MEPS 191:33-41 (1999)  -  doi:10.3354/meps191033

ABSTRACT: Rates of actual nitrification through acetylene blockage of NH₄⁺ oxidation and potential nitrification were measured in 2 intertidal geomorphological structures, 'ridges and runnels', at Marennes-Oléron Bay, France. Nitrification rates were 6 times higher in runnels as compared to ridges and their O₂ gradients with depth were different. Calculated N mineralization rates averaged 1.66 mmol m^-2 d^-1 in runnels versus 0.29 mmol m^-2 d^-1 in ridges: Over 70% of this produced NH₄⁺ was nitrified and thus became potentially available for denitrification. In neither ridges nor runnels was there a significant correlation between potential nitrification and pH, E_h or pore water NH₄⁺ (p > 0.05), but the correlation between potential nitrification and pore water NO₃^- was significant in runnels (p <\ 0.05). The presence of nitrifying bacteria below the depth of O₂ penetration in sediment suggests that mixing processes have a role in controlling nitrification in this mudflat.

KEY WORDS: Atlantic · Intertidal mudflats · Nitrification · Ridges · Runnels