PARENT SESSION
WA5a Bioavailability of Organic Chemicals: Concepts, tools and consequences
9:00 AM to 11:00 AM, Wednesday, 09 May 2001
Session Chair: J.J. Ortega
Room 5

(323) Importance of biogenic structures and sediment organic matter quality for the microbial degradation of pyrene.

Granberg, Maria ¹, Hansen, Rikke², Selck, Henriette², ^{1 2}

ABSTRACT- Aquatic sediments harbour a complex system of burrows, tubes and other biogenic structures. These structures differ significantly in their biogeochemistry compared to the surrounding sediment, with short diffusion distances between oxic and anoxic sediment-layers and solutes constantly moving due to macrofaunal ventilation. Tube walls are lined with mucus, altogether creating favourable conditions for bacteria. Biogenic structures has long been considered important for microbial mineralization of organic matter (OM) whereas knowledge is sparse on their importance for the degradation of organic pollutants. The study aims to investigate the importance of biogenic structures as active zones for microbial degradation of pyrene as a function of macrofaunal species and organic matter quality. The experiment consisted of a preexposure- and an incubation phase. During preexposure, brittle stars (Amphiura filiformis) and polychaetes (Nereis diversicolor) where added to separate aquaria containing organically enriched, pyrene contaminated sediment. Enrichment consisted of microalgae (nutritious OM) or lignin (poor OM). After 35 d the preexposure was terminated and samples from sediment surface, burrow walls and bulk sediment where recovered for the incubation phase. Samples where transferred to CO₂-traps spiked with ¹⁴C-pyrene. The traps where continously checked for ¹⁴CO₂ production during the 5 month incubation-period. The ¹⁴CO₂ production, i.e. microbial pyrene degradation potential (MPDP), was one order of magnitude higher in sediments preexposed to pyrene. There was a significant difference in MPDP between sediment compartments exposed to microalgae, and no difference in MPDP in those exposed to lignin. The MPDP in the microalgae treatment was highest in the surface layer, slightly lower in burrow sediment and lowest in bulk sediment. The MPDP pattern did not differ between species, however, MPDP was slightly lower for A.filiformis burrow sediment. Results stress the importance of biogenic structures and trophic state for the degradation of pyrene in aquatic sediments.

Key words: sediment burrows, pyrene, microbial degradation, organic matter quality