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. ) 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.

International audienceParticle and solute transport by faunal activities may significantly influence rates and pathways of organic matter mineralization during early diagenesis in surface sediments. One of the most frequently utilized techniques to quantify benthic biological reworking activities involves the calculation of a biodiffusion coefficient (Db) estimated from model predictions of 1-D tracer distribution patterns. This technique is labor-intensive and time-demanding. Furthermore, it is normally used for measurements over several days and averages overall transport mechanisms from 3-D to 1-D on a cm scale. In the frame of this work, we developed a new technique based on the nondestructive screening of fluorescent particles (luminophores) using optical discrimination and CCD camera detection of fluorescence (2-D). At a site characterized by a dense population of the brittle star Amphiura filiformis and a high biodiffusion coefficient (obtained from 1-D distributions; Db=35.5±3.7 cm−2 year−1; n=3), the optical reworking coefficient (ORC), estimated from the 2-D luminophore distribution patterns, was calculated (ORC=27.4±9.1 View the MathML source cm−2 h−1; n=24). A nondestructive 2-D approach to quantify particle reworking may provide a powerful and complementary tool to further understand particle transport by the benthic fauna in surface sediments. The optical technique for 2-D detection of luminophores is relatively fast and easy to perform, with the ability to detect small scale (mm) particle movements on a time resolution of minutes or less

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