Effect Of Outbreak And Extinction Of Algal Blooms On Organic Matter And Phosphorus In Water And Sediment Of Lake Taihu

Algal bloom is common in lakes and reservoirs in many countries and regions.Its growth and extinction will affect the physical and chemical properties of water and sediment,and further affect the characteristics of organic matter and phosphorus in water and sediment.Meanwhile,the changes of organic matter and phosphorus will also affect the growth of algae,which is the main reason for the vicious cycle of algal blooms.In this paper,Zhushan Bay and Meiliang Bay,which are two regions of Lake Taihu with severe algal bloom,were studied.Samples of water and sediments were collected from June 2016 to October 2016?once a month?.The contents and composition characteristics of organic matter and phosphorus in water and sediments of Lake Taihu were analyzed.Diffusive Gradientsin Thin-films?DGT?was used to characterize variation in the migration rate of phosphorus at sediment-water interface,then combined the physical and chemical properties of water and sediments,the effects of outbreak and extinction of algal bloom were explored on the characteristics of organic matter and phosphorus in water and sediments.The main results were as follows:1.From June to October,the change trend of dissolved organic matter?DOM?in the overlying water of Zhushan Bay and Meiliang Bay was the same as that in the surface interstitial water,and the content of DOM in the surface interstitial water was higher than that in the overlying water.In August,the content of DOM in interstitial water was lower than that in other months.From August to October,the content of DOM in interstitial water increased gradually.From June to August,the content of various forms of phosphorus in the overlying water increased obviously.The content of total dissolved phosphorus?TDP?and phosphate(PO₄^3-)reached the maximum in August,but TDP/TP%,PO₄^3-/TP%was lower.With the decline of algae,the proportion increased gradually from August to October.2.From June to October,the change trend of total organic matter?TOM?,labile organic matter?LOM?and DOM)content in sediments of Zhushan Bay and Meiliang Bay was probably"W".Their contents in June,August and October were higher than those in July and September.They had significant negative correlation with pH,and a significant positive correlation with water content.There was a strong positive correlation between TOM,DOM and LOM in sediments.From June to August,the contents of light organic matter,mobile humic acid?MHA?and calcium humic acid?CaHA?in sediments were higher than those in September and October.3.The results of SMT determination indicated that inorganic phosphorus?IP?and iron and aluminum oxidation state phosphorus?NaOH-P?were the main sources of phosphorus in sediments of Zhushan Bay and Meiliang Bay.From June to August,the content of NaOH-P increased gradually,and reached the maximum in August.In September and October,the content of NaOH-P decreased obviously,and the content of organic phosphorus?OP?increased significantly.There was a significant positive correlations between various forms of phosphorus in sediments,especially NaOH-P and total phosphorus?TP?,IP was stronger,and a significant positive correlation between phosphorus and TOM in sediments.The results of³¹P-NMR determination showed that the OP in sediments was mainly composed of phospholipid and DNA with strong activity from June to August,and stable monophosphates and monophosphates were the main factors in September and October.4.During the sampling period,the high resolution profile information of dissolved reactive phosphorus?DRP?and Fe²⁺in sediments was obtained by DGT.From June to October,the trends of DRP and Fe²⁺at sediment-water interface of Zhushan Bay and Meiliang Bay were similar.There was a peak concentration at the interface.Compared with other months,the peak concentrations of DRP and Fe²⁺in July and August were higher,the peak position was shallower,and the phosphorus concentration gradient at the sediment-water interface was higher.The release flux of DRP at the interface was positive from June to October.In July and August,the fluxes of phosphorus release were significantly higher than those in other months.There was a significant positive correlation between the release flux of DRP and Fe²⁺,indicated that the release of phosphorus in sediment-water interface was strongly influenced by Fe²⁺in July and August.5.From June to October,the values of phosphorus adsorption and desorption equilibrium?EPC₀?in sediments were higher than the contents of PO₄^3-in overlying water,indicated that sediments were releasing phosphorus during the sampling period.Maximum adsorption capacity(Q_max)was significantly negatively correlated with EPC₀,organic matter,TP,IP,and NaOH-P.Adsorption constant?K?was significantly negatively correlated with EPC₀,indicated that the increase of organic matter and phosphorus content in sediments would weaken the adsorption capacity of the sediments to phosphorus.The higher the value of EPC₀,the smaller the adsorption capacity of the sediments to phosphorus.In July and August,the contents of organic matter and phosphorus in the sediments of Zhushan Bay and Meiliang Bay were higher,and the value of EPC₀ were higher than those in other months,indicated that the adsorption capacity of phosphorus in sediments was relatively smaller in July and August,there was a large space for phosphorus release.