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

Nitrification rates related to sedimentary structures in an Atlantic intertidal mudflat, Marennes-Oléron Bay, France

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, Eh 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

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