Estuarine restoration: how to adapt our estuaries to global change? Are nature based solutions the Holy Grail?
Estuaries are among the most productive ecosystems delivering many ecosystem services but have suffered greatly from many anthropogenic pressures. Worldwide many estuaries are now heavily degraded due to habitat loss and pollution. In response many measures were taken to restore these systems. Apart from some exceptions, restoration was mainly driven by legislation. Thanks to environmental legislation emissions from both industries and households were reduced. In Europe the Bird and especially the Habitat directive and in the US the Estuary Restoration Act were a major driver for habitat restoration. Loss of habitat due to human activities such as harbor developments, must be compensated by creating/restoring similar habitat to achieve a net zero loss of habitat. Also the directives require the designed habitats to remain in a good state of conservation which is defined in surface and quality of different habitats and populations of species. This might also require restoration measures. As a consequence since a few decades a large number of restoration projects have been implemented. However the success of all these efforts is not always clear. We still see water quality problems and restored habitats do not always perform as expected. In the meantime further developments such as harbour development, fairway maintenance and especially climate change and sea level rise are likely to further impact our estuaries and challenge all management measures taken.
In this symposium we want to present the results obtained in the Schelde estuary and bring together worldwide experience on estuarine restoration and application of nature based solutions to discuss the scientific, legal and societal challenges of restoring estuaries and developing strategies to adapt our estuaries towards the expected climate change. We focus on the entire estuarine gradient from the upper estuary, the fresh water tidal area via the brackish zone towards the marine part in the lower estuary, extending in the mouth of the estuary.
The following sessions are planned:
| 1) | Restoring the pelagic habitats |
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A healthy estuary depends on a good water quality. In the past decades enormous investments were made worldwide in water purification. However still some major water quality issues remain, among them, still low oxygen concentrations, increasing suspended sediment concentrations, a whole series of emergent pollutants etc. This immediately impacts primary productivity and the pelagic ecosystem from phyto- over zooplankton to the fish populations. Also the hydrodynamics are changing in response to changing fresh water discharge, sea level rise and geomorphological changes. In this session we invite papers describing long term trends in water quantity and quality, primary production and pelagic biota (plankton, fish, hyperbenthos,..) emphasizing trajectories of change over time and insights on possible future changes due to global and climate change. Also papers on the interaction between the pelagic habitat and the input of the catchment and the benthic-pelagic coupling are welcomed. | |
| 2) | Restoring intertidal habitats |
The majority of restoration projects involve restoring tidal marshes and different techniques or nature based solutions are used. We invite papers documenting and evaluating the (long term) development of different restoration projects based on either different biota and or abiotic changes (sedimentation rate, sediment characteristics,…). Apart from the structural aspects we specially welcome papers documenting the functioning of these habitats, among others their geochemical functioning (impact on water quality), nursery function, carbon sequestration, primary production,.. Also restoration of benthic communities both inter- as subtidal in relation to improved water quality is an important topic as well as benthic-pelagic coupling. Did the projects deliver the predicted biota, the ecosystem services? What were the critical success/failure factors. How important are ecological engineers? | |
| 3) | How to plan for restoration, define objectives, goals? |
We can derive a lot of understanding from the past but still major knowledge gaps exist on planning the further restoration of estuaries. First of all how do we define the goals we want to achieve. Some are fixed in environmental legislation (water quality parameters, some biota,..), but many more need to be specified. For which parameters we should formulate goals (drivers of the system)? This can be among others primary production, nutrient ratio’s, an amount of different ecosystem services,… How these objectives should be defined and how can we translate the objectives into an coherent plan delivering the objectives. What is the surface of different habitats needed to deliver the requested goals? What is the optimal combination and spatial configuration of different projects to deliver the requested goals? What are the possibilities and limitations of modelling to estimate the impact of different scenario’s? How can we upscale from individual restoration projects to an estuary wide plan? Can we move from a pattern based to a process based restoration? | |
| 4) | Dynamic ecosystems versus static regulation |
Environmental legislation is essential as a legal basis for restoring our estuaries. However a conflict may arise between the dynamics of the estuarine ecosystem due to continuous geomorphological changes leading to changes in habitat distribution and the fixed conservation objectives. In this session we want to explore the possibilities to reconcile the inherent dynamic nature of estuaries with more stringent regulation. | |
| 5) | Evaluation and monitoring |
Monitoring is of crucial importance to document the changes in our estuaries however, unfortunately very often monitoring programs are reduced to budget reasons and restricted to what is required by legislation. A more holistic approach is needed and we welcome contributions on the set up of monitoring programs, including the possibilities of recent technological developments. Monitoring is one thing, analyzing the large data sets (especially from continuous measurements) and evaluating the results is another thing. How do we evaluate certain trends? When should the deviation of a parameter from some preset value trigger action? How do we combine the evaluation of the many measured parameters into an overall evaluation. Is the approach of the Water Frame Work directive, one out all out a useful approach? This and many related questions can be discussed in this session. |
Overall, we encourage papers to include where possible (not limitative) restoration techniques (different types of nature based solutions); quantification of ecosystem services (carbon sequestration, nursery function, storm flood protection,..); microbial communities; invasive species; new technologies, ideas of the way ahead, both concerning legislation, management,….