Nitrification in the intertidal zone: influence of effluent type and effect of tannin on nitrifiers

Nitrification by intertidal sediments was measured by using a tide simulator that approximated the cycle of seawater on tidal flats. Sediments were chosen from sites affected by industrial and municipal effluents and pastoral seepage and runoff. The ability of sediments from different sites to nitrify endogenous nitrogen varied markedly. All sites exhibited an initial lag before activity commenced. The duration of this lag and the rate of nitrate production were different at each site. The sediments were also capable of oxidizing NH3-N supplied to them in seawater. This "nitrification potential" was highest at sites receiving nitrogenous effluents (slaughterhouse and sewage), but was also substantial in sediments affected by bark extract effluent and pasture runoff. The lowest potential and the longest lag were exhibited by sediments in an apple cannery effluent area. Enrichment cultures of nitrifying microorganisms were obtained from all sites using NH4+ as a source of energy, but enrichments for nitrite oxidizers were unsuccessful. Concentrated pine bark tannins, similar in origin to those in effluents at the well-nitrifying chipmill site, were tested for toxicity to pure cultures of nitrifying bacteria. Two Nitrobacter strains and one Nitrosomonas strain were unaffected by tannins even at 5 mg/ml. A Nitrosolobus and a Nitrosospira strain were inhibited partially at 5 mg/ml and only slightly or not at all at 1 mg/ml.