The Effect Of Organic Matter And Submerged Macrophyte On Nitrogen & Phosphorus Mineralization And Pools In The Lake Sediment

Eutrophication is the most important problem concerning water environment. When the external nutrient loadings are controlled,sediment is becoming a major source of nitrogen(N) and phosphorus(P) releasing to overlying water.The inorganic N and P originated from organic matter(OM) mineralization in lake sediments are higher than those in soils.In our study,about 9%-39%of TN, 5.7%-26%of TP was mineralized in the lake sediments,and the heavily polluted sediment has higher mineralization rates and higher amounts of mineral-N and mineral-P than those of the slightly polluted sediment.Besides,intrinsic OM quality is an important factor which effects mineralization:after the removal of light fraction OM(LFOM) and dissolved OM(DOM),the net mineral-N and mineral-P as well as the N and P mineralization rates were decreased.Not only can LFOM be a potential source of mineralization,but also its removal demolished the binding matter and dispersed the sediment and thus resulted in therelease of inorganic N and P.What is more,DOM can affect the microbial biomass N and the activity ofurease and act as a potential source of mineralization.After comparing the net mineral-N of waterlogged incubation plus intermittent leaching with that of continuously waterlogged incubation,the results indicated that the maximum amount of net mineral-N of intermittent leaching was lower than that of continuously incubation.The net mineral-N of continuously incubation increased sharply at first and then the extent decreased;after reaching the peak values,the amounts decreased to the lowest and stayed minimum until the end of the incubation, while that of intermittent leaching kept increasing during the whole period.Because of the submerged macrophyte,Myriophyllum spicatum L.,the concentrations of the NH₄⁺-N,soluble reactive phosphorus(SRP) and total dissolved phosphorus(TDP) in the overlying water and the porewater were all decreased.The NH₄⁺-N and SRP concentrations of the porewater of rhizosphere sediment were lower than those of non-rhizosphere sediment.However,there is no evident differences of NO₃^--N and TDP concentrations between rhizosphere and non-rhizosphere sediment.