Mass balance rates for nitrate, nitrite, ammonium and sulfate (nmol cm-2 h-1).

Statistical significance (p value included in the table) of differences in concentrations before and after the flow-through chamber were tested by Signed Rank test during the different incubations: increasing amount of sulfate and no added nitrate (Δ SO42—, Δ0 NO3-, n = 22), increasing amount of nitrate in presence of 2 mM sulfate (2 mM SO42-, Δ NO3-, n = 17) and 10 mM sulfate (10 mM SO42-, Δ NO3-, n = 24). Values are the mean of the difference ± SD of the experiments at variable sulfate or nitrate concentrations. Positive and negative values represent respectively net production and net consumption in the biofilm. Marked with an asterisk are rates with a p value below 0.05.