Éléments nutritifs (N et P), métaux lourds (Zn, Cu, Pb et Hg) et productivité végétale dans un marais intertidal d'eau douce, Québec (Québec)

The N and P content in the sediment of the intertidal freshwater marsh of Quebec City (St. Lawrence River) was analyzed in relation with the phytomass on the site. The heavy metals (Zn, Cu, Pb, and Hg) content in plants and sediment was also measured and the seasonal and comparative evolution of the concentrations was studied in relation with the biomass and productivity of vascular plants. The variations in NO2–NO3, NH4 and orthophosphate in tidal water between the flood and the ebb were studied. The mass balance of NH4 and orthophosphate in tidal water is positive toward the marsh, but the 5.5 kg/ha NH4 and 5.4 kg/ha PO4 that are trapped on the marsh are considered as low compared with the sediment contribution. Approximately 1323 mg N/kg dry weight and 41 mg P/kg dry weight are assimilated by plants from sediments during the growing season. Plants would actively assimilate Hg, whereas Pb and Zn would be passively absorbed; Cu is more actively assimilated in the roots during the maximum growth period. T...