Denitrication and N₂O production in Canadian Lakes: effects of nutrient ratios acting through primary producer selection

Anthropogenic nutrient loading to aquatic systems may increase atmospheric release of nitrous oxide (N₂O) greenhouse gas by enhancing denitrification and/or nitrification. High Si:N loading may favour diatom abundance, whereas low N:P loading may favour cyanobacteria dominance. Systems with diatom or green algal dominance may have greater export of organic matter to sediments, whereas systems dominated by cyanobacteria may have organic matter recycled within the water column due to differences in cell density and sinking. With increased export of organic matter to sediments, denitrification and N₂O production may be stimulated. In laboratory bench-scale microcosms, nitrous oxide production was affected by Si:N loading ratios as predicted, although N:P loading did not affect N₂O production in the manner predicted. However, the predicted effects of nutrient loading ratio on microphyte community composition were not supported by microscopy. Field mesocosm experiments indicated no significant relationship between N₂O production and nutrient loading ratios.