Hydro-ecological relations in the Delta Waters

highest trophic potential: nutrient concentration values never approach
zero during spring a~d sumer and reach hi&h levels Buring wtnter
(8 mg 1-l N; 4 m$ l-l P and 9 nrg 1-l Si). Compmd t9 the nutrient
coneentratious in the river Rbine (Fig. 2). F-concentrations are wo
tiares lover and N-emcenttations are ten times 1-
water badies (Fig. 5).
exeept far the Weaterschelde,
id the saline
Veerse Meer -N
Figure 5
Range in nutrient concentrations in esfuaries and brackish
lagoons in the South-West Netherlands.
See legend Table 1 for souzces.
The question arises which factox acts as the limiting constituent for
the productivitr of algae in the saline Delta Waters. In the turbid
Westerschelde it seems obvious that the availability of light is
limiting phytoplankton dynamics. In brackish coastal waters phospate
may he a potentially limiting factor (Veldhnis, 1987). It is generally
assumed that nitrogen is the limiting factor for phytoplankton
development in the Oosterschelde and Grevelingen and occasionally also
in the Veerse Meer. Knowledge about phytaplankt~n and wcrophyte
kinetics in the South-West Netherlands, however, is scanty. Especially
in polluted estuariee like the Westerschelde other factors than
nutrients and lighc availability may he responsible fox the limitation
of algal photosynthesis. It is now becoming increasingly obvious that
antagonistic effects beween metals on phytoplankton exist, whereby an
organism may tolerate high concentrations of a given metal in the