|Tidal freshwater habitat restoration through controlled reduced tide system: a multi-level assessment = Herstel van getijhabitat in de zoetwaterzone door middel van gecontroleerd gereduceerd getij: een evaluatie op meerdere niveaus|
Beauchard, O. (2012). Tidal freshwater habitat restoration through controlled reduced tide system: a multi-level assessment = Herstel van getijhabitat in de zoetwaterzone door middel van gecontroleerd gereduceerd getij: een evaluatie op meerdere niveaus. PhD Thesis. Universiteit Antwerpen: Antwerpen. ISBN 978-90-7028-948-5. 97 pp.
Getijdenomgeving; België, Schelde R. [Marine Regions]; Marien; Brak water; Zoet water
The worldwide extent of tidal wetlands has greatly decreased, primarily due to large-scale embankments for agricultural, industrial and urban developments. Such pressures have resulted in narrowing estuarine corridors and in increasing shear stress on the remaining estuarine habitats. Concomitantly, the increased mean high water level has constrained ecological restoration in adjacent embanked areas. The inability to create an adequate tidal regime in embanked areas is a major problem for restoring estuarine habitats. A new restoration technique, the controlled reduced tide system (CRT), was hypothesized to overcome this constraint. As part of a management plan combining flood protection and tidal habitat restoration, the first CRT system was implemented in polder from the freshwater zone of the Schelde estuary (Belgium). In an interdisciplinary context, this work focuses on different ecosystem compartments and interactions in order to assess the coherence between abiotic and biotic components and to appraise the relevance of further wide applications in tidal wetland restoration. Within four years following the connection of the polder to the estuary, different ecosystem compartments and processes were studied: hydrology, sediment physicochemical characteristics, and invertebrate and bird communities. Despite some slight deviances from the reference, the tidal characteristics generated by the CRT technique were suitable with a clear reproduction of the spring-neap tidal cycle. This soft hydrology led to the formation of a finegrained estuarine sedimentary substrate in the most frequently flooded zones, contrasting with estuarine sand flats. Biogeochemical services such as sediment trapping and nutrient burial were demonstrated. These new environmental conditions were shown to be more suitable to sediment invertebrate community development than those encountered in reference sites from the adjacent estuary. CRT habitats displayed enriched communities, especially with epibenthic organisms. Divergence in community functioning was explored by confronting environmental characteristics and organism’ biological attributes. In a comparative way, the shear stress exerted on the estuarine tidal flats was assumed to be the main explanation to the faunistic impoverishment at a high flooding frequency. Additionally, specific bioturbative modes were identified along the CRT flooding frequency gradient. From organism to environment, this underlines potential ecological feed-back and implications in estuarine biogeochemistry. At higher trophic levels, 103 bird species were inventoried, encompassing a dominant part of characteristic wetland species, among which 38 exhibited local and/or international concern. Communities were found to be strongly habitat specific and non-randomly organized across habitats. From ground to foliage, habitat occupancy was found to be consistent with species functional abilities over the whole seasonal cycle. Globally, the avifauna positively responded to CRT habitat creation since communities were composed of a large majority of generalist and specific birds typical of European freshwater wetlands. Significant relations were found among the different ecological compartments. Conclusively, the results emerging from this work provide evidence for the potential of the CRT technique in rapidly creating a diversified tidal freshwater ecosystem. The restoration potential of this restoration technique is shown to be particularly relevant for tidal marshes in early succession stage, habitats which often lack in embanked estuaries.