lake area,because the labile monoester phosphorus is the main(43.91 mg·kg-1,accounting for EHP ratio of 0.99).In addition,there are significant differences in the release potential of organic phosphorus from sediments in different areas of different layers in Taihu Lake.Wuxi:the microbial activity of 0-8cm in the vertical direction in the Wuxi estuary is high,the release risk of OP at 8-12cm is high(labile monoester phosphorus is the main,the content is 31.84mg·kg-1),and there is almost no EHP in 12-24cm.The release risk of OP is high in 0-8cm of Wuxi lake(so focusing on 4-8cm);Taige:The release risk of OP is high in 0-12cm of channel,16-20cm of estuary and 0-16cm of lake(so focusing on 8-12cm in lake);LXH:the release risk of OP is high in 0-12cm of channel,0-16cm of estuary and 8-12cm of lake,and the microbial activity in the vertical direction of the lake area is very high.The results of Liangxi and Tage were similar.To a certain extent,the above results can provide a reference for the dredging depth.(4)In different growth stages,different components of root layer sediments can affect the forms of OP and EHP.Planting Vallisneria natans can effectively reduce the content of OP and EHP in the sediments(the decrease of the experimental group is significantly larger than that of the control group,and the results are analyzed by single factor analysis of variance.The content of EHP in 30 days and 185 days is significantly different,P<0.05),and the most obvious difference is 5-8cm,among which the main transformation of MOP.5-8cm sediments in the entire growth cycle,Vallisneria natans can significantly reduce the HCl-OP content,and the content of Fulvic acid-OP is significantly decreased in the stable stage of growth(there is significant difference between the experimental group and the control group,P<0.05).The analysis of the content and composition of EHP show that the microbial activity in the sediment is higher at 2-5cm(mainly dominated by diester P);The activities of the microbes are able to transform the labile monoester P of 0-2cm and 5-8cm in 30 days-90 days.The content of EHP is stable(about 23mg·kg-1)in 125 days-185 days,the microbial activity of the root sediments is higher(mainly dominated by diester P).