Effects of Cu,Pb and Zn on two Potamogeton species grown under field conditions

Two common macrophyte species, Potamogeton perfoliatus L. and Potamogeton pectinatus L. were grown for 12 weeks at shallow depths in sediments contaminated with 1250 or 2500 g Pb or Cu and/or Zn (gDW sediment)^-1. Control experiments were run at background levels of 4, 13, and 38 g Pb, Cu and Zn (gDW sediment)^-1, respectively. Effects of heavy metals on biomass production and metal uptake and distribution in plants are presented in relation to total amount and plant-available fraction of metals in the sediment.All three studied metals gave reduced biomass production, and the toxicity of the metals decreased in the order Zn>Cu>Pb. The root/shoot biomass ratio increased for P. pectinatus, but decreased for P. perfoliatus with metal treatment. The content of any single metal was higher in shoots than in roots of plants grown on sediments not contaminated with that specific metal, but addition of that metal increased the proportion in roots. The uptake by plants of any of the heavy metals increased with increased metal addition. The magnitude of the plant-available fraction of metals of untreated sediment was Zn>Cu>Pb, and increased in contaminated sediments. Addition of Cu decreased both the plant-available fraction and the total concentration of Zn in the sediment, while increased the uptake of Zn by the plants. The opposite was found for Cu when Zn was added. P. pectinatus accumulated about twice as much Cu as P. perfoliatus. On the other hand, the concentration of Pb was higher in P. perfoliatus than in P. pectinatus, and was negligible in P. pectinatus when cultivated in untreated sediments.