110
'; Spallal and Temporal Di,tnbutlOn Pattern,
plication of a two-component mixture model would lead to a marine proportion of
approx. 80 % in the surface sediment, which decreased to a proportion of approx.
20-25 % at 25 cm depth. This would indicate a preference for degradation of marine organic carbon.
A further characterization of the origin of marine organic matter (phytoplankton, macroalgae and other marine organisms) with organo-geochemical methods is
possible. For example, steroles are suitable to differentiate between the input of
macroalgae and diatoms into the sediment (Volkman 1986). Sterols are components of the cell membrane in all organisms except bacteria. Their different molecular structures permit a specific allocation to the source organisms, a modification of the structure indicates diagenetic processes. The comparison of the
concentrations of a steroid biomarker typical for diatoms (brassicasterol), with
those characteristic for macroalgae (fucosterol), indicated how these sources contributed to the composition of organic matter in the sediment over the year. The
results showed that an input of phytoplankton biomass into the sediment took place
in spring, while in autumn a macroalgal occurrence could be distinguished from a
following phytoplankton bloom (Brocks unpubl. data).
Effect of mussels on the quality of organic matter
The effect of blue mussels on organic matter could only be revealed when the
quality of this material was considered. The quality was assessed in samples taken
along the transect on the Swinnplate which were analysed for the proportion of
amino acids on the POc. In an additional mesocosm experiment, the pigment
composition was determined also (Behrends 1997). Amino acids are needed to
cover the metabolic nitrogen demand of heterotrophic organisms and are thus of
high qualitative importance.
The relative enrichment of THAA- (sum of the hydrolyzable amino acids) and
POC-contents in the mud layers of the Swinnplate compared to the reference site
in the sandtlat showed the intluence of mussels on the quality of organic matter
(Fig. 5.2.9). A seasonal pattern appeared with a moderate THAA-enrichment in
spring 1994 and 1995 and a fast increase in June (Behrends 1997). The enrichment
of POC by the filtration of the mussels was relatively higher than the enrichment
of THAA in the entire year of 1995. This was an indication for the selective consumption of amino acids by the mussels. The highest enrichment for POC was
found during a macroalgal cover in August 1995. However, this was not the case
for amino acids. It was concluded that a sedimentation of organic matter of lower
quality had occurred by passive deposition. In contrast to that, the relative enrichment of THAA and POC were almost identical after the disappearance of the mussel beds due to the ice winter in 1995/96 (Behrends 1997). This suggests that, on
the one hand, M. edulis reduced the quality of the organic matter and, on the other
hand, that the influence of other heterotrophic organisms on the composition of
organic matter is rather small.
The proportion of amino acid-carbon of total POC in the sediments of the mussel bed was clearly reduced in comparison to the sandflat sediments without mussels. This was also obvious from the lower enrichment of particulate amino acids
relative to POC in the mussel beds than in the sandflat (Fig. 5.2.9).
'; Spallal and Temporal Di,tnbutlOn Pattern,
plication of a two-component mixture model would lead to a marine proportion of
approx. 80 % in the surface sediment, which decreased to a proportion of approx.
20-25 % at 25 cm depth. This would indicate a preference for degradation of marine organic carbon.
A further characterization of the origin of marine organic matter (phytoplankton, macroalgae and other marine organisms) with organo-geochemical methods is
possible. For example, steroles are suitable to differentiate between the input of
macroalgae and diatoms into the sediment (Volkman 1986). Sterols are components of the cell membrane in all organisms except bacteria. Their different molecular structures permit a specific allocation to the source organisms, a modification of the structure indicates diagenetic processes. The comparison of the
concentrations of a steroid biomarker typical for diatoms (brassicasterol), with
those characteristic for macroalgae (fucosterol), indicated how these sources contributed to the composition of organic matter in the sediment over the year. The
results showed that an input of phytoplankton biomass into the sediment took place
in spring, while in autumn a macroalgal occurrence could be distinguished from a
following phytoplankton bloom (Brocks unpubl. data).
Effect of mussels on the quality of organic matter
The effect of blue mussels on organic matter could only be revealed when the
quality of this material was considered. The quality was assessed in samples taken
along the transect on the Swinnplate which were analysed for the proportion of
amino acids on the POc. In an additional mesocosm experiment, the pigment
composition was determined also (Behrends 1997). Amino acids are needed to
cover the metabolic nitrogen demand of heterotrophic organisms and are thus of
high qualitative importance.
The relative enrichment of THAA- (sum of the hydrolyzable amino acids) and
POC-contents in the mud layers of the Swinnplate compared to the reference site
in the sandtlat showed the intluence of mussels on the quality of organic matter
(Fig. 5.2.9). A seasonal pattern appeared with a moderate THAA-enrichment in
spring 1994 and 1995 and a fast increase in June (Behrends 1997). The enrichment
of POC by the filtration of the mussels was relatively higher than the enrichment
of THAA in the entire year of 1995. This was an indication for the selective consumption of amino acids by the mussels. The highest enrichment for POC was
found during a macroalgal cover in August 1995. However, this was not the case
for amino acids. It was concluded that a sedimentation of organic matter of lower
quality had occurred by passive deposition. In contrast to that, the relative enrichment of THAA and POC were almost identical after the disappearance of the mussel beds due to the ice winter in 1995/96 (Behrends 1997). This suggests that, on
the one hand, M. edulis reduced the quality of the organic matter and, on the other
hand, that the influence of other heterotrophic organisms on the composition of
organic matter is rather small.
The proportion of amino acid-carbon of total POC in the sediments of the mussel bed was clearly reduced in comparison to the sandflat sediments without mussels. This was also obvious from the lower enrichment of particulate amino acids
relative to POC in the mussel beds than in the sandflat (Fig. 5.2.9).