Interaction of benthic microalgae and macrofauna in the control of benthic metabolism, nutrient fluxes and denitrification in a shallow sub-tropical coastal embayment (western Moreton Bay, Australia).

摘要

Benthic biogeochemistry and macrofauna were investigated six times over 1 year in a shallow sub-tropical embayment. Benthic fluxes of oxygen (annual mean -918 micro mol O₂ m-2 h-1), ammonium (NH₄+), nitrate (NO₃-), dissolved organic nitrogen, dinitrogen gas (N₂), and dissolved inorganic phosphorus were positively related to OM supply (N mineralisation) and inversely related to benthic light (N assimilation). Ammonium (NH₄+), NO₃- and N₂ fluxes (annual means +14.6, +15.9 and 44.6 micro mol N m-2 h-1) accounted for 14, 16 and 53% of the annual benthic N remineralisation respectively. Denitrification was dominated by coupled nitrification-denitrification throughout the study. Potential assimilation of nitrogen by benthic microalgae (BMA) accounted for between 1 and 30% of remineralised N, and was greatest during winter when bottom light was higher. Macrofauna biomass tended to be highest at intermediate benthic respiration rates (-1,000 micro mol O₂ m-2 h-1), and appeared to become limited as respiration increased above this point. While bioturbation did not significantly affect net fluxes, macrofauna biomass was correlated with increased light rates of NH₄+ flux which may have masked reductions in NH₄+ flux associated with BMA assimilation during the light. Peaks in net N₂ fluxes at intermediate respiration rates are suggested to be associated with the stimulation of potential denitrification sites due to bioturbation by burrowing macrofauna. NO₃- fluxes suggest that nitrification was not significantly limited within respiration range measured during this study, however comparisons with other parts of Moreton Bay suggest that limitation of coupled nitrification-denitrification may occur in sub-tropical systems at respiration rates exceeding -1,500 micro mol O₂ m-2 h-1.