Influence of sediment and pore-water composition on nitrite accumulation in a nitrate-perfused freshwater sediment

Anaerobic nitrate consumption was accompanied by the accumulation of nitrite in the range of 3–52 μmol l−1 in laboratory sediment cores continuously perfused with nitrate from below. Highest interstitial nitrite concentrations were observed in organically poor sediment cores with a low extractable protein content. Supplemented with an additional source of fixed nitrogen (ammonium), the nitrate-perfused sediments exhibited considerably lower nitrite concentrations than the respective control treatments. The simultaneous addition of ammonium and chloramphenicol, however, resulted in high nitrite concentrations. This suggests that in the absence of chloramphenicol an ammonium-fuelled bacterial protein de novo synthesis prevented the accumulation of nitrite in the course of anaerobic nitrate consumption. Additional DOC (glucose, methanol) generally increased the anaerobic nitrate consumption rate and the interstitial nitrite concentrations. The different scales of these increases were probably related to the degradability of the respective DOC compound and to the taxonomic composition of the microbial community evolving under different feeding regimes.