Study On The Annual Varieties And The Influences Of Nitrogen, Phosphorus And Metal Of Sediments In Taihu Lake And Yuyuantan Lake

It is well known that China has many lakes. With the increasing of human activities, eutrophication status is more serious with frequent algae blooming, abundance alga species and broadest distribution. As the storage of nutritions, sediments are the main source of nitrogen and phosphors for algaes to grow and break out. The mechanisms of shallow lakes eutrophication were also complex. Along with the three-dimension model were put forward. Overlying water, sediment and biological dimension become the future emphasis of research subjects. Consequently study on the all kinds of transport and processes of nutrient matters should attach importance to the effects of biological dimension. This study is crucial to indicate eutrophication and blue algal bloom breaking out, and also show the contribution and mechanisms of sediments for eutrophication. This paper was supported by nation natural science fund"The effects from the release of lake sediments nutrition on the successions of algaes"(20507017).Objects of this investigation are two different eutrophic state adlittoral lakes—Taihu lake and Yuyuantan lake. The seasonal varieties and contents of nitrogen, phosphorys and metal of the two lakes are studied. Based on this study, we simulated the condition of eutrophication, selected different configurations of iron in order to study the different relations between irons and algaes. Furthermore biological factors (algaes) were added in the simulated experimental system to get the influence of the growth of algaes. Resrlts are as follows:(1)Investigation of water in Yuyuantan lake shows that this lake is in the eutrophic state. The lake enters into eutrophic state in June. Compared to September, all nutrition substances are much lower in October which shows the character of source in summer and collections in antumn. Compared with the overlying water, the contents of all nutrition substances changes very little in the clear water, However, it shows character of source in summer and collections in Antumn. The varietions of APA in clear water and lake water from different sample sites are almost the same.The concentrations of APA raise constantly from March on.With the bloom of eutrophication,the concentrations of APA fall to a certain level. The proportions'order of the four different BAPs in TP at the four sampling sites are indentical: AAP>Olsen-P>RDP>WSP.(2)The variations of the TN concentrations in different sample sites are not very significant.for the first sampling site, the most polluted one, its max concentration of NH4-N occurs in June;The max concentrations of NH4-N of the other sample sites occur in August.The concentrations of NO3-N are all not very high in one year. For the west lake, whose pollution is more serious, its concentration of IP takes a large part of TP in the sediments,while the concentration of OP takes a large part in the east lake. The different phosphors forms all have good positive correlations with the total phosphor.All nutrition substances contents in the west lake are higher than the east lake,which is positive correlate with the pollute conditions.(3) The concentrations of heavy metals, such as As, Cd, Cu, Pb, Zn in different sediments collected from the Meiliang Bay, Xukou Bay and Gonghu Lake in the northwest of Taihu Lake in different seasons, have some relativities with the clearance water temperatures, pH, Eh and the total nitrogen ,total phosphorus ,organic matters, sediment granule diameters etc. The ranking of concentrations of heavy metals in different sediments collected from the Taihu Lake is Meiliang Bay> Gonghu Lake> Xukou Bay .The result shows that: A varieties of heavy metals'concentrations in one year have a certain relationship with the contaminative conditions; For the Meiliang Bay, which is the most eutrophicated , its max concentrations occurr in Septermber; the max concentrations of heavy metals in the other two lakes occurr in June; The concentrations of heavy metals are influenced by the temperatures, pH and Eh etc; the concentrations of heavy metals have some positive correlations with the temperatures, pH and Eh ; The concentrations of heavy metals are also influenced by the total nitrogen ,total phosphorus ,organic matters and sediment granule diameter etc; the concentrations are positive correlated with the organic matters and sediment granule diameter, the concentrations of heavy metals are negative correlated with the total nitrogen ,total phosphorus.(4)The maximum biomass in single and competitive cultivation between different alage species of Green Algae(Scenedesmus quadricauda),Blue-green Algae(Microcystis aeruginosa)and Diatom(Cyclotella)are all Scenedesmus quadricauda > Microcystis aeruginosa > Cyclotella.In single cultivations, Scenedesmus quadricauda is the dominant species,whose biomass is always in the leading role ,especially in the medium and high Fe2+ and Fe3+ concentrations.The most optimum concentration of Cyclotella and Microcystis aeruginosa are the same.But Microcystis aeruginosa are more adapted to higher concentration of Fe2+ and Fe3+.In the competitive cultivation,the biomass of Cyclotella and Microcystis aeruginosa are not very big.In the single cultivations,the maximum biomass of the three algaes don't raise with the increase of Fe2+ and Fe3+. The maximum biomass of Cyclotella occurs in Fe2+200mg/L and Fe3+2000 mg/L.The maximum biomass of Scenedesmus quadricauda occurs in Fe2+200mg/L and Fe3+2000 mg/L. The maximum biomass of Microcystis aeruginosa occurs in Fe2+500mg/L and Fe3+5000 mg/L.It shows that the middle and lower concentrations of Fe2+(200~500 mg/L)and the higher concentrations of Fe3+(2000~5000 mg/L)are the most suitable concentrations for the three algaes.In the competitive cultivation, the growth of Cyclotella and Microcystis aeruginosa are not very well.The growth of Scenedesmus quadricauda has been restrained to some extent,which hasn't reach the biomass in single cultivation. Scenedesmus quadricauda shows obvious advantage in the competitive cultivation.(5)Analysises in the biomass,logarithm grow period and increase speed find that when single cultivated , Scenedesmus quadricaudan has the absolute advantage,especially in the middle concentrations of Fe2+ and higher Fe3+.The most suitable concentrations of Cyclotella is the same with Scenedesmus quadricaudan.But Microcystis aeruginosa are more suitable with higher Fe2+ and Fe3+.So in single cultivations,the Scenedesmus quadricaudan are more adapt to the high nutritions than Microcystis aeruginosa and Cyclotella.