Hydro-ecological relations in the Delta Waters

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The mein diet of piscivores in the salbe waters consists of Cobiid fish (Pomatosehistus microps, P. minutums, P. loaanei). In the Grevelingen Meer the diet of Great Crested Grebe consisted for more then 60%: (by weight) of Gobiidae (Domrnbos, 19$4). Other important species were Herring (C1,u~eq harengus) and Shrimps (Grangmn crangon) . The Three-spinod Stifkleback (6asterosteus aculeatus) is very abundant in the Veerse Meer (Waardenburg and Meiler, 19881, but it is not known ta &€it esent they $re eaten by birds. As GmbFid fish fenus the majority of the diet and more PT less comparable data are available, the average winter density is even h Table 2 together with tha densities of pibcivofes. Clearly the highest densitieg of bath fish sad birds are found ib the Veerse Meer. In the Voordelta the nobiid densities ate varg varia%lo and prehably transparency. wMth is very low, end wave action prevent Birds from feeding here. In the tidal areas and the saline lakes a clear relation bstwesn ptscivore densities and Gobffd densities is found. In the froshwatar lake6 ratber high densities of piscivores are found. Perch (Perca fluviatilis), Boaeh (Rutilus ~tilus) and other Cyprinidae as well as Gasterosteidae ere inportant prey species in these lakes. Howevr;~, no density eqtimations are available. The bibmass of macrozoobenthos end the dessities of waders and diving ducks ere given in Table 3. Waders occur -My on intertidal areas here they feed on *any dzffetent species @f izverteh~afes. Same waders are very speciUred, for instance Cystercatchers which feed mditrly 6zl Mussels and Cackles; others suCh as Dunlin feed on a verierp of polychaete worms (Rerefs sp.; Scoloplos armfger =Cc.) and small crustaceans (e.g. Corophiua sp.) whereas Bar-tailed Godwits feed on both worms, crustaceans and molluscs. Sometimes the diet ohansea with the seasons. In autumn the diet of Curlew oonaists mainly of the Sharecrab wbereas in winter, when the crabs move to deeper water, Curlews feed l~iiinly on large worms (Lugwonus and Nereis sp.). In the tidal basins an obvious relation between the densities of waders and the available biomass extsts. A very high bkmass and density is fomd fn the Ooeteyschelde, much lower valnes in the Westerschelde and Kramer-Volkerak. The densities of waders in the other basins are much lmer and as they arzt i?ee-g these in a veriety of habitats, the diet
Table 3 Biomass of macroroobenthos and densities of waders and diving ducks in the different hasins af the Delta =ea. The average autumn biomass (g ash free dry weight/m2) of the whole basin and of the intertidal area and the density Q£ waders and duoks (birds1100 ha) are given. (Source of macrozoobenthos data: (1) Craeymeersch (pers. cam.) (2) Coosen and Van den Dool, 1983 (3) Coosen and Smaal, 1985 (41 Meire and Develter, 1988 (5) Lamheck, et al, 1985, 1986, 1987. (6) Seys and Meire, 1988 (7) Fortuin. 1985.) For abbreviations see Table 2. Basin biomass hiamass source waders diving overall intertidal ducks is not lmam and hence it is not possible to calculate the available food supply. Diving ducks like Goldeneyes and Tufted Ducks feed mainly on molluscs (Zebra Mussels, Mussels, Cockles etc.) as well as on different species of wow and crustaceans. A relation between macrobenthic biomass and the density of diving ducks is not clear at all. The highest densities of diving ducks are found in the Veerse Meet, although the biomaes is lower than in other areas. Additionally in the freshwater lakes high densities of diving ducks are found although the benthos biamass is very Low. On the other hand in both the Qosterschelde and the Krammer-Volkerak a larpe benthos biomaas is present but remsrkably low densities of diving ducks are found. Clearly other factors must influence the distrihutfon of these birds. This will be discussed later.
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Netherlands organkation fw applied
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TNO Commlitee on Hydrological Resea
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2 RIVER WATER AM) THE QPALITH OF TB
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B.J.M. Baptist BIJkswaterstaat. Tid
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This approach will put to use what
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Estuaries that have not been influe
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2 CHIWGES XN TEE DELTA The Delta ar
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area decltned cnnside~ably, leadins
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Plan, then it is apparent tbt the s
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Tiddl flats df the Eastem Seheldt v
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tracefore possible to convert the a
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Figsrlre 7 Changes in the cadrnrum
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prevention measures are desirable h
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elationships between different spec
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Bio-essay Weriments with polluted s
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considerable thought to drawing up
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ShLOUONS, W. and BYSINK, W.D., 1981
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are taken. The first year after the
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The Hollands DiepJnaringpllet is pa
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In 1976 the determination of chlozo
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, 0.66 m 0,s - 0.02 1989 I 0.86 - 0
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Table 3 Eutrophication of the Volke
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Laks Volkarek ---- Lake Zoom 0.40 0
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4 WAGBEET MEdSIIRaS TO PEEVBT OR LT
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Table 5 gives estimtes of the phosp
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In principle, two states of equilib
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Zooplankton (Alma affinis) Pike (Es
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EUTROPHICATION OF ESTUAAIES AND BRA
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The average discharge of Xhine and
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and only l-2% cows frm the aive Sch
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highest trophic potential: nutrient
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period 1980-19$3 in an increase of
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model calculations reveal that a ni
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Table 3 PreUmInary carbon budget of
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Water life of Lake Grevelingen
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macrophytes livkg on or rooting in
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less predictable for water managers
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ILWNEWIJK, A.. KEIP, C., 1988. De v
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XBE CHANGING TmAL LAMXiCAPE I N TEE
Page 82 and 83: The storm surke of L&Z1 A.D., knorm
Page 84 and 85: osi* rn@8IOIP m .SL 4 Has F~~ULB 3
Page 86 and 87: During the 19th century man starts
Page 88 and 89: mudflats have retreated some 100-20
Page 90 and 91: aq811~33a.e~ pue 3pTatlJS uxaJsafi
Page 92 and 93: Erosion by waves of sandy shoals (c
Page 94 and 95: Lt has been estimated that the sedi
Page 96 and 97: Implementafion of the Delta Project
Page 98 and 99: ECOLOGICAL DEVELOWdENT OF SALT MAKS
Page 100 and 101: fn tidal water systems sedimentatio
Page 102 and 103: hierarchical position. Tn the egtua
Page 104 and 105: Of course. tke environmental change
Page 106 and 107: wind erasson, desaliuation, aeratio
Page 108 and 109: Fonner tirtal flats with saltmarsh
Page 110 and 111: Grevelingen. Lake Veere and Krammer
Page 112 and 113: As mentioned above aa important que
Page 114 and 115: A seaond important perspective for
Page 116: BEEEXNX, W.D. and 80ZBf&. J. L9M. T
Page 119 and 120: are determining the dfstrlbution af
Page 121 and 122: this volume or in Duutsaa, et aL, 1
Page 123 and 124: artificial waterflow was created af
Page 125 and 126: of waterbirds occur regulsrly. The
Page 127 and 128: . DISTRIBUXIOBI OF WATEJBIRoS OVER
Page 129 and 130: small bird$ extludiag them vill net
Page 131: In order to lsok for relatiouehips
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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