MEPS 331:195-205 (2007)  -  doi:10.3354/meps331195

ABSTRACT: A laboratory experiment was carried out to investigate the overall effects from the diurnal bioturbating activities of Monoporeia affinis on benthic solute fluxes. Investigations were performed on Baltic Sea sediments during a 12:12 h light:dark cycle, where light conditions (1 µmol photons m^–2 s^–1) corresponded to those at a simulated water depth of 25 m in July. Oxygen consumption, nutrient [NO₂^– + NO₃^–, NH₄⁺, Si(OH)₄ and HPO₄^2–] fluxes and denitrification rates were analysed after organic material enrichment (5 g C m^–2) of the sediment. Significant effects from the diurnal activity of M. affinis could be observed, as enhanced solute fluxes of O₂, NO₂^– + NO₃^–, NH₄⁺ and HPO₄^2– were found during day (light) compared to night (dark) treatments. The diurnal activity of M. affinis showed no effect on denitrification rates. Irrigation of M. affinis, however, stimulated denitrification of the nitrate supplied from the overlying water (Dw) by about 50% compared to the control (no macrofauna). No effect on coupled nitrification/denitrification (Dn) was found. Diurnal activity of meiofauna seemed to have effects on solute fluxes as control cores (no macrofauna) also showed enhanced fluxes during the day compared to at night. In addition, effects from the endogenous diurnal activity of M. affinis were observed in cores kept in total darkness. This study highlights the importance of diurnal activity patterns of benthic fauna during studies of nutrient dynamics and sediment mineralisation processes.

KEY WORDS: Monoporeia affinis · Diurnal activity · Nutrient fluxes · Oxygen consumption · Denitrification · Baltic Sea