Anthropogenic effects on the macrozoobenthos in the ecosystem Wadden Sea off the industrial town of Esbjerg (Denmark) : Bachelor thesis

Institut für Geosysteme und Bioindikation
Schwenkler, Ronja

The anthropogenic effects on the ecosystem Wadden Sea at the coast of the industrial town of Esbjerg (Denmark) were studied using the macrozoobenthos as indicator organisms. Organism- and sediment samples were analyzed in order to deduce influences of Esbjerg Harbor, a wastewater treatment plant and other human activities. The number of species and abundances as well as sediment properties were compared to other studies in the trilateral Wadden Sea. As the idea of the study was initiated by current extension plans of Esbjerg Harbor, it was also attempted to estimate the approximate loss of organisms in case of an extension. Moreover, background information was obtained throughout interviews and newspaper articles. In total, 16 organism samples and 12 sediment samples were taken at five sampling locations: The Harbor (H), the Dam (D), the Bay (B) and the Wadden Sea (W, splitted in W1 and W2). Most species were found at the Bay and the Wadden Sea (W2). In total, 19 species were encountered which corresponds to the average in the trilateral Wadden Sea. Polychaete worms dominated the investigation area with about three-fourth of the total encountered organisms. The polychaetes Arenicola marina, Pygospio elegans and Scoloplos armiger were found at all four locations. The ecological quality (M-AMBI-Index) was found “good” on average by Azti’s AMBI program and did not differ much between the sampling locations. According to the disturbance analysis (AMBI-Index), species of AMBI disturbance type III were dominant in all samples, while the Bay showed the highest disturbance and the Dam was assessed to be least disturbed. The number of species at sampling locations W1 and W2 was tested significantly different by R. In this study, there was not proven a significant correlation of the number of species with any sediment parameters. The only correlation of the number of species was found with the disturbance and the ecological quality. At the Harbor, organisms tolerant to heavy contamination like heavy metals, tributyltin (TBT), organic enrichment, anoxia and H2S were found. The encountered species at the Dam featured tolerance for physical disturbance like tidal streams and wave exposure. They prefer high salinity and are intolerant for metals and nutrients. The Bay was inhabited by species that prefer brackish water. W was mostly influenced by H2S generation and W1 was probably also impacted by the percolate from a former waste deposit close by. The share of 17.5 % of AMBI disturbance-indicating species groups IV and V seemed to prove that the investigation area indeed was influenced by additional impacts compared to a study from 2010 in the UNESCO reserve. This supports the assumption that the investigation area could be influenced by anthropogenic effects due to its position close to the industrial area of Esbjerg. In comparison to other studies, the organic carbon content was quite low at most sampling locations, which could be explained by the coarse sediment. A quite low amount of biomass was found which goes along with comparably low densities of the different species. The mean total number of individuals was 1264 individuals per m2 (ind m-2) and the mean density of the species was 124 ind m-2. Compared to the period from 1989 to 1995, the density in the investigation area of the same encountered species had dropped to 45 %. Only 68 % of the average species number in the investigation area between 1987 and 1995 were encountered. This could reveal a significant loss, but one has to take into account that the number of samples was lower in the present study. The share that polychaetes contribute to the population had increased immensely since the former study, while molluscs had declined a lot. The samples of the Bay had an average fresh weight of 4.56 g organisms which can be projected to 257.5 t macroinvertebrates in the area of 1 km2 that will be taken from the tidal flats in case of a harbor extension. This potential loss in organisms could approximately be visualized by the food of 1058 oystercatchers for a whole year, assuming that 40 % of the prey is available for the birds. Even though a particularly negative impact of the harbor was not reflected in the number of
species and individuals compared to the other sampling locations in this study, the polychaete worms Capitella capitata and Heteromastus filiformis that can indicate heavy contamination were detected only at the sampling location in the harbor. This study shows a general anthropogenic impact on the investigation area, especially originating from a wastewater treatment plant and harbor drift, and losses in species and densities were detected. Alternative ways like dry harbors or space-saving improvements within the existing harbor area should be chosen instead of extending Esbjerg Harbor into the Wadden Sea area in order to protect the UNESCO World Heritage area from increasing impacts and losses in species.


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