| Phosphorus(P)is one of the key limiting factors of productivity in coastal wetland,and organic phosphorus is an important component of phosphorus.The hydrolysis of organic phosphorus plays an important role in the process of eutrophication evolution and the conversion rate determines the nutrient status and productivity of the wetland.Therefore,the present study collected surface sediments and water samples(0 ~ 0.5m)in different seasons and at different locations at the Rong Cheng Swan Lake.The bioavailability and seasonal variation of organic phosphorus in lake water and sediments were studied via enzymatic hydrolysis.The correlation analysis was conducted to reveal the effects of organic phosphorus on water quality and eutrophication.Phosphatase activity and enzymekinetic characteristics were analyzed to reveal the controlling factors of organic phosphorus turnover.Finally,the fluxes of phosphorus between water sediment interface were calculated,and the contribution of organic phosphorus to the soluble inorganic phosphorus was discussed.The main findings and conclusions are shown as follows:(1)The water quality was III-IV and water has been a slight eutrophication in Swan Lake.Organic phosphorus was an important component of TP in Swan Lake.The content of DOP was 0.039~ 0.123 mg/L,accounting for 29% ~ 74% of total phosphorus.POP content was 0.011~0.073 mg/L,accounting for 11%~25 % of total phosphorus.The enzymatic hydrolysis of organic phosphorus showed that 24%~31%of DOP and 41%~82 % of POP were potential available phosphorus.The content of dissolved phosphorus varied with seasons: among which DTP and DOP are characterized by higher content of spring/summer than that of autumn/winter,whereas DIP followed distinct seasonal variation with higher conent in autumn/winter than that of spring/summer.The organic phosphorus was concentrated in center lake and river estuary area with heterogeneity.The correlation analysis suggested that DOP and enzyme hydrolysis phosphorus(EHP)such as Monoester-P and Diester-P could be used as an indicator of primary productivity and eutrophication.(2)The organic phosphorus content in the sediments of Swan Lake was 107.9~161.9 mg/kg,accounting for 25% ~ 40% of total phosphorus,and 37% ~ 50% of organic phosphorus was potential available.The sediment organic phosphorus did not varied greatly with seasons.The sediment EHP significantly changed in lake area.The monoester phosphorus(Monoester-P)and diester phosphorus(Diester-P)were concentrated in the river estuary and center lake,while phytate phosphorus(Phytic-P)was distributed mainly in center lake and sea estuary.Correlation analysis showed that sediment organic phosphorus,the important source of phosphorus in water,was closely related to water quality.In view of eutrophication,the release and hydrolysis of organic phosphorus need further investigation.(3)The activity of alkaline phosphatase,phosphodiesterase and phytase in Swan Lake,respectively,were 0.02~0.2 mg/(L?h),0.02~0.1mg /(L?h)and 0.2~0.3mg /(L?h).The activity of alkaline phosphatase and phosphodiesterase in the sediments of Swan Lake,respectively,was 6.1~11.7 mg /(kg?h)and 2.1~9.7 mg/(kg?h).The turnover time of Monoester-P,Diester-P and Phytic-P in the water of Swan lake,respectively,were 0.2~5.9 h?7.0~37.6 and 3.9~7.7 h.The turnover time of Monoester-P and Monoester-P in the sediments were0.1~0.2 h and 0.1~0.3 h,respectively.(4)The flux of organic phosphorus between sediment-water interface was1.8~3.2 mg /(m2?d)with average 2.4 mg /(m2?d).The annual flux of organic phosphorus was 21.7~99.2 t/a,which accounted for 52% of total phosphorus flux.The enzymatic hydrolysis rate of DOP was 0.3~1.3mg/(L?d)in surface water in Swan Lake.The amount of DIP per day is 13.4 ~115.4 times of water DIP,and the DOP cycle time ranged 0.008~0.08 d.In comparison,the sediment organic phosphorus hydrolysis rate was 5.2~11.3 mg/(kg?h)and represented 48% ~96% of sediment inorganic phosphorus,and the cycle time ranged 1.0~2.1d.The inorganic phosphorus flux between the sediment-water interface was calculated as 0.0017 ~0.006 mg/(L?d)and accounted for 9%~50% of sediment inorganic phosphorus.The diffusion time for inorganic phosphorus was 4.0~21.2 d.The flux of organicphosphorus between sediment-water interface ranged 0.0018~0.0064 mg/(L?d),and the diffusion time for DOP was19.5~98.4d.The daily flux of organic phosphorus between sediment-water interface accounted for 2%~10% of water DOP.The results show that the decomposition rate of organic phosphorus in lake water was very fast,and it can quickly supplement the dissolved inorganic phosphorus in water.Compared with the sediment water interface exchange,organic phosphorus becomes the main source of dissolved inorganic phosphorus in water.In conclusions,the content of potential available organic phosphorus in the water and sediments of Swan Lake is very high.For eutrophication remediation,organic phosphorus deserved further investigation.When external phosphorus load was reduced,the internal phosphorus cycling via organic phosphorus hydrolysis represented an important source of water phosphorus.However,the release of endogenous organic phosphorus is controlled by factors such as phosphatase,temperature,DIP and algae,etc.Therefore,in the process of eutrophication management,it is necessary to prevent and control the release of endogenous phosphorus from various angles. |
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