Project part-financed by the European Union (European Regional Development Fund)

The Interreg IVB North Sea Region Programme

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Paddebeek wetland - small scale tidal wetland restoration in the freshwater zone of the Sea Scheldt (Zeeschelde)

Monitoring results

Geomorphology and topography

The global gradient of the Paddebeek wetland is 3.7% and constant during the monitoring period (Speybroeck et al. 2011). From the elevation profile we can conclude that only limited changes occurred in the elevation of the Paddebeek wetland (Figure 3). Three zones could be identified (Figure 3).
For the first zone with sederoplots PA1 and PA2, located at the terraces in the zone 0-12m from the reference point at the dike, no clear observations were made because the sample plots could not be found back every time and had to be replaced several times (Van den Neucker et al. 2007). In the second monitoring period, both plots were not monitored anymore (Speybroeck et al. 2011). Note that the flood risk is limited at both terraces (9% and 39% respectively) (Figure 3).
The central zone of the wetland (12-36m from the dike with plots PA3 and PA4) is flat with a river-oriented gradient of 0.5% and a gradual sedimentation rate of 4 to 6cm per year during the first monitoring period (Van den Neucker et al. 2007) and of approximately 2cm per year during the second monitoring period (Speybroeck et al. 2011).
Behind spot PA4 (behind 36m) the wetland is shaped by the remains of the old dike and is covered with rubble stone (Van den Neucker et al. 2007, Speybroeck et al. 2011). This resulted in a steep gradient of about 12% (Speybroeck et al. 2011).

Sediment characteristics

In addition to the limited geomorphological and topographical change, also the median grain size does not show a clear trend (Speybroeck et al. 2011). Despite a few outliers, the variation in the median grain size (and probably the sediment at total) mainly decreases in the upper centimeter (fraction 0-1cm). However, it is mainly a matter of erratic changes.
Location PA1 is rich in silt content with a median grain size mainly smaller than 60 µm, both in the upper (0-1cm) and deeper (0-10cm) fraction (Van den Neucker et al. 2007). The variation in the first six months after the construction was large (Figure 4). At location PA2, the median grain size decreased during the first three months after construction: from 170 to 105 µm in the upper fraction (0-1cm) and from 80 to 35 µm in the deeper fraction (0-10cm) (Figure 4) (Van den Neucker et al. 2007). After that, the median grain size increased again in both fractions. The sediment consisted mainly of fine sand.
Locations PA3 and PA4 are rich in silt content during the entire monitoring period with a median grain size, in both depth fractions, mainly smaller than 40 µm (PA3) and 50 µm (PA4) (Van den Neucker et al. 2007). From the end of 2005 at location PA3, the median grain size in the upper centimetre (0-1cm) was always a little smaller than in the deeper fraction (0-10cm) (Figure 4).

At locations PA1 and PA2, the organic matter concentration remained almost constant during the first year after the construction. At both locations, the concentration was low, always below 4% (Figure 5). In 2006, the concentration increased up to 5% in the deeper fraction (0-10cm). In the top fraction (0-1cm), the concentration increased even more but the variation was large (Van den Neucker et al. 2007).
At locations PA3 and PA4 the organic matter concentrations were higher but fluctuated during the first eight months around 4% (PA3) and 5% (PA4) (Figure 5) (Van den Neucker et al. 2007). After that, the concentration increased at both locations, mainly in the top fraction (0-1cm). And the increase was more intense at location PA3 which is probably related to the protected orientation of PA3 and the settlement of higher plants (Speybroeck et al. 2011).

Sediment quality

The global sediment quality (expressed in Triade score) remained constant over time with a triade score of 3 “moderately abnormal”. The main pollutants are mercury, PAHs and PCBs, followed by cadmium, copper and zinc (Speybroeck et al. 2011). The sediment quality is not really good at the Paddebeek wetland but is (almost) not affected by the sedimentation. However, the evolution to smaller sediment particles (clayish) causes a higher bioavailability of most pollutants with a negative impact on the general ecotoxicological condition of the Paddebeek wetland (Speybroeck et al. 2011).


In the fresh water part (Paddebeek) there were 6 vegetation types, which is much less than the 11 vegetation types in the brackish parts (Paardenschor and Ketenisse schor) (Van den Neucker et al. 2007). In general, the colonization at the Paddebeek is relatively slow as well as the turnover between different vegetation types. In contrast, at the brackish areas the colonization rate was also low but the turnover was high.

