242
l) Stability Propertlcs In the Waddcn Sea
mary production of the microphytobenthos). The tides ensure that these processes
can take place because they enable the diffusion of oxygen from the air during low
tide, as well as turbation caused by tidal currents. Another mechanism which is
relevant for the oxic layer seems to be storms.
Bacteria are mainly responsible for the resilience of the oxic layer to locally increased amounts of dead organic matter. If they were not able to switch to anaerobic metabolism, the decomposition of organic matter would be incomplete and the
oxic layer would not be re-established. Thus, the resilience and, in turn, the persistence of the oxic layer rely not only on physical and chemical processes, but
also on biotic activities.
Extreme scenarios
The scenario of an enduring anoxic intertidal with a rotten odour of hydrogen sulphide and where only bacteria can survive is - under natural conditions - very
unlikely. The risk of collapsing to lasting anoxic conditions, which exists for more
static waters like lakes or lagoons in warmer climates, does not threaten the Wadden Sea because of the tides which move the water, facilitating the diffusion of
oxygen from the air during low tide, and ensuring the input of oxygen-rich water
from the North Sea into the Wadden Sea. However, the massive anthropogenic
input of nutrients or toxicants or even a major oil tanker disaster would considerably increase the regeneration time of the oxic layer (Kuiper et a!. 1984).
9.4.4 Summary: Abiotic Ingredients of the Wadden Sea
The attempt to assess the stability properties of the abiotic ingredients of the Wadden Sea revealed in almost all cases the same pattern: on a short time scale (from a
few days to a year) and in small areas - low constancy (or high unpredictability);
on an intermediate time scale (years to several decades) and larger areas - constancy; and on a large time scale (several decades to centuries) and for the entire
Wadden Sea - slow and continuous change which, however, under natural conditions does not alter the persistence of the Wadden Sea, i.e. the essential properties
of a landscape shaped and determined in all respects by the tides.
This general pattern forms the background for all following assessments of the
stability properties of the biotic ingredients of the Wadden Sea. In particular, reference dynamics can only be specified for intermediate temporal and spatial scales.
We tried to demonstrate that the tides do not only shape the landscape but are
also responsible for the stability properties of three key ingredients of the Wadden
Sea: the existence of extended tidal flats, which is the result of an interplay between tides, historical sea level rise, the flat morphology of the coast, and sedimentation; the characteristic morphology of the Wadden Sea; and the existence
and resilience of an oxic layer on the sediment surface.
l) Stability Propertlcs In the Waddcn Sea
mary production of the microphytobenthos). The tides ensure that these processes
can take place because they enable the diffusion of oxygen from the air during low
tide, as well as turbation caused by tidal currents. Another mechanism which is
relevant for the oxic layer seems to be storms.
Bacteria are mainly responsible for the resilience of the oxic layer to locally increased amounts of dead organic matter. If they were not able to switch to anaerobic metabolism, the decomposition of organic matter would be incomplete and the
oxic layer would not be re-established. Thus, the resilience and, in turn, the persistence of the oxic layer rely not only on physical and chemical processes, but
also on biotic activities.
Extreme scenarios
The scenario of an enduring anoxic intertidal with a rotten odour of hydrogen sulphide and where only bacteria can survive is - under natural conditions - very
unlikely. The risk of collapsing to lasting anoxic conditions, which exists for more
static waters like lakes or lagoons in warmer climates, does not threaten the Wadden Sea because of the tides which move the water, facilitating the diffusion of
oxygen from the air during low tide, and ensuring the input of oxygen-rich water
from the North Sea into the Wadden Sea. However, the massive anthropogenic
input of nutrients or toxicants or even a major oil tanker disaster would considerably increase the regeneration time of the oxic layer (Kuiper et a!. 1984).
9.4.4 Summary: Abiotic Ingredients of the Wadden Sea
The attempt to assess the stability properties of the abiotic ingredients of the Wadden Sea revealed in almost all cases the same pattern: on a short time scale (from a
few days to a year) and in small areas - low constancy (or high unpredictability);
on an intermediate time scale (years to several decades) and larger areas - constancy; and on a large time scale (several decades to centuries) and for the entire
Wadden Sea - slow and continuous change which, however, under natural conditions does not alter the persistence of the Wadden Sea, i.e. the essential properties
of a landscape shaped and determined in all respects by the tides.
This general pattern forms the background for all following assessments of the
stability properties of the biotic ingredients of the Wadden Sea. In particular, reference dynamics can only be specified for intermediate temporal and spatial scales.
We tried to demonstrate that the tides do not only shape the landscape but are
also responsible for the stability properties of three key ingredients of the Wadden
Sea: the existence of extended tidal flats, which is the result of an interplay between tides, historical sea level rise, the flat morphology of the coast, and sedimentation; the characteristic morphology of the Wadden Sea; and the existence
and resilience of an oxic layer on the sediment surface.