:;2 HJ(l)!cochcmical Processes and Interactions
109
This effect was attributed to an enhanced remineralization of organic matter
during the summer months followed by Mn tluxes from the sediment. This interpretation was confirmed by the increase of dissolved phosphate concentrations in
the interstitial water during summer (Sect. 5.2.1.3) as well as by seasonal variations of microbial activity, which were related to temperature and phytoplankton
blooms.
Quality of organic matter
Coastal marine particulate organic matter (POC) consists for about 50 % of hardly
degradable humic substances, while the remaining 50 % are composed of more
easily degradable material: 10-15 % sugars, 5-10 % lipids and approx. 30 %
amino acids (Liebezeit, pers. comm.). To study the effect of organic matter on
sediment chemistry and macrobenthic distribution patterns, the determination of
just the quantity of organic matter alone is not sufficient. The quality of organic
matter can be defined from two perspectives: its source or its usefulness for other
orgalllsms.
Most authors define quality of organic matter as the availability or usefulness
(potential to degrade, energetic use or nutritional value) as food source for organisms. Thereby, labile (easily degradable) and more refractory (hardly degradable
or residual fraction) organic substances are distinguished often. This depends not
on the molecular size (high-molecular or low-molecular substance), but on the type
and stability of the bonds within the molecule. The evaluation of organic matter is
usually carried out by the analysis of lipids, carbohydrates, proteins and pigments.
In particular chlorophyll a and phaeopigments or fatty acids are used as substances
to indicate labile organic material.
Quality and oriRin
From another perspective, the quality of the organic matter is defined by its different sources. This implies the question about the origin of the material, which can
also be subject to seasonal tluctuations. In the context of the biomarker investigations, the fatty acid analyses showed only small proportions of terrestrial biomarkers and verified a predominant marine to estuarine origin of organic matter in the
sediments of the Swinnplate (Brocks unpub\. data).
At all transect sites, higher contents of bacterial fatty acids were present from
August to September than in spring (Brocks unpub\. data). While in spring and
summer seasonal variations of fatty acids may have obscured possible spatial
variations between the transect sites, clear differences existed in autumn between
the mussel sites and the sandtlat site.
The predominant marine origin of the organic matter could also be confirmed
by carbon isotope analysis. The 8
ll
C-values of the POC decreased continuously
with increasing sediment depth from approximately -19 %0 at the sediment surface
to -25 %0 at 25 cm depth (Bottcher unpub\. data). This may be explained by the
different speed of early diagenetic degradation of terrestrial and marine organic
matter. After Salomons & Mook (1981), particulate terrestrial organic carbon had
8
ll
C-values of -27,4 'ko. However, the fresh organic matter of marine origin from
the backbarrier area of Spiekeroog island had values between -16 and -18 %0. Ap-
109
This effect was attributed to an enhanced remineralization of organic matter
during the summer months followed by Mn tluxes from the sediment. This interpretation was confirmed by the increase of dissolved phosphate concentrations in
the interstitial water during summer (Sect. 5.2.1.3) as well as by seasonal variations of microbial activity, which were related to temperature and phytoplankton
blooms.
Quality of organic matter
Coastal marine particulate organic matter (POC) consists for about 50 % of hardly
degradable humic substances, while the remaining 50 % are composed of more
easily degradable material: 10-15 % sugars, 5-10 % lipids and approx. 30 %
amino acids (Liebezeit, pers. comm.). To study the effect of organic matter on
sediment chemistry and macrobenthic distribution patterns, the determination of
just the quantity of organic matter alone is not sufficient. The quality of organic
matter can be defined from two perspectives: its source or its usefulness for other
orgalllsms.
Most authors define quality of organic matter as the availability or usefulness
(potential to degrade, energetic use or nutritional value) as food source for organisms. Thereby, labile (easily degradable) and more refractory (hardly degradable
or residual fraction) organic substances are distinguished often. This depends not
on the molecular size (high-molecular or low-molecular substance), but on the type
and stability of the bonds within the molecule. The evaluation of organic matter is
usually carried out by the analysis of lipids, carbohydrates, proteins and pigments.
In particular chlorophyll a and phaeopigments or fatty acids are used as substances
to indicate labile organic material.
Quality and oriRin
From another perspective, the quality of the organic matter is defined by its different sources. This implies the question about the origin of the material, which can
also be subject to seasonal tluctuations. In the context of the biomarker investigations, the fatty acid analyses showed only small proportions of terrestrial biomarkers and verified a predominant marine to estuarine origin of organic matter in the
sediments of the Swinnplate (Brocks unpub\. data).
At all transect sites, higher contents of bacterial fatty acids were present from
August to September than in spring (Brocks unpub\. data). While in spring and
summer seasonal variations of fatty acids may have obscured possible spatial
variations between the transect sites, clear differences existed in autumn between
the mussel sites and the sandtlat site.
The predominant marine origin of the organic matter could also be confirmed
by carbon isotope analysis. The 8
ll
C-values of the POC decreased continuously
with increasing sediment depth from approximately -19 %0 at the sediment surface
to -25 %0 at 25 cm depth (Bottcher unpub\. data). This may be explained by the
different speed of early diagenetic degradation of terrestrial and marine organic
matter. After Salomons & Mook (1981), particulate terrestrial organic carbon had
8
ll
C-values of -27,4 'ko. However, the fresh organic matter of marine origin from
the backbarrier area of Spiekeroog island had values between -16 and -18 %0. Ap-