During the construction and operational phases of the Mittelplate, no significant influences on the Wadden Sea were discovered in either geomorphology investigations or pollution measurements. The only detectable effects on the geomorphology of the Mittelplate region resulted from the removal of sediment in the construction phase and the hydraulic flushing undertaken to dredge the port approaches in the following years. Compared to the natural changes in geomorphology, however, these changes are of little significance. From the examination of sediment for harmful substances, no evidence could be found for any pollution of the area under investigation.
Benthic organisms remain undisturbed
Organisms living on the seabed (benthos) in the immediate vicinity of the drilling island were examined in order to trace any possible influence arising from the activities there. The spatial distribution of the species and population density on the Mittelplate shows a close correlation with the natural conditions such as sediment particle size, the effect of current and the consequences of weather. There were no indications of any sustained effect on the benthos population resulting from the oil production island.
Bio-monitoring with the aid of common mussels
Bio-monitoring was carried out on common mussels between 1989 and 1995. This was used to check whether any pollutants from the Mittelplate get into the North Sea and accumulate in the mussels. The common mussels were placed in cages at a monitoring position in the vicinity of the island's wastewater discharge point, as well as at a reference position in the Wadden Sea.
No greater pollutant accumulation was detected at the monitoring position than at the reference position for any of the parameters investigated. There was thus no detectable pollution of the common mussels by the Mittelplate island, and hence nor of the North Sea.
Mittelplate has no effects on fish fauna
Further studies looked into the seasonal and spatial distribution of fish fauna in the vicinity of the Mittelplate, as well as the pattern of commercial fishing.
A total of 32 species were found, meaning that the variety of species is no different from that of other tidal mudflats in Schleswig-Holstein. There are a lot of plaice on the Mittelplate, using the Wadden Sea as a nursery area, and they are among the most important commercial fish species in the North Sea. However, the main catch in the inshore fishing industry is the North Sea shrimp. There were no perceptible reductions in yield for the shrimp fishery or other effects from the operation of the Mittelplate drilling island on the fish fauna, such as changes in stock levels or a shift in the composition of species.
Birds get used to the production facility as a permanent fixture
The spatial and seasonal distributions of migrant birds around the island have been investigated since the start of production in 1987 and the possible effects of oil production on the avian fauna have been described.
Bird counts prove that for some species of birds the conditions for an area “of international significance” are fulfilled for the wider area around the drilling and production facility. In the immediate vicinity of the Mittelplate itself the density of feeding birds is rather low. This can be attributed to the relatively low availability of edible material in the sandflat region, in comparison to tidal mudlflats. The distance that the birds maintain between themselves and the island seems to be continuously reducing. This shows that they are getting used to the permanent fixture. The impact on the birds of the drilling and production facility and the associated marine traffic is only slight and confined to a small area.
The results of the studies, which are still ongoing, prove that with the exception of the construction of the island there have been no lasting modifications to the pattern of natural changes on the tidal flats.