Figure 2. Summary of the assumed interactions to explain the observed differences in N₂O production rates.

The assumed interactions which affect denitrification are indicated with dashed arrows. Bacteria mediated relevant reduction reactions of the nitrogen pathway and sulfur pathway are enclosed by grey boxes indicated with respectively ‘N fluxes’ and ‘S fluxes’. Copepods feed on both diatoms and bacteria, and produce excretion producs (excretions). Bacteria feed on the excretion produces and are also responsible for the reduction of SO₄ ^2- to H₂S and of NO₃ ^- to NH₄ ⁺ (DNRA) and N₂O+N₂ (denitrification) in the microcosm. The produced NH₄ ⁺ is assimilated by both bacteria and diatoms. Copepods affect the N₂O production rate by producing excretion products which provide an extra carbon source, of which mainly the DNRA bacteria can take advantage (1) and also enhances SO₄ ^2- reduction (2a), which results in more H₂S. The increased H₂S inhibits denitrification (2b). Diatoms have no direct effect on the N₂O production rate, but do have an indirect effect by enhancing the survival of the copepods (3) and influencing the quantity and composition of the copepods' excretion products (4).