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|KRW doelstellingen in de Ijzermonding: Afleiden en beschrijven van typespecifiek maximaal ecologisch potentieel en goed ecologisch potentieel in het Vlaams waterlichaam 'Havengeul Ijzer' vanuit de - overeenkomstig de Kaderrichtlijn Water - ontwikkelde relevante beoordelingssystemen voor een aantal biologische kwaliteitselementen|
|Speybroeck, J.; Breine, J.J.; Vandevoorde, B.; Van Braeckel, A.; Van den Bergh, E.; Van Thuyne, G. (2008). KRW doelstellingen in de Ijzermonding: Afleiden en beschrijven van typespecifiek maximaal ecologisch potentieel en goed ecologisch potentieel in het Vlaams waterlichaam 'Havengeul Ijzer' vanuit de - overeenkomstig de Kaderrichtlijn Water - ontwikkelde relevante beoordelingssystemen voor een aantal biologische kwaliteitselementen Rapport van het Instituut voor Natuur- en Bosonderzoek, R.2008.55 Instituut voor Natuur- en Bosonderzoek: Brussel|
|Deel van: Rapport van het Instituut voor Natuur- en Bosonderzoek. Instituut voor Natuur- en Bosonderzoek: Brussel, meer|
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The European Water Framework Directive came into effect December 2000 in all member states. According to this directive, all European waters should reach ‘good status’ by the end of 2015. In order to assess the ecological status of their surface waters, member states have to act in concordance to a well-established step-wise plan and have to develop monitoring programs and valuation systems for a number of biological quality elements, which have been specified for each water category.
This report deals with step 3 (delimitation of a reference) and step 4 (development of a score system) for the Ijzer estuary. Subsequently, the ecological status is assessed. Assessed biological quality elements are macrophytes, benthic invertebrates and fish. This research elaborates for the water body “havengeul Ijzermonding” on the work of earlier study (Van Damme et al., 2003; Brys et al., 2005).
All Flemish transitional waters have been identified as heavily modified water bodies. Therefore, maximum and good ecological potential (MEP/GEP) set the reference goals, not pristine conditions. These MEP and GEP were defined from an ecosystem perspective as an optimal functioning estuarine ecosystem. Thus, the ecological potential is conceived as the potential for natural physical, chemical and biological processes to deploy as good as possible within certain (achievable) boundaries. Attaining this potential requires an approach that surpasses the local level and individual quality elements. Therefore, an integrated, hierarchical and scale-dependent approach was chosen to establish the reference framework, including essential habitat characteristics besides the biological quality elements.
At the ecosystem level, habitat area was considered, as it is a parameter relevant to all biological quality elements. Surface area of mudflats, salt marshes and subtidal habitats was also used to assess the hydromorphological status of the Ijzer estuary. To obtain the MEP, a hydromorphological approach was used. Threshold band width was calculated as a quantifier for the space that is needed to maintain typical estuarine habitats (mudflats, salt marshes and shallow subtidal areas) in a sustainable and dynamic equilibrium of sedimentation and erosion. Along the estuary, this ‘equilibrium band width’ is proportional to the elevation range difference between the channel bottom and the mean high tide level (MHW) and the mean highest high water level (MHHW). The GEP for mudflats and shallow subtidal habitats is deducted from the MEP, as done by Brys et al. (2005). The salt marsh GEP is obtained through the so-called Prague method, anticipating already proposed and/or planned measures for creation of estuarine habitats. The hydromorphological status of the Ijzer estuary is bad.
Phytoplankton was not considered. Under the natural environmental conditions in the estuary, the development of stable estuarine populations is not possible.
The macrobenthos metric consists of parameters at two scale levels:
- habitat level: mudflat and shallow subtidal area
- community level: BEQI (species richness, species composition, biomass and density)
These submetrics are subsequently integrated into a single indicator value (score). Given available data, the Ijzermonding obtain a ‘moderate’ score.
The macrophyte metric contains two levels:
- individual marsh level: (i) current area versus desired area (GEP) required for a sustainable development and conservation of the existing salt marshes, (ii) vegetation diversity, (iii) species richness and (iv) floristic quality index (FQI).
These submetrics are subsequently integrated into a single indicator value (score), whereas the submetric values allow specific identification of bottlenecks and mitigating measures. The Ijzermonding macrophytes are scored as ‘bad’.
Submetrics for the assessment of fish are selected based on their discriminating power. The presence reference list of Breine et al. (2008 – GEP reference list) is used. The fish fauna of the Ijzermonding scored ‘moderate’. Thus, applying the WFD principle ‘one out, all out’, the Ijzermonding’s final score is ‘bad’. Some suggestion for improvement are discussed.