MEPS 294:35-49 (2005)  -  doi:10.3354/meps294035

ABSTRACT: A recolonisation experiment was performed in vitro on highly reduced laminated Baltic Sea sediments initially devoid of larger benthic fauna. The survival capacity of 3 common benthic species Monoporeia affinis, Macoma balthica and Marenzelleria viridis was investigated along with overall effects of bioturbation and bioirrigation on benthic reaction and transport processes. Benthic fluxes of oxygen and nutrients, sediment denitrification and nutrients in the porewater were measured. Survival of M. affinis increased with time and sediment reworking, while no such feedback was observed for M. balthica and M. viridis. Macrofaunal irrigation and bioturbating activities significantly enhanced solute fluxes in the manipulated cores compared to the control. Mass balance calculations indicated that net N-mineralisation in the manipulated cores was stimulated by 1 to 2 orders of magnitude compared to the control. Despite relatively high nitrate fluxes from the overlying water to the sediment (~1 mmol m^–2 d^–1), measured rates of total denitrification were in general low (20 to 45 µmol N₂ m^–2 d^–1) in all cores. Denitrification, using nitrate supplied from the overlying water (D_w), was similar to coupled nitrification/denitrification (D_n), although D_w was significantly higher than D_n in the M. affinis cores. In conjunction with high nitrate fluxes into the sediment and high ammonium fluxes to the overlying water, the generally low denitrification rates indicated dissimilatory nitrate reduction to ammonium (DNRA) as the main pathway for nitrate removal. Thus, the main source of bottom water ammonium was overlying water nitrate, rather than ammonium produced in surface sediments during mineralisation of organic N.

KEY WORDS: Recolonisation · Bioturbation · Macrofauna · Baltic Sea · Reduced sediments· Benthic fluxes · Denitrification · Mineralisation