Hydro-ecological relations in the Delta Waters

estimated primary production of 500 g C mdZy-l in shallow are-. The
contribution to the annual carbon budget of the Veerse Meer is roughly
-E -1
120 g C m y , which is 27X of the lagow' budget. The higb nitrogen
load not only leads to a relatively high production of phytoplanktou,
but also to intensive and undesirable mass growth of =in
areas.
shallow
Figure 7 reveals the inareae and decrease in biomass, eapressed as
perrentage wvezage, in a permaaent saaple plot In the Grevelingeu and
in the Vwse Fleet!. In the Grevelingemeer the annual cycle of cbaagerr
in biomass of seagrass is not disturbed by macro-algae. which have only
a low presence. In the Veezse Meer the seagraes plot becomes cmpletely
damindted by quickly growing-, suppressing the growth of zostera.
Table 3 shows that the eutrophicated Veerse Meer has the highest tmtal
-2 -1
primary production (roughly 4-50 g C m y ) and that the nutrient
limited Oosterschelde estuary has the lowest values (rdu@ly
-P -1
240gCrn y 1.
For Ereshwater ecosystems a tentative model has beau developed,
descrihlng the relation berween the relative domtuanca of primary
producers wmected to the availability of nutrients. and the
successive phase$ in the process of %acreasin% eutrophicatton
(Phillips. et al. 1978; Van Vierssen, et al. 1985; De Nfe. 1987: Fig.
8, upper panel). The model for esruarine and lagoonal situations Rig.
8, loaez panel) is adapted, based on data from the Qrevelinpn and
Veerse &er. The model is odly applicable to stagnant brackish lagoons
and extremely sheltered parts of tidal estuaries. In "healthy" saline
waters, waterplants - such as seagrasses - dominate. Nitrogen load and
concentrations are lm and the relative importance of phytoplanktm in
the shallow seagrassbeds is iusigniEicant; the Grevelisgeumeer is an
example of phase I. Zn brack3sh waters where eutropbiearim increases,
revealed by higher nitrogen loads and concentrations and lower,
instable salinities, waterpLants am outcompeted by macto-algae.
Epiphyte gowth gn seagrass-
increa~es considerably together with the
relative dsmtnanee of pbytoplankfou. The resilience of the aquatic
cmumnitied decreases, which makes the system less constant in time end