l)~
'i Spallal and Temporal Dlstnhulion Patterns
Further II1vestigations dealt with the pore water chemistry in naturally occurring
black spots (Hapner & Michaelis 1(94) and sandflat sediments experimentally
enriched with an overload of organic matter. The aim of these experiments was to
determine a critical level for the input of organic matter into intertidal sediments
and characteristic indicators for an excess of organic enrichments. The following
possible effects were considered: the loss of the oxic sediment surface layer, a
complete consumption of the sulphate in the pore water, toxic sulphide concentrations and increased methane emission. A further interest was to predict the regeneration ability of disturbed sediment surfaces to normal conditions.
The results of several studies carried out in close collaboration by a team of scientists in the ecosystem research project ELA W AT are summarized in the following sections. The investigations concentrated on two sites in the backbarrier system
of Spiekeroog, the Swinnplate and the Groninger Plate (Chap. 3.1). Of special
importance were the input of organic matter, the remineralization of this material
as well as spatial and temporal variations of the studied parameters. Microbial and
geochemical processes and their interactions with macrozoobenthos are considered
and discussed. The distribution of macrofauna under the influence of a mussel bed
on the Swinnplate is described in Sect. 5.2.2.
5.2.1.2
Swinnplate
For the investigations on the Swinnplate (SP), sediment samples were taken at
6 sites along a transect from the centre of a mussel bed (Mytilus edulis) to a reference site in the sandflat (Chap. 3.1; Fig. 3.1.3). At the beginning of the investigations in spring 1994, the sites SPI and SP2 were located in the area of the main
mussel settlement. As a reference, site SP6 was situated on the sandflat. The direction of the transect was adjusted to the tlow of the ebb current, with which the
material discharge from the mussel bed took place. Sampling was carried out in
intervals of one to two months. The range of methods applied covered the analysis
of parameters of organic and inorganic geochemistry as well as microbiology.
The surface sediments of the transect sites were studied in order to estimate the
influence of the mussel bed and temporal variations on the sediment composition.
The conditions on the Swinnplate changed severely during the study period under
the influence of weather and hydrodynamics. A larval spatfall in summer 1994
over the entire study area led to a new settlement of blue mussels south of SP5,
which remained relatively stationary over the year 1995. Biodeposits produced
there affected the reference site SP6. In August 1994 and 1995 macroalgae (Enteromorpha spp. and Ulva sp.) attached to the mussels on all sites. A summary of
special events as well as spatial and temporal variations at the transect sites during
the study period is given in Table 5.2.1.
Besides such single unpredictable events, the seasonal intluences on the sediments of the transect were determined. In this context, both biological and physical
variations had to be considered. The filtration activity of mussels varies with season (phytoplankton blooms) and the activity of microorganisms is in turn linked to
the supply of organic matter and the ambient temperature. Physical modifications
refer to wave energy, storms, temperature and further to the content of suspended
matter (Krage I 1997) and the proportion of fine-grained material in the surface
sediments (see Chap. 3.4).
'i Spallal and Temporal Dlstnhulion Patterns
Further II1vestigations dealt with the pore water chemistry in naturally occurring
black spots (Hapner & Michaelis 1(94) and sandflat sediments experimentally
enriched with an overload of organic matter. The aim of these experiments was to
determine a critical level for the input of organic matter into intertidal sediments
and characteristic indicators for an excess of organic enrichments. The following
possible effects were considered: the loss of the oxic sediment surface layer, a
complete consumption of the sulphate in the pore water, toxic sulphide concentrations and increased methane emission. A further interest was to predict the regeneration ability of disturbed sediment surfaces to normal conditions.
The results of several studies carried out in close collaboration by a team of scientists in the ecosystem research project ELA W AT are summarized in the following sections. The investigations concentrated on two sites in the backbarrier system
of Spiekeroog, the Swinnplate and the Groninger Plate (Chap. 3.1). Of special
importance were the input of organic matter, the remineralization of this material
as well as spatial and temporal variations of the studied parameters. Microbial and
geochemical processes and their interactions with macrozoobenthos are considered
and discussed. The distribution of macrofauna under the influence of a mussel bed
on the Swinnplate is described in Sect. 5.2.2.
5.2.1.2
Swinnplate
For the investigations on the Swinnplate (SP), sediment samples were taken at
6 sites along a transect from the centre of a mussel bed (Mytilus edulis) to a reference site in the sandflat (Chap. 3.1; Fig. 3.1.3). At the beginning of the investigations in spring 1994, the sites SPI and SP2 were located in the area of the main
mussel settlement. As a reference, site SP6 was situated on the sandflat. The direction of the transect was adjusted to the tlow of the ebb current, with which the
material discharge from the mussel bed took place. Sampling was carried out in
intervals of one to two months. The range of methods applied covered the analysis
of parameters of organic and inorganic geochemistry as well as microbiology.
The surface sediments of the transect sites were studied in order to estimate the
influence of the mussel bed and temporal variations on the sediment composition.
The conditions on the Swinnplate changed severely during the study period under
the influence of weather and hydrodynamics. A larval spatfall in summer 1994
over the entire study area led to a new settlement of blue mussels south of SP5,
which remained relatively stationary over the year 1995. Biodeposits produced
there affected the reference site SP6. In August 1994 and 1995 macroalgae (Enteromorpha spp. and Ulva sp.) attached to the mussels on all sites. A summary of
special events as well as spatial and temporal variations at the transect sites during
the study period is given in Table 5.2.1.
Besides such single unpredictable events, the seasonal intluences on the sediments of the transect were determined. In this context, both biological and physical
variations had to be considered. The filtration activity of mussels varies with season (phytoplankton blooms) and the activity of microorganisms is in turn linked to
the supply of organic matter and the ambient temperature. Physical modifications
refer to wave energy, storms, temperature and further to the content of suspended
matter (Krage I 1997) and the proportion of fine-grained material in the surface
sediments (see Chap. 3.4).