IIX
5 Spallal and Temporal Distnhutllll1 Patterns
Conclusions
On the basis of the obtained results different scenarios were described, which
could be regarded as diagnozing criteria for surpassing a critical level of organic
input into intertidal sediments. Among these were:
• the occurrence of black spots at the sediment surface
• an increased release of trace gases (e.g. CH 4 , H 2 S) from the sediment
• the appearance of anoxic bottom water
• lack of bioturbation activity
• exhaustion of the buffer capacity of the sediments for sulphide (approx.
3 mmol dm')
• the accumulation of DOC in the pore water. While a value of approx. 10 mg
dm' DOC is typical for unpolluted sediments, values of up to 4000 mg dm'
DOC were measured in the experimental sites.
After the start of an enrichment experiment, the pore water concentrations increased in the sequence DOC, methane, sulphate(decrease), phosphate, sulphide,
ammonia and decreased in the order DOC, sulphate(increase), ammonia, phosphate, sulphide again. The duration of the regeneration period depended on the
degree of the load (concentration of the buried organic matter). The time requirement for sediment regeneration in the experimental sites was approximately one
year, with the exception of the most heavily loaded site. However, from the
mathematical model there were some indications that an increased sensitivity towards a renewed load (exhaustion of the sediment sulphide buffer capacity) can
remain after the regeneration.
5.2.2
Distribution of Macrofauna Along the Transect
5.2.2.1
Introduction
The distribution pattern of benthic communities depends, among other factors, on
physico-chemical sediment parameters and is subjected to modifications of POCand mud contents. The classic model of Pearson & Rosenberg (1978) describes the
succession of macrofauna due to POC-enrichment by organic pollution. An analogous distribution was found by Dittmann (1987) in sediments with experimental
enrichments of biodeposits of the blue mussel Mytilus edulis, demonstrating that
biodeposits can be a structuring factor for benthic communities. Her experiments
showed that differences in the concentration of biodeposits influenced the smallscale distribution of benthic organisms.
In the context of ELA W AT, studies were carried out along a gradient with decreasing contents of mussel biodeposits. In order to examine the influence of the
biodeposits of a natural mussel bed on the sediment chemistry as well as the subsequent interactions between physico-chemical parameters and the organisms,
biogeochemists and benthologists collaborated at a common study site on the
Swinnplate (Fig. 3.1.3). The filtration and deposition of organic matter by the
mussels, its mineralization as well as its role in the structuring of microorganism
5 Spallal and Temporal Distnhutllll1 Patterns
Conclusions
On the basis of the obtained results different scenarios were described, which
could be regarded as diagnozing criteria for surpassing a critical level of organic
input into intertidal sediments. Among these were:
• the occurrence of black spots at the sediment surface
• an increased release of trace gases (e.g. CH 4 , H 2 S) from the sediment
• the appearance of anoxic bottom water
• lack of bioturbation activity
• exhaustion of the buffer capacity of the sediments for sulphide (approx.
3 mmol dm')
• the accumulation of DOC in the pore water. While a value of approx. 10 mg
dm' DOC is typical for unpolluted sediments, values of up to 4000 mg dm'
DOC were measured in the experimental sites.
After the start of an enrichment experiment, the pore water concentrations increased in the sequence DOC, methane, sulphate(decrease), phosphate, sulphide,
ammonia and decreased in the order DOC, sulphate(increase), ammonia, phosphate, sulphide again. The duration of the regeneration period depended on the
degree of the load (concentration of the buried organic matter). The time requirement for sediment regeneration in the experimental sites was approximately one
year, with the exception of the most heavily loaded site. However, from the
mathematical model there were some indications that an increased sensitivity towards a renewed load (exhaustion of the sediment sulphide buffer capacity) can
remain after the regeneration.
5.2.2
Distribution of Macrofauna Along the Transect
5.2.2.1
Introduction
The distribution pattern of benthic communities depends, among other factors, on
physico-chemical sediment parameters and is subjected to modifications of POCand mud contents. The classic model of Pearson & Rosenberg (1978) describes the
succession of macrofauna due to POC-enrichment by organic pollution. An analogous distribution was found by Dittmann (1987) in sediments with experimental
enrichments of biodeposits of the blue mussel Mytilus edulis, demonstrating that
biodeposits can be a structuring factor for benthic communities. Her experiments
showed that differences in the concentration of biodeposits influenced the smallscale distribution of benthic organisms.
In the context of ELA W AT, studies were carried out along a gradient with decreasing contents of mussel biodeposits. In order to examine the influence of the
biodeposits of a natural mussel bed on the sediment chemistry as well as the subsequent interactions between physico-chemical parameters and the organisms,
biogeochemists and benthologists collaborated at a common study site on the
Swinnplate (Fig. 3.1.3). The filtration and deposition of organic matter by the
mussels, its mineralization as well as its role in the structuring of microorganism