Hydro-ecological relations in the Delta Waters

this volume or in Duutsaa, et aL, 1982. The situation is descriBed up
to 1984 since the data on birds presented in thia paper are restricted
to the period 1976-1984.
The major physical and chemical characteristics of the afferent basins
are given in Table 1. For each OS the tidal areas, the surface of
salt marshes, tidal flats, tidal waters (the area permanently covered
by water) and adjacent wetlands (creeks, "inlagen" and grasslands which
are used by birds either as resting or as additivnal feediqg sites) is
given. For tbe lakes the surface of deep water ( > 1.5 m), @hallow
wager ( 1.5 m) and sbwes is given. Shores are the very shallow areas
( F 0.2 m) of the lake of the majority of the areas perraanently exp~sed
after the fomatlon of the lake and now used by weterbirds
Kagrieultural land, nature reserve etc.) as well as the adjacent
wetlands.
The Voordelta is that part of the North Sea just off the Delta area. It
consists bf a system of chwnels and shallow areas. Salintry atrd
turbidity are high. The sandy beaches are subject to hem wave action
and su£fer from a very high ~ecreation pressure. More details of thia
area and the changes occurring here ate described by Mulder, 1989. The
Westerschelde is the only rema*ning true estuary in the Delta. The
freshwater input frqm the river Schelde is small (on average 100
m3/sec), hence the braokish part is limited to the area beMwn
Ancwerpen and Hansweert. From the mouth tmards Antwerpen a gradient of
decreasing salinity, oxygen and transparency. and of inereasing
suspended meter and nutrients is found (Humel, et al, 19881. Large
mid- and sandflats occur all over the eatuary. "Bet Verdronken Land van
Saeftinghe". in the brackish part BE the estuary, i5 the largest salt
marsh (8250 ha) of the whole Delta area. The esnurry is characterized
by a large anthropogenic stress due to discharges of inorganic and
organic eontamfnants, mfnly by the river Sahel.de, but alsa from othar
effluenrs slew the Westerschelde itself, and due to intensive dredging
activities for shipping. In the Oesrerschelde rhe input Q£ fresh water
is so small, that the area is better characterized as a sea arm than as
an estuary. Salinity is high and constant; turbidity, concearrations of
nutrieets and pollutants are low. Before the constructioo of the