Hydro-ecological relations in the Delta Waters
Hydro-ecological relations in the Delta Waters Hydro-ecological relations in the Delta Waters
fn tidal water systems sedimentation and erosian of sediment continue above mean low waterlevel (KLW) and even mean high waterlevel (HXW). The lowest parts of the tidal zone have no vegetation except algae and some water plants (Zostera spec.). These tidal flats are m important feeding habitat for birds (Meire, et al. 1989). Some decimetres below MEW the ffrst smi-terrestrial vegetation starts to grow (Salicornia spec., Spartina spec.). This vegetation is usually inundated Cwice k day. %?hen accretion contintles to above MEW, vegetation develops to a variecy of plant communities. Geomarphology and vegeration of these higher salt marshes are much more difgerentiated than on the mud flats and the lower salt marshes. The above-mentioned pattern of succession (see also Fig. 1) represents the situation it! the sdine tidal are= of the South-West Netherlands. In the fresh and brackish tidal water systems this pattern is not essentially different, but there is a difference in vegetation types of the marshes (reed, rushes and willars). The constru~tian of the Delta Works reaulted ia an ewrmous chanse of the estnariae environment. In most areas a more or less fixed wacerlevel w s realized somewhat aound NAP (butcb Ordnanoe Level). The consequence was that the lmr parts of the tidal land were pennwently inundated, while the higher parts were hardly iufluenced by the flooding water. Large parts of the latter could develop as (semi-) natural ecosystms. Thfs development and ite future perspectives for nature conservatLon are the subjects of this paper. 2 ECOLllGICBI. DYNdMtCS I N VARIOUS WATERS The processes influencing the development of animal and plant communities cm be ordered in an hierarchical model (Fig. 2, derived from Bakker, et al. 1981). In this model the outer compartments dominate the inner ones. Though there is some influence in the opposite direction, this is of minor importance becsuse of its lower
Figure 3 Distribution of some estuarine marshland types in relation to 0 average chlorinity ( 100 CL-) . Open circles: salt marshes; black circles: brackish marshes with reed and rushes; hatched circles: fresh marshes with reed, rushes and willow coppices. This figure gives the situation before the construction of the Delta Works 1962 SWEOA MARITIMA Figure 4 Cyclic vegetation dynamics in a salt marsh after severe waterlogged conditions (after Beeftink. 1979)
- Page 49 and 50: 4 WAGBEET MEdSIIRaS TO PEEVBT OR LT
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Figure 3 Distribution of some estuar<strong>in</strong>e marshland types <strong>in</strong> relation to<br />
0<br />
average chlor<strong>in</strong>ity ( 100 CL-) . Open circles: salt marshes;<br />
black circles: brackish marshes with reed and rushes; hatched<br />
circles: fresh marshes with reed, rushes and willow coppices.<br />
This figure gives <strong>the</strong> situation before <strong>the</strong> construction of <strong>the</strong><br />
<strong>Delta</strong> Works<br />
1962 SWEOA MARITIMA<br />
Figure 4<br />
Cyclic vegetation dynamics <strong>in</strong> a salt marsh after severe<br />
waterlogged conditions (after Beeft<strong>in</strong>k. 1979)
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