Hydro-ecological relations in the Delta Waters

period 1980-19$3 in an increase of the anaerobic sed-t suzface area
of 4 ta 258 of she entire bottom awfkce (Stronlrhorst. et al. 1985).
Qbvioualy, the Veerse Meer is vulnerable to eutreghicatian, owing to
the long resid&&e the of water msses, the low extinetian coefficient
and the ;Umost permanent stratification.
The Oastesschelde estuary has a very low N-lead re6nlting in low
chlorophyl concentratisne (Table 2).
Wing to the execwtina af the
Deltaplan (Pig. 1) the Oostarnehelde estuary has mainly been depriVed
recently from its Bhinewater loading (Table 1). Model calculations
revealed that a reduction of 50% of the nitrosen bed of the river
W e
would only lead to a rsduetian of less than 6% for nitrogen
eoneentratlons in the 0oster.jkbelde estuary (Smobs-swdel; X. Scholten,
peraerial co~u~ication). The Uoster~ohelde estuary is rnainly ir;fluenced
by tearhe foastalwffter, containing low conewtrations of total
nrtrogen (less than 0.5 slg N 1-l; Srockolano, et al. 1988).
Contkaq to the Veerse Meer lag~an. the Creveliagen lagoon has an
-2 -1
e%treaely Low N-load (4 g N m y ; Table 2). The CaeWA~mdel (De
Vries, et al. 19BEI) revealed that Khe prodtlrcim of phytop.lanktan La
the Gzevelingen is liodted by nitrogerl availability and not by light
availability. The hl
: P ratio of tae dlsselved nufkiems in cke
watercolm of the GrwsMngenmeer durins winter is 2-4,
poirtcing into
the direction of a large surplus af phosphate, notwithstanding Che
dominance of nitrogen in the discharge utatet, loading the lagoon
Eff : P = 22 : I f. Model calculations showed s Mgh tunrover of ni~rog.~u,
in the watercolumn. The chain of processes: nutrient uptake by
phpoplanktaa - forslation d organic matter in algal cells -
mherallzation of dead algae - regeneratbn of nutrients etc.. occurs 8
tWs a year. &out
90X of the anme1 prisary pr&uction of
phytoplanktoa occurs on the baeis of resewrated nutrients, especialLy
NB4 CDe Vtim, et al. lS88).