Hydro-ecological relations in the Delta Waters

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It is possihle that in the future a more liberal flushing policy might be adopted $n connection with the improved water ~ualitg in the rivers Rhine and Lleuse. Hawever, it should be borne in mind that not all the pollution parmeters have been reduced to the same ertent as cadmium. In the Western Scheldt the situation is different from that described abwe since this rwion haa not been faflueneed by the closure operations. Boww@r, significant amaunts of sed-t have been deposited over the last deaades in the Land of Saeftinghe area, Which conaists of extensive salt marshes and mudflats. This has been caused by the deepening of the bars in the eaetern part of the estuarp for shipping purposes, which have increased the t%dal difference and also the turbidity. Conruequeutly. a layer between 0.2 and 0.4 m has recentbeen deposited in thLe area. Polluted silt from the river Scheldt is sect* here together with uncontaminated sea-bane sediment, in the ratio 608 liver silt to 44% sea silt. & a result of the comfruction of the Delta Works, as described in the previous chaptezs, the central seetiou of the Delta has been cut off froa tbe ingluence of the major rivers to some extant. Hewever, this does not necessarily guarantee the quality of the estllary and lake beds, which 3s affected bot& by past influences as by local 8ources of pollution. It is inpurrant to take this inea account view of the radical changes which tbe hgdranlic and aiorphblogical confi@uraeian of the regLon had mdcrgone. For instance, rhe cmpartentslization of the takes Grevelingen. Beere and Vblkerak-Zoom bad cbnsidetahly ibcrea-sed the residence tima of water. The construct'ion of the storm-surge barrier in the Eastern Soheldt haa also led to a oonsiderable reduction in the hoxizontal tide, as a result of which residence the had ineressed and the Eastern Sch%lde has becorn a pure sedimentation area. In shsrt, the centrl section of the Delta has becoma much more vulnerable to local pollution. Local pollution mafnly emmates from diffuae sources; the main ones are acrivrties in the smaU hsrbonfs in this region and the discharge of water frm the polders. It has been obsemred that the beds of all of these harbours are moderately to aeverelp polluted. Clean-up and
prevention measures are desirable here to prevent the diffusion of pollution to adjacent waters. 5 EFFECTS ON THE ENVIRONMENT Relatively little is knm about rhe impact polluted beds have on aquatic ecosystems, partly because these areas are not directly obsesvable. Future research strateges will therefore be mainly concerned vith addressing these shorreomings. There are, however, various indications that pollution m y be a hazard to public health md may influence the functioning of aquatic ecosystems. The presence of heavy metals ad organic micropollutants in benthic organisms is clearlybigher in polluted areas rhan is less wntaminated areas. This has been verified for various organisms such as Dreissena palymol-pha. Tubifex spec., miromid larvae and also zooplankton (Urk, 1987). There are, of course, specific differences between individual species with regard to the type and mwunt of heavy metals found. In molluscs, for example, contamination levels are Ngher in species that live ia the top layer of sediment than surface dwellers. Kelatively low levels of p@llution are found in the eastern part of the Xarin$vliet basin (Hollands Diep), whereas higher levels can be detected in the western part of the Baringvliet. This is a coneequence of the sedimentation process, which has influenced the quality ef river sediments in the areas, as outlined in the previous section. These gradients are also reflected in the concentration of contaminants found in specific organisms. Xigure 8 shows how the cadmium content 3s the gills of Anadonta anatina varies at different locations. The levels in the western part of the basin (Haringvliet) are two to three t h e higher than those found in the eastern part (ILollands Diep) . Simular problems have been encountered with orgsnie micropollutante. For instance, from 1977 to 1985, PCB levels in eels from the different surface waters in the Wetherlands were monitored bg the State Institute for Fishery Research CRIVO). At the end of the seventies PCB levels in eels from the BaringvlieL basin were extremely bigh, prohahle as a result of local discharges, some of them illegal. Since tbis time, the
