52 Biogeuchemical Processes and InteractIon,
103
Decomposition of organic matter
Organic matter in marine sediments is mainly degraded via the activity of microorganisms (Fenchel & Blackburn 1979). Bacteria prefer fresh, easily degradable
and high-quality material with high contents of fatty acids and proteins (Grenz et
al. 1990). Thus they compete with other heterotrophic consumers for food. On the
other hand, bacteria produce high-quality food in liquid (acids) and solid form,
which can be used as food by meiofauna and protozoa (Bouvy & Sayer 1989).
Both groups can further improve the quality of food for detritus-feeding organisms
(Meyer-Reil & Faubel 1980). On a seasonal scale, an enhanced supply of fresh
organic matter of high quality exists especially during phytoplankton blooms.
When fresh organic matter is not available (e.g. during winter), some bacteria are
able to use refractory organic matter (lignin, humic acids and mucopolysaccharides) and decompose high-molecular substances into smaller components, which
in turn can be used by other organisms (Alongi & Hanson 1985). The lowmolecular products and soluble inorganic compounds of C, Nand P can also be
released from the benthic system into the overlying water (Billen 1978; Klump &
Martens 1981; Blackburn 1988; Hansen & Blackburn 1991). Apart from the mobilization of nutrients during the decomposition of organic matter, a release of Mn
and Fe by reduction of Mn/Fe-oxi Ihydroxides occurs (Sorensen & Jorgensen
1987; Canfield et al. 1993) as well as of trace elements. Released Fe is precipitated
relatively fast in the form of Fe-sulphide complexes, or reoxidised. Main factors
intluencing mineralization processes in intertidal sediments are fauna, bioturbation, irrigation, tidal pumping, wave pumping, diffusion and temperature (Sorensen
et al. 1979, Malcolm & Sivyer 1997).
Physiological groups of hacteria and substrate utilization
In ecophysiological investigations, bacteria are divided into physiological groups
and taxonomic criteria are only of minor importance. Due to the different environmental conditions, distinct bacterial populations occurred in the sandflat and in
the mussel bed sediments. Dividing bacteria into physiological groups, more copiotrophic organisms (adapted to high nutrient contents) and fermenting bacteria
were found in the mussel bed sediments. whereas more oligotrophic bacteria occurred at SP6 (sandtlat) (Leu unpubl. data). This showed that the bacterial populations were adapted to the environmental conditions at the tidal flat sites: to anoxic
conditions and a sufficient supply of degradable substrates in the biodeposits and to
oxic conditions and a lower (limited) supply of organic substrates in the sandtlat.
Experiments on the utilization of different microbial substrates (BIOLOGTM;
Zak et al. 1994), in which several carbon sources were offered to the microflora,
showed that the bacteria population in the mussel bed was able to transfer over
50 % of the offered substrates relatively quickly (within 12 h) (Albers unpubl.
data). This fast reaction indicated an adaptation of the bacteria to a high nutrient
supply. In contrast, the bacteria in the sandtlat could not use the offered substrates
until a time lag of 36 h had passed. However, after one day of incubation, the bacteria in the sandflat had developed the ability for the use of 90 % of all offered Csources, while the bacterial tlora in the mussel bed could use only approximately
103
Decomposition of organic matter
Organic matter in marine sediments is mainly degraded via the activity of microorganisms (Fenchel & Blackburn 1979). Bacteria prefer fresh, easily degradable
and high-quality material with high contents of fatty acids and proteins (Grenz et
al. 1990). Thus they compete with other heterotrophic consumers for food. On the
other hand, bacteria produce high-quality food in liquid (acids) and solid form,
which can be used as food by meiofauna and protozoa (Bouvy & Sayer 1989).
Both groups can further improve the quality of food for detritus-feeding organisms
(Meyer-Reil & Faubel 1980). On a seasonal scale, an enhanced supply of fresh
organic matter of high quality exists especially during phytoplankton blooms.
When fresh organic matter is not available (e.g. during winter), some bacteria are
able to use refractory organic matter (lignin, humic acids and mucopolysaccharides) and decompose high-molecular substances into smaller components, which
in turn can be used by other organisms (Alongi & Hanson 1985). The lowmolecular products and soluble inorganic compounds of C, Nand P can also be
released from the benthic system into the overlying water (Billen 1978; Klump &
Martens 1981; Blackburn 1988; Hansen & Blackburn 1991). Apart from the mobilization of nutrients during the decomposition of organic matter, a release of Mn
and Fe by reduction of Mn/Fe-oxi Ihydroxides occurs (Sorensen & Jorgensen
1987; Canfield et al. 1993) as well as of trace elements. Released Fe is precipitated
relatively fast in the form of Fe-sulphide complexes, or reoxidised. Main factors
intluencing mineralization processes in intertidal sediments are fauna, bioturbation, irrigation, tidal pumping, wave pumping, diffusion and temperature (Sorensen
et al. 1979, Malcolm & Sivyer 1997).
Physiological groups of hacteria and substrate utilization
In ecophysiological investigations, bacteria are divided into physiological groups
and taxonomic criteria are only of minor importance. Due to the different environmental conditions, distinct bacterial populations occurred in the sandflat and in
the mussel bed sediments. Dividing bacteria into physiological groups, more copiotrophic organisms (adapted to high nutrient contents) and fermenting bacteria
were found in the mussel bed sediments. whereas more oligotrophic bacteria occurred at SP6 (sandtlat) (Leu unpubl. data). This showed that the bacterial populations were adapted to the environmental conditions at the tidal flat sites: to anoxic
conditions and a sufficient supply of degradable substrates in the biodeposits and to
oxic conditions and a lower (limited) supply of organic substrates in the sandtlat.
Experiments on the utilization of different microbial substrates (BIOLOGTM;
Zak et al. 1994), in which several carbon sources were offered to the microflora,
showed that the bacteria population in the mussel bed was able to transfer over
50 % of the offered substrates relatively quickly (within 12 h) (Albers unpubl.
data). This fast reaction indicated an adaptation of the bacteria to a high nutrient
supply. In contrast, the bacteria in the sandtlat could not use the offered substrates
until a time lag of 36 h had passed. However, after one day of incubation, the bacteria in the sandflat had developed the ability for the use of 90 % of all offered Csources, while the bacterial tlora in the mussel bed could use only approximately