|Towards a simplification for estimating bioturbation intensities|
Blok, T. (2019). Towards a simplification for estimating bioturbation intensities. Thesis. NIOZ Royal Institute for Sea Research: Yerseke. 27 pp.
Increasing anthropogenic changes (e.g. reaching from local dredging to climate change) affect estuarine and coastal ecosystems which provide essential ecosystem services (e.g. coastal protection, nursery for species, loss of areas for migrating birds). In Zeeland, a province in the southwestern part of the Netherlands), the Delta works were built to prevent flooding of land at high tide. These constructions have changed the currents, hydrodynamics and morphology of the estuarine ecosystem surrounding Zeeland. To predict how these ecosystems will react to these changes, a better understanding of the benthic communities and their interaction and role within the environment is important. Bioturbation, the reworking of sediment by benthic fauna, is one of the most important processes for the functioning (e.g. distribution of food resources, creating new habitat in deeper horizons of the sediment, increasing biodiversity, enhancing nutrient cycling) of the estuarine ecosystems. Bioturbation can be of a local nature, where random displacement of particles occurs over very short distances, leading to an exponential decrease of food particles with depth. Bioturbation can also be of a non-local nature, with particles being reworked over longer distances in discrete steps, creating an increase in food resources below the sediment surface.In this study, different ecosystems around Zeeland (Western Scheldt, Eastern Scheldt and Grevelingen) were investigated in terms of bioturbation using vertical chlorophyll profiles. The distribution of local and non-local sediment mixing and bioturbation intensities were related to environmental parameters (e.g. macrofauna, food supply and salinity) in order to detect relationships.A study in the Baltic Sea (Morys et al. 2016) has shown an increase in non-local mixing with decreasing salinity. The same relation is visible in the Western Scheldt (unpubl. data). In the Baltic Sea, it seemed that the intensity of non-local mixing increases with increasing abundance of gallery-biodiffusors. In contrast, in the Western Scheldt, Eastern Scheldt and Greveingen an increase of non-local mixing with decreasing abundance of gallery-biodiffusor's was detected. Local sediment mixing was found to negatively correlate with surface chlorophyll concentration which represents the amount of food resources available of the macrofauna. In the estuaries of Zeeland (Eastern Scheldt and Grevelingen) a rather weak correlation indicates the same relationship of increasing local mixing with decreasing food supply. Further research why the bioturbation intensities are influenced differently in the various systems around Zeeland compared to the Baltic Sea is needed to provide further insight into how the estuarine ecosystems function and towards a simplification for estimating bioturbation intensities.