Samenvatting

The Wadden Sea is the largest tidal area in the world and is of mayor importance in the sectors ecology, economy and culture. It was therefore added to UNESCO World Heritage Site in 2009. Hallumer-Ryt is an area in The Wadden Sea which is characterised by a saltmarsh. This habitat is considered to be a wetland type with a transitional character and has dynamic interactions between adjacent habitats in a natural state. A large spatial barrier is present in the landscape, in form of a dyke. This barrier is a factor which contributes to the reduction of the ecological potential of the saltmarsh and it adjacent habitats; the tidal flats and an inland area behind the dyke. A mayor consequence of the distinctive border between the saltmarsh and the inland area the appearance of hard boundaries between the previous gradual transition from a salt water to a fresh water ecosystem. In 2018, a pumping station and a fish ladder will be constructed in Hallumer-Ryt that may mitigate the transition between these ecosystems.
The goal of this research is to determine the current transition from a fresh water to a salt water ecosystem in Hallumer-Ryt. This is a necessary step before an assessment of ecological improvement can be made after the construction. Relations between the areas through biotic and abiotic indicator factors were researched in order to obtain knowledge on the current transition between the sub-areas: the tidal flats, saltmarshes and the inland area.
Biotic as well as abiotic factors were designated by literature and were studied in field and analysed subsequently. Fish and bird species distribution as well as physical parameters such as salinity, pH, oxygen temperature of surface water were key factors in this research. Other factors such as phytoplankton, benthos and chemical parameters were also included but not prioritised in the field operations and analysis. The distribution of the fish species was monitored using fish traps as well as fishing nets. Bird species, their location and their behaviour were monitored of four target species. Physical parameters were measured using the Hanna HI 9829 Multiparameter. The collected biotic data was analysed using Chi-Square Tests in IBM SPSS in order to find significant relations between factors and the sub-areas. This was done for abiotic data as well using One-way ANOVA Tests. Significance between a factor and the sub-areas is demonstrated when p = <0.050. The Jaccard Similarity Index was used on biotic factors in order to indicate the degree similarity between sub-areas.
Multiple biotic and abiotic factors were found to be indicators. Salinity and the distribution of fish species showed to have a direct relation because of the small variations in the sub-areas itself. pH and surface water temperature against the distribution of fish species showed a p = 0.00 in the Chi-Square Tests. These are all related indicator factors able to demonstrate the current transition from fresh to a salt water ecosystem between the sub-areas of Hallumer-Ryt.