Hydro-ecological relations in the Delta Waters

In 1976 the determination of chlozopkyl levels was still in its
infancy, put the few daca available indlcate that in that exceptionally
dry year there vas an increase in the biomass of algae towards the
Baringvliet slnices. The picture ww very diffezent in 1987: in that
year the was very little dffference in the amounts of algae along the
weire trajert from Lobith to the Haringvliet sluices.
This disparity can be oXplained by studying tXe river discharges of the
various years,
In L976 the mean smer Rhke disaharge was well below 1700 mars; in
that year the Haringvliet sluices were slrarcely used the whole emer.
In 198% the mean s u s Rhine discharge was approximately 2200 m','$;
therefete in that year the sluices were regularly in use. In the smer
of 1987 the Ehine discharge was well above the mean discharge. and
therefore the sluices were used almost daily to discharge the E-l~er
water into the sea (Table 1).
Table 1 Mean smer chlorophyl level and Rhine discharpe in 1976,
1989 wd 1987.
chlorephpl
(ms/m3)
Ehine discharge
(g/.)
Computer Sirmtl&EionE dbne at Delft Hydraulics have also shm that the
behaviour of algae in these watetri greatly depends on the vater
movement is this area. The eutrophicatian in 1976 and 1982 was
sfolulated with the DBLWbQ-BLOUX model. &B input the made1 requires data
@n the water mowameat in Ehe Various river channels, the concentrations
df uzttrients and algae in CIre incoming river water, climatological
factors rlna properties of algae. As output the model supplies the algkl
hiomass far each location in the area am4 for each day of the year.