Until now, 140 species of macro-algae and higher plants and mosses were identified (Speybroeck et al. 2011). The willow wickers, used at the edge of the constructed terraces, are grown up to a shrub layer. The bare mud, developed between the terraces and the shoreline, is colonized by pioneer species like Vaucheria (Vaucheria sp.), Water-pepper (Polygonum hydropiper), Blue Water Speedwell (Veronica anagallis-aquatica subsp. Anagallis-aquatica), etcetera. Common Reed (Phragmites australis) colonised the pioneer vegetation and dominates now the entire zone between the terraces and the shoreline, except for a small area of bare mud. Further succession did not happen until now. This is possibly due to the gradual elevation by sedimentation (average elevation of the PQs between the terraces and the shoreline amounts 17 mm per year), but even more by the local hydrological conditions (groundwater drops only limited or not under the surface level). The presence of the shoreline limits the floods but also the drainage. However, the drainage is mainly limited by the compaction of the sediment and dumping of construction waste. At the more dynamic and exposed locations (PQ263), situated between the Sea Scheldt (Zeeschelde) and the shoreline, vegetation remains at pioneer stage with Water Pepper and Blue Water Speedwell (Veronica anagallis-aquatica).

Based on the flood frequency and the appearance of different vegetation types on the Paddebeek wetland, two zones can be distinguished: the lower elevation zone (with a flood frequency between 81 and 92%) which is mainly colonized by vegetation types 12, 13 and 14, and the higher elevation zones (with a flood frequency between 23 and 33%) which is mainly colonized by vegetation types 15, 16A and 16B (Figure 6). At the lower elevation zone, pioneer vegetation type 12 (Polygono-Veronicetum anagallidis-aquaticae) first colonized bare mud (type 17 “slik”) and then evolves to type 13 (Alismato-Scirpetum/Typho-Phragmitetum) and type 14 (rough Polygono-Veronicetum) (Figure 7 & Figure 8). At the higher elevation zone with only few estuarine influences, dry pioneer vegetation type 15 (Stellarietea mediae) changed to roughness type 16B (rough Circium vulgare) and sometimes also type 16A (rough Artemisia).


At the Paddebeek the monitoring of benthos was based on the Oligochaeta population because this wetland is situated in the fresh water zone of the Sea Scheldt (Zeeschelde). At Paddebeek low abundances of Oligochaeta were found immediately after restoration but they quickly increased significantly (Van den Neucker et al. 2007). Five different taxa of Oligochaeta could be distinguished with certainty at location PA3 and PA4 during the first monitoring period (May 2004-December 2005). In the Oligochaeta samples, also nine other taxa of benthos were identified (such as insect larva or pupal) and Acari, Collembola and Carychium (Van den Neucker et al. 2007).
At location PA3 no Oligochaeta were found immediately after the construction (May 2004), but the density increased afterwards (almost 125,000 individuals/m² in December 2004 and almost 100,000 individuals/m² in December 2005), see Figure 10. Tubificiden without hair were always dominant (Van den Neucker et al. 2007). The tubificiden without hair were mostly juveniles from the Limnodrilus-species (L. claparèdeianus, L. hoffmeisteri en L. udekemianus) and Tubifex blanchardi. At location PA4 low Oligochaeta densities (less than 4,000 individuals/m²) were found immediately after the construction (May 2004), mainly tubificiden with hair (Figure 9). The tubificiden with hair were mostly juveniles from T. tubifex. After May 2004, Oligochaeta was not sampled anymore at location PA4.

The Oligochaetataxa that were found at Paddebeek were representative for the freshwater zone of the Sea Scheldt (Zeeschelde) (Van den Neucker et al. 2007). The low number of benthos taxa that was found at Paddebeek is also not abnormal for this zone of the Sea Scheldt (Zeeschelde). Also on other wetlands in the area the number of species was comparable (Scheldedatabank INBO). The low species richness can be the consequence of the sometimes low oxygen concentration in the Upper Sea Scheldt (Boven-Zeeschelde) (Van Damme et al., 2005). Some species are known as opportunistic species (Tubifex tubifex, Limnodrilus-species and Quistadrilus) that can be found on places were oxygen supply is sometimes limited (Brinkhurst & Gelder, 1991).


Avifauna is not monitored in the Paddebeek.


The fish density in the creeks is very low. At the restoration site, only one carp (Cyprinus carpio), three roach (Rutilus rutilus) and two Three-spined stickleback (Gasterosteus acculeatus) were caught during one day (sample in 2007) (Van den Neucker et al. 2007). However, no data is available from the original mudflat to compare.

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