Page 1 and 2: Netherlands organkation fw applied
Page 4 and 5: TNO Commlitee on Hydrological Resea
Page 6 and 7: 2 RIVER WATER AM) THE QPALITH OF TB
Page 8: B.J.M. Baptist BIJkswaterstaat. Tid
Page 11 and 12: This approach will put to use what
Page 13 and 14: Estuaries that have not been influe
Page 15 and 16: 2 CHIWGES XN TEE DELTA The Delta ar
Page 17 and 18: area decltned cnnside~ably, leadins
Page 19 and 20: Plan, then it is apparent tbt the s
Page 21 and 22: Tiddl flats df the Eastem Seheldt v
Page 23 and 24: tracefore possible to convert the a
Page 25: Figsrlre 7 Changes in the cadrnrum
Page 29 and 30: elationships between different spec
Page 31 and 32: Bio-essay Weriments with polluted s
Page 33 and 34: considerable thought to drawing up
Page 35 and 36: ShLOUONS, W. and BYSINK, W.D., 1981
Page 37 and 38: are taken. The first year after the
Page 39 and 40: The Hollands DiepJnaringpllet is pa
Page 41 and 42: In 1976 the determination of chlozo
Page 43 and 44: , 0.66 m 0,s - 0.02 1989 I 0.86 - 0
Page 45 and 46: Table 3 Eutrophication of the Volke
Page 47 and 48: Laks Volkarek ---- Lake Zoom 0.40 0
Page 49 and 50: 4 WAGBEET MEdSIIRaS TO PEEVBT OR LT
Page 51 and 52: Table 5 gives estimtes of the phosp
Page 53 and 54: In principle, two states of equilib
Page 55 and 56: Zooplankton (Alma affinis) Pike (Es
Page 58 and 59: EUTROPHICATION OF ESTUAAIES AND BRA
Page 60 and 61: The average discharge of Xhine and
Page 62 and 63: and only l-2% cows frm the aive Sch
Page 64 and 65: highest trophic potential: nutrient
Page 66 and 67: period 1980-19$3 in an increase of
Page 68 and 69: model calculations reveal that a ni
Page 70 and 71: Table 3 PreUmInary carbon budget of
Page 72 and 73: Water life of Lake Grevelingen
Page 74 and 75: macrophytes livkg on or rooting in
Page 76 and 77:
less predictable for water managers
Page 78 and 79:
ILWNEWIJK, A.. KEIP, C., 1988. De v
Page 80 and 81:
XBE CHANGING TmAL LAMXiCAPE I N TEE
Page 82 and 83:
The storm surke of L&Z1 A.D., knorm
Page 84 and 85:
osi* rn@8IOIP m .SL 4 Has F~~ULB 3
Page 86 and 87:
During the 19th century man starts
Page 88 and 89:
mudflats have retreated some 100-20
Page 90 and 91:
aq811~33a.e~ pue 3pTatlJS uxaJsafi
Page 92 and 93:
Erosion by waves of sandy shoals (c
Page 94 and 95:
Lt has been estimated that the sedi
Page 96 and 97:
Implementafion of the Delta Project
Page 98 and 99:
ECOLOGICAL DEVELOWdENT OF SALT MAKS
Page 100 and 101:
fn tidal water systems sedimentatio
Page 102 and 103:
hierarchical position. Tn the egtua
Page 104 and 105:
Of course. tke environmental change
Page 106 and 107:
wind erasson, desaliuation, aeratio
Page 108 and 109:
Fonner tirtal flats with saltmarsh
Page 110 and 111:
Grevelingen. Lake Veere and Krammer
Page 112 and 113:
As mentioned above aa important que
Page 114 and 115:
A seaond important perspective for
Page 116:
BEEEXNX, W.D. and 80ZBf&. J. L9M. T
Page 119 and 120:
are determining the dfstrlbution af
Page 121 and 122:
this volume or in Duutsaa, et aL, 1
Page 123 and 124:
artificial waterflow was created af
Page 125 and 126:
of waterbirds occur regulsrly. The
Page 127 and 128:
. DISTRIBUXIOBI OF WATEJBIRoS OVER
Page 129 and 130:
small bird$ extludiag them vill net
Page 131 and 132:
In order to lsok for relatiouehips
Page 133 and 134:
Table 3 Biomass of macroroobenthos
Page 135 and 136:
freshwater basins. Clearly the pres
Page 137 and 138:
scmthem bottueary o-f the winter di
Page 139 and 140:
OCLURRENCE AND DIET QF B ~T .tUQ 80
Page 141 and 142:
5.2 H- factors Next to all fartors
Page 143 and 144:
Bewick's Swans (Cygnus columbariusl
Page 145 and 146:
m's activiries do not always have t
Page 147 and 148:
measure affecting food supply or av
Page 149 and 150:
DOQiWT$QS, G. 4 TWISK, F., 1987. De
Page 151 and 152:
MEININGEB, P.L. and HAPEREX, A.M.M.
Page 153 and 154:
PISCIVORES Litfle Grebe Great Crest
Page 156 and 157:
IPYBRO-EGOLOOIOAL BELATIONB ZN THE
Page 158 and 159:
apart from upstream purification; -
Page 160 and 161:
Storm surge barrier Eastern Scheldt
Page 162 and 163:
- In addition to existing managemen
Page 164 and 165:
Nature is pliable. Belattvely young
Page 166 and 167:
Ro. 1. No. 2. SQ. 3. Investigations
Page 168 and 169:
25. The relation between water quan
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Hydro-ecological relations in the Delta Waters

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