Distribution Characteristics Of Phosphorus Species Of A Deep Lake And Its Influencing Factors

Eutrophication is an important issue in water environment research of lakes.Nitrogen and phosphorus concentrations in lake water are the major influencing factors of eutrophication degree,with most lakes being delineated as phosphorus limitation.Research on phosphorus speciation distribution in shallow lakes like Lake Taihu are more than those in deep lakes in western China.Water quality deterioration are looming in plenty of phosphorus limitation deep lakes in western China,thus systematic investigations and research on cycle and transformation rule of different species of phosphorus are necessary.Research on temporal and spatial distribution and its influencing factors of major water environment factors and different species of phosphorus and its vertical distribution of Longjing Lake,Chongqing were conducted.The conclusions are as follows:(1)There were apparent seasonal variations in major water environment factors in pelagic and littoral zone.Temperature,dissolved oxygen and chlorophyll a in water column was homogeneous in vertical distribution in winter and stratified in autumn,spring and summer.(2)Phosphorus in Longjing Lake is in multiple forms.Total phosphorus(TP)in pelagic zone surface water was relatively high,with an annual concentration of 0.104 mg/L.Among which annual concentrations of dissolved phosphorus(DP),particulate phosphorus(PP),soluable reactive phosphorus(SRP)and dissolved organic phosphorus(DOP)were 0.054 mg/L,0.050 mg/L,0.039 mg/L and 0.015 mg/L,with proportions of 52%,48%,37.5% and 14.5% in TP,respectively.The ratio of SRP,DOP,DP and PP were almost the same among suface and medium water of pelagic zone and surface,medium and benthic water of littoral zone.Anuual concentration of TP in benthic water of pelagic zone was 0.265 mg/L,among which concentrations of DP,PP,SRP and DOP were 0.230 mg/L,0.035 mg/L,0.201 mg/L and 0.029 mg/L,with proportions of 87%,13%,75.7% and 11.3% in TP,respectively.(3)Annual variation rule of TP,DP and SRP of surface water in pelagic zone was high in winter and low in other time.Annual variation pattern of TP,DP and SRP in medium water was high in autumn and winter and low in spring and summer.Annual variation pattern of TP,DP and SRP in benthic water is high in autumn and winter and low in spring and summer and the maximun and minimum were in October and April,respectively.The impact of seasonal hypoxia in pelagic benthic water on annual variation rule of different phosphorus species was decisive.Annual variation pattern of TP,DP and SRP in surface,medium and benthic water is high in winter and low in other time.Concentration of DOP in surface,medium and benthic water in pelagic and littoral zone was 0~0.05 mg/L,relatively low and having little influence on phosphorus cycle in Longjing Lake.(4)TP,DP and SRP concentrations in pelagic zone were vertically homogeneous in winter and markedly stratified in other seasons.Little fluctuation were found in vertical concentrations of PP and DOP.Concentrations of different phosphorus species in littoral water coloumn in the whole year were homogeneous in general.concentration gradients only occur with particular parameters in particular seasons,like the decline of autumn TP concentration along depth.Vertical distribution of TP,DP and SRP concentrations in different seasons in littoral zone was characterised by high in winter and low in other seasons.Vertical variation of different phosphorus species in pelagic zone was mainly influenced by seasonal hypoxia in benthic water,whereas vertical variation of different phosphorus species in littoral zone was exerted multiple influence by benthic hypoxia and latteral exchange in water with the same depth in pelagic zone.