Hydro-ecological relations in the Delta Waters

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(M~tilus edulis) in salt water, Cerastoderma glaacum and Mya arenaria in brackish water and the Zebra Mussel (Dreissena polymorpha). Pisidiidae and Anodontidae in fresh water, feed mainly on phytoplankton. Under normal oonditiona filterfeeders dominate the hiomass. Uoarever, they are often the first species to decline or disappear under poilution stress. In salt and bracWsh water several polychaetes (e.g. the Lugworm Arenicola mariua) , molluscs (e.g. balthica) and crustaceans feed on detritus, others are scavengers or predators (e.g. the Shorecrab C a r d s maenasS. Especially in the saline lakes the epibenthos must be very i!qpartant although available data are scarce. It consists of shrimps (Grangon sp. and Mysidaceae) and nany other species of Crustacea (Isopoda and Amphipoda) . In fresh water Polychaeta are replaced by Oligochaeta and Chirononddae. All these organisms form the prey of the different species Of bentbivores such ss waders and d%ving ducks. Shrimps and mysids are also important pzey for gulls (e.g. Black-beaded Gull) and terns dnring the breeding season and for some species of grebes in winter. The diet of the Pochard, a diving duck, consists in the Delta mainly of the seeds of Eelgrass (Boudewijn and Mes, 1986) and this species is consequently included with the herbivores in our fuxther calculations. Benrhas and zooplankton also form the food source for many fish species, which in turn are eaten by the piscivores as Cornsrant, mergansers and grebes. This basic food web is quite smlar for the different haslns, although - mainly depending on the salinity - different species are fouad and depending on the hydrodynamical conditions different links of this food web are more imporrant. The various functional groups of birds described abuve (benthivores, piscivores, herbivores) are used in further analysis and called bird groups. Benthivores were divided into waders and diving dncks as these groups differ so markedly in the habitat they use (tidal flats versurr open water). Gulls are mainly omnivores and are also treated separately. Terns, typically piscivorous birds, are nor included in the analysis, as this species is not very well covered in the counts. In addition their feeding areas are not well knovn. Since they are rather
small bird$ extludiag them vill net si~cantly change the co~clusions. DISTRIBUTION OF DIFFERENT BIRD GROUPS based on numbers IN THE DELTA Figure 6 Oecurrewe of different bird groups in the different basins. 7er each group the percentage tm the total number of birds is given. (For abbreviations see FLgwre I; the bird grbups are defined h the text: and in the Appendix) To gaia insight into the distribution of waterbirds over the different basins the proportim of each bird group on the total number per basin is given in Flpre 6. The Voordelta is clearly different from the other sites with a very high proportion of gulls, few waders and quite many diving ducks. The three estuaries, Krammer-Volkerak, Dosterschelde and Westerschelde, are very similar in having a very high proportion of waders and - to a lesser extent - herbivores and gulls. The relatim importance of the different bird groups in the Lakes is quite similar aod characterized by a dominance of herbivores. Corepared to the estuarine situation the importance of waders in the lakes decreased
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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
Page 68 and 69:
model calculations reveal that a ni
Page 70 and 71:
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
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: . DISTRIBUXIOBI OF WATEJBIRoS OVER
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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