Effects of metals on nitrogen fixation and denitrification in slurries of anoxic salt-marsh sediment

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Abstract
The effect of metals on N fixation, as measured by acetylene reduction, and on denitrification, as determined by N2O accumulation in the presence of acetylene (acetylene blockage), was examined in short-term experiments with saltmarsh sediments. At 1000 ppm (wt metal:wt dry sediment), HgCl2, PbCl2, CdCl2, ZnSO4, CuCl2, K2Cr2O7, K2CrO4 and Na2MoO4 decreased acetylene reduction throughout the experiments 30%. FeCl3 decreased it to a lesser extect, while NiCl2 greatly stimulated nitrogenase activity. Initial rate of N2O production was inhibited by HgCl2, PbCl2, NiCl2, K2Cr2O7, K2CrO4, ZnSO4, CuCl2, FeCl3 and CdCl2, but maximum production was stimulated substantially by PbCl2, K2Cr2O7 and K2CrO4, and somewhat by Na2MoO4, ZnSO4 and CuCl2. NiCl2 depressed initial and maximum N2O production. Lower levels of Ni and Hg (10 and 100 ppm) caused effects that were intermedaite between 1000 ppm and controls. Metal pollution considerably altered N dynamics in marine sediments, at least in the short term; and could have had repercussions on water-column productivity.