Study On The Nutritional Characteristics Of Different Lake Sediments And The Responsive Growth Of Submersed Macrophyte Potamogeton Crispus L. In The Sediments

The recovery and growth of aquatic submersed macrophytes is an important and effective measure for phytoremediation of eutrophic lake ecosystem.But so far it was difficult for aquatic submersed macrophytes to grow successfully in eutrophic lake.In this process,nutritional levels in the environment had great influence on the submersed macrophytes growth.Through the transplanted experiments of submersed macrophyte Potamogeton crispus L.in Taihu Lake,Tangxunhu Lake and Yuehu Lake sediment in the laboratory,from the view of mineral nutrients,we studied the growth of P. crispus in different lake sediment,by comparing the variance of P.crispus growth,nutrients content and seasonal change in different lake sediment.And after P.crispus grew successfully,we kept on the study of the influence of P.crispus growth on water pH,the formation of root plaques around root,the effects of P.crispus growth on nutritional levels in sediment and overlying water by comparing the variance of nutrients content in sediment and overlying water between treatments of P.crispus growth with controls of no P.crispus growth.Through the study,we got the primary results as followed:1) By the study of P.crispus growth in different types of substrate and overlying water,we found that as surface sediment of Taihu Lake was substrate,P.crispus shoots growth was advanced while propagules generation was inhibited.As quartz sand was substrate,P.crispus shoots growth was inhibited while propagules generation was advanced.The concentration of Ca and Mg in P.crispus was mainly influenced by Ca and Mg concentration in overlying water.The concentration of Fe and Mn in P.crispus was mainly influenced by Fe and Mn levels in sediment.The concentration of Cu and Zn in P.crispus was influenced by overlying water and sediment at the same time.2) By comparing P.crispus growth in Taihu Lake,Yuehu Lake and Tangxunhu Lake sediment, we found that P.crispus could grew well in all sediments,but there was difference for P.crispus growth in different sediment.P.crispus grew better in Taihu Lake sediment when compared with that in Yuehu lake sediment;P.crispus grew worst in Tangxunhu Lake sediment.There were significant differences for shoots biomass,roots biomass,propagules biomass and germination rates in different sediments.3) By the study of P.crispus growth in sediment of different sites in Taihu Lake and Yuehu Lake, it was found that flourish shoots growth would be helpful for the generation of propagules of P. crispus,although there was no corresponding relationship between germination rates of propagules with P.crispus growth.The significant relationship existed between sediment nutritional levels and P. crispus growth.In the initial stage of P.crispus growth,the enrichment of nutrients in sediment inhibited shoots growth.With the time gone,influence of sediment nutritional levels became weak gradually.After the period of flourish growth,there was significant positive relationship between Mn content in sediment with biomass of P.crispus.The enrichment of P,Cu and Zn in sediment would inhibit the propagules generation.4) The different nutrients in P.crispus represented obvious and different seasonal changes.The same nutrient had similar seasonal changes in tissue of P.crispus growing in different sediment.The nutritional levels in sediment had influence on the nutrients concentration in P.crispus,while had no influence on the trend of seasonal changes of nutrients in P.crispus.There were differences for the distribution of different nutrient elements in plant tissue.In general,Fe,Mn and Zn conc.were highest in roots,then in shoots,lowest in propagules.Mg conc.was highest in shoots,then in roots,lowest in propagules.Ca and P conc.were lowest in propagules compared with shoots and roots.Cu conc.in propagules was in-between of shoots and roots.Nutrients conc.in different parts of P.crispus was influenced by the nutritional levels in sediment.Compared with shoots and roots,the influence of sediment was less in nutrients concentration in propagules.5) With P.crispus growth,pH of overlying water was significantly elevated.The illumination had great influence on the changes of pH in overlying water,which caused overlying water pH represented diurnal changes.Beside of P.crispus growth,substrate had some influence on the pH changes of overlying water by direct and indirect effects.6) The formation of root plaque around P.crispus root caused elements concentrated in the root surface,further influenced the elements uptook by roots and elements distribution in root section.Root plaque formation around the roots of P.crispus had influence on Fe,Mn,Si and P conc.and distribution in root surface and section,had some effects on Al and Ca,while had no effects on Mg, Cu and Zn in roots.For the different characteristics of root plaque formation around roots in Tangxunhu Lake sediment and Yuehu Lake sediment,the influence of root plaque on nutrient elements uptook by roots was different between P.crispus grew in Tangxunhu Lake sediment with Yuehu Lake sediment.7) Compared with the control,P.crispus growth had influence on the water-extracted nutrients conc.in sediment and nutrients conc.in pore water,overlying water.The effect of P.crispus growth on water-extracted nutrients conc.in sediment,nutrients conc.in pore water and overlying water was complicated for different time,different nutrients and different sediment.Generally,after the period of returning-green and flourish growth,the influence of P.crispus growth became more obvious.P. crispus growth had less influence on the nutrient conc.changes in overlying water,by comparing with the influence on changes in water-extracted nutrient conc.and nutrient conc.in pore water.