5.2 Biogeochemical Processes and InteractIOns
113
energy content and a rejuvenation of the total organic matter in summer. The results are in good agreement with seasonal cycles of labile and refractable POC in
surface sediments reported from Kiel Bight (Graf et al. 1983).
Indications of the quality of organic matter from microbial parameters
The microbial investigations supplied indirect evidence of the quality of organic
matter. As part of these investigations, the RNA/DNA-ratio was analysed. This is a
parameter for the average protein synthesis activity of a population (Paul & Voroney 1984) which, apart from the AEC- value, supplies further information about
the fitness of the available biomass. A high RNA/DNA-ratio indicates an improved
fitness of the biomass, since the protein biosynthesis and thus the division activity
are high. This occurs when the cells have optimal growth conditions and are sufficiently supplied with nutrients.
In the seasonal development in the year 1995, an increase of the RNA/DNAratio was registered in June, followed by a collapse in summer from July to September and a second rise in October at the sites with mussel settlement (Albers
unpubl. data). While the RNA/DNA-ratio in the old and young mussel bed sediments showed a similar seasonal pattern, the reference site in the sandflat without
mussels hardly showed any seasonal fluctuation of this parameter at all.
The annual pattern of the RNA/DNA-ratio thus followed the typical seasonal
development of the phytoplankton with a temporal delay of 1-2 months. However,
the results can be biased by the sampling frequency, since fresh organic matter can
be degraded within 4 weeks (see above).
Furthermore, the relation of the exoenzyme activities (glucosidase, protease,
phosphatase) supplied indirect evidence of the composition of organic matter.
While a high activity of protease indicated an increased protein content of the
substrate and thus a good food quality, a high activity of glucosidase showed the
presence of high-molecular sugars (low food quality). Only once after the ice
winter and in contrast to the results from all other sampling dates, the activity of
glucosidase was higher than the activity of protease.
Conclusion
The origin of the organic matter of the Swinnplate was characterized mainly by the
input of material from marine and estuarine sources. The absolute POC-quantities
were highest within and around the mussel bed, due to the filtration activity and
the reduced current velocities by the epibenthic structure. The values decreased
with increasing distance from the mussel bed. A gradient from the mussel bed into
the sandtlat resulted from the export of fine-grained material with the ebb current.
The amount of deposited fine-grained material varied with the seasonal dynamics
of phytoplankton, which could be confirmed by specific biomarkers in the sediment. The deposition of the organic matter through the filtration by the mussels
was rapidly detectable in the sediment by increased contents of amino acids and
lipid-biomarkers, whereas the reaction of microbial parameters was delayed. Seasonal variations were also found in the energy contents of the sediments with high
values in summer and autumn. These fluctuations were also brought into connection with the input of fresh organic matter from phytoplankton blooms. Inspite of
113
energy content and a rejuvenation of the total organic matter in summer. The results are in good agreement with seasonal cycles of labile and refractable POC in
surface sediments reported from Kiel Bight (Graf et al. 1983).
Indications of the quality of organic matter from microbial parameters
The microbial investigations supplied indirect evidence of the quality of organic
matter. As part of these investigations, the RNA/DNA-ratio was analysed. This is a
parameter for the average protein synthesis activity of a population (Paul & Voroney 1984) which, apart from the AEC- value, supplies further information about
the fitness of the available biomass. A high RNA/DNA-ratio indicates an improved
fitness of the biomass, since the protein biosynthesis and thus the division activity
are high. This occurs when the cells have optimal growth conditions and are sufficiently supplied with nutrients.
In the seasonal development in the year 1995, an increase of the RNA/DNAratio was registered in June, followed by a collapse in summer from July to September and a second rise in October at the sites with mussel settlement (Albers
unpubl. data). While the RNA/DNA-ratio in the old and young mussel bed sediments showed a similar seasonal pattern, the reference site in the sandflat without
mussels hardly showed any seasonal fluctuation of this parameter at all.
The annual pattern of the RNA/DNA-ratio thus followed the typical seasonal
development of the phytoplankton with a temporal delay of 1-2 months. However,
the results can be biased by the sampling frequency, since fresh organic matter can
be degraded within 4 weeks (see above).
Furthermore, the relation of the exoenzyme activities (glucosidase, protease,
phosphatase) supplied indirect evidence of the composition of organic matter.
While a high activity of protease indicated an increased protein content of the
substrate and thus a good food quality, a high activity of glucosidase showed the
presence of high-molecular sugars (low food quality). Only once after the ice
winter and in contrast to the results from all other sampling dates, the activity of
glucosidase was higher than the activity of protease.
Conclusion
The origin of the organic matter of the Swinnplate was characterized mainly by the
input of material from marine and estuarine sources. The absolute POC-quantities
were highest within and around the mussel bed, due to the filtration activity and
the reduced current velocities by the epibenthic structure. The values decreased
with increasing distance from the mussel bed. A gradient from the mussel bed into
the sandtlat resulted from the export of fine-grained material with the ebb current.
The amount of deposited fine-grained material varied with the seasonal dynamics
of phytoplankton, which could be confirmed by specific biomarkers in the sediment. The deposition of the organic matter through the filtration by the mussels
was rapidly detectable in the sediment by increased contents of amino acids and
lipid-biomarkers, whereas the reaction of microbial parameters was delayed. Seasonal variations were also found in the energy contents of the sediments with high
values in summer and autumn. These fluctuations were also brought into connection with the input of fresh organic matter from phytoplankton blooms. Inspite of