Paardenschor wetland - small scale brackish tidal wetland restoration in the Sea Scheldt (Zeeschelde)

Sediment characteristics

The sedimentation at the Paardenschor influenced the sediment composition over the years. After the restoration, grain size was much larger compared to the original intertidal flat (Figure 6). After three years, grain size was comparable on the restored and original intertidal flat. Parallel, silt content and content of organic material in the restored area were lower in the first years but increased gradually in the following years (Figure 7 & Figure 8).

Sediment quality

Immediately after the restoration of the Paardenschor the calculated scores for total pollution on the restored areas and the original mudflats were comparable (Brys et al. 2005) and did not change significantly over time (Speybroeck et al. 2011). The most heavily polluted samples were classified as “moderately polluted”.

Vegetation

Five years after restoration, the Paardenschor still consists mainly of bare mudflat. However, every year 3.6% of the intertidal flat became vegetated. Vegetation grows mainly at the edges of the mudflat and along the channels in development (Figure 9 & Figure 10). Common vegetation in 2009 was mainly Sea club-rush (Bolboschoenus maritimus or Scirpus maritimus) with on the higher parts also Creeping bentgrass (Agrostis stolonifera) and Common Reed (Phragmites australis) (Figure 11). At lower parts, in the direction of the bare mudflat, pioneer vegetation appears dominated by Sea Aster (Aster tripolium) or Vaucheria (Vaucheria spec.).

Macrozoobenthos

In an average sample of the Paardenschor, 57% mudshrimp (Corophium volutator), 19% earthworms (Oligochaeta) and 17% Ragworm (Nereis diversicolor) was found (Figure 12). Those three taxa determine 93% of the present macrozoobenthos. Other species that were also found are Cyathura carinata, Baltic tellin (Macoma balthica) and Heteromastus filiformis. The diversity in macrozoobenthos is really poor.
The biomass of macrozoobenthos is mainly determined by Ragworm (Nereis diversicolor) and also a little by mudshrimp (Corophium volutator) (Figure 12).

After the restoration of the Paardenschor, a density increase was identified both on the restored area (DO1-3) and on the original mudflat (DO4-5) (Speybroeck et al. 2011). Immediately after the restoration of the Paardenschor (during the first measurement campaign), almost no macrozoobenthos is present on the restored mudflat (Figure 13). This is followed by a strong increase both on the restored and the original mudflat (Van den Neucker et al. 2007, Speybroeck et al. 2011).

One outlier is visible on Figure 13 (red circle). The high density in the autumn of 2006 at location DO3 is due to the presence of Vaucheria sp. (dutch: Nopjeswier) at the sample location. High densities of living Oligochaeten can house in this weed. However, the presence of this weed is highly dynamic with the effect of large variation in Oligochaeten densities. Location DO3 is also highly dynamic as a consequence of the development and morphologic changes of a creek channel that developed only randomly at location DO3.
The evolution in biomass (Figure 13) is similar: steady increase in the new restored mudflat to a level of dynamic equilibrium. The first period after restoration shows however no initial peak compared to the evolution of the density. The density peak in combination with no biomass peak indicates a large amount of light and hence small young organisms. This is typical for young systems occupied by a large number of newcomers, followed by a density decrease but a steady asymptotic biomass evolution.

Avifauna

A total of 19 species of water birds were recorded at the Paardenschor (Table 1) (Van den Neucker et al. 2007). Common Shelduck (Tadorna tadorna), Mallard (Anas platyrhynchos), Curlew (Numenius arquata) and Oystercatcher (Haematopus ostralegus) were almost always observed. The restored site is used for foraging as well as roosting. Benthic invertebrates are abundant and the inundation time of the newly created mudflat is limited. Only few suitable breeding sites were available throughout the study period. The importance of the Paardenschor as a breeding ground is expected to increase as parts of it develop into tidal marsh.

Fish

No monitoring results available.