Estuarine management and ecology: a case study on coastal defense and navigability
23 November 2016
In a new paper, Patrick Meire and Stijn Temmerman (UAntwerp) studied the long-term effects of human management in the Oosterschelde and the Westerschelde.
Estuaries – which are the most seaward part of rivers under the influence of tides - are often strongly human managed. Their geographic location makes them prime candidates for harbor infrastructure, and large populations nearby need to be protected against flooding. Hence, management often encompasses deepening of the waterway to allow ship travel, and construction of dikes and/or a storm surge barrier to prevent flooding calamities. At the same time, estuaries provide unique ecosystems that deliver valuable ecosystem services to society.
The long-term, large scale character of human management interventions causes a need to assess the impacts on the natural environment. In a new study, Stijn Temmerman and Patrick Meire (Global Change Ecology Centre, Research Group Ecosystem Management), together with their Dutch and Belgian colleagues, predict the long-term impact of human management practices on the natural environment in the Westerschelde and the Oosterschelde. They specifically focused on macrozoobenthic organisms. These are tiny animals, such as shellfish and worms that live on and within the sediment of estuaries.
The common cockle (Cerastoderma edule) and the Annelid worm Heteromastus filiformis (picture by Hans Hillewaert) are two examples of benthic estuarine species.
The Oosterschelde and Westerschelde are particularly interesting, as they represent case-studies for the effects of two large scale management options: a storm surge barrier in the Oosterschelde, and strong deepening of the channel for shipping purposes in the Westerschelde.
Patrick Meire: “We integrated empirical and modelling data on landscape morphology, hydrodynamics and benthic organisms’ ecology. Our analysis clearly shows the long-term implications of both forms of estuarine engineering. Deepening of the channel in the Westerschelde lead to an increase of tidal dynamics and stronger variations in salinity, which induces stress on the benthic community. In the Oosterschelde, the effect of the storm surge barrier was much more mixed. The Oosterschelde was transformed into a shallow, marine embayment. This actually induced an unexpected improvement of the environmental quality. The Oosterschelde now has a flourishing benthic community.”
These results clearly show the importance of long-term assessments of large human interventions in estuaries. Before the implementation of both the storm surge barrier and the deepening, the Oosterschelde and Westerschelde had similar current velocities and tidal dynamics. Within 50 years, both systems now have an incomparable ecological functioning.
Stijn Temmerman: “Our results clearly show that we should not only focus on direct, short-term impact assessments. We should put much more emphasis on the long-term effects on the natural environment. The divergent human pressures on the Oosterschelde and Westerschelde could happen in the near future for many estuaries worldwide. Therefore our analysis is a valuable source of information for coastal managers around the world”.
The results were published in the scientific journal Estuarine, Coastal and Shelf Science.
Aerial picture of the Oosterschelde and the Westerschelde. The storm surge barrier on the Oosterschelde is clearly visible, as is the port of Antwerp adjacent to the Westerschelde. Source: beeldbank.rws.nl, Rijkswaterstaat