| The evolution of nitrogen content in experimental closed circuit ¿and filters was followed, each tank being fed with different quantities of soluble organic matter. According to the trophic conditions, two types of metabolism could be observed : - a loss of nitrogen (denitrification), reaching almost 90% of the nitrogen input in eutrophic conditions, and close to 35% in mesotrophic conditions. - a gain in nitrogen (fixation), a predominant metabolism in oligotrophic and eutrophic conditions. Nitrogen retention in the sediment increases slightly with the organic matter input, but no proportionality could be established. It seems that the sediment, by its bacterial metabolisms, regulates its own organic matter richness. |
