As the biggest freshwater wetland in North China, Baiyangdian Lake is facing the problems of eutrophication and sediment contamination by heavy metals especially for Pb and Cd. Submerged macrophyte has shown tremendous potential to remove pollutants from water. In addition, since submerged plants are exposed to both overlying water and sediment, the translocation of metals in plants can affect their biogeochemical cycle in water system. However, there is little information available on the influences of N and P, which are the key limiting nutrients in eutrophication, on heavy metal translocation in submerged plants. As a result, effects of N and P nutrient on Pb translocation and accumulation in submerged macrophyte Potamogeton crispus L. were investigated. Root of P. crispus were exposed to 50 mg/kg Pb contaminated sediment with different N (NH₄NO₃) and P (KH₂PO₄) concentrations (N 0.5 g/kg, N 5 g/kg, N0.5+P0.5 g/kg, N 5+P5 g/kg) to explore the influence of macronutrient on Pb translocation and accumulation of Pb in sediment- submerged plant-water system using the sequestered chamber.

Results showed that Pb accumulation in plants decreased in the order of leaves>stems>roots. N addition in sediment showed no significant influence on Pb accumulation in roots, while promoted upward translocation of Pb, with translocation factor (TF) of N 0.5 and N 5 treatment increased by 36.76% and 17.48%, respectively, compared with that of control treatment (CK, without N and P). Therefore, bioaccumulation of Pb in shoot was enhanced after N addition in sediment. Bioaccumulation factor (BCF) of Pb in shoot of P. Crispus of N 0.5 and N 5 treatment was 36.76% and 17.48% higher than that of CK, respectively. Furthermore, after P addition in sediment, Pb accumulation in plants were significantly inhibited compared with single N treatment probably due to the immobilization of Pb by P in sediment. Pb concentrations in plant roots of N0.5+P0.5 and N5+P5 treatment was reduced by 82% and 85% compared with that of N0.5 and N 5 treatment, respectively. However, P in sediment inhibited translocation of Pb from root to shoot, TF of N0.5+P0.5 and N5+P5 treatment was reduced by 12% and 38% compared with that of N0.5 and N 5 treatment, respectively. The TF was >1 in all conditions, indicating that P. crispus promotes the translocation of Pb to shoots, while it was more obvious after adding P in sediment.On the basis of this experiment, the translocation and accumulation of Pb by P. crispus is affected by nitrogen and phosphate, and therefore, it can be a good candidate for the phytofiltration of this contaminant in different trophic level sediment.