Hydro-ecological relations in the Delta Waters

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As birds are mainly top predators, they accumulate quite a lot of toxic substances. The dramatic effects of chlorinated hydrocarbons, insecticides and chlorinated biphenyls on many piscivores in general and especially on the Sandwich Terns in the sixties, decimating their pop~lations are well known (Koeman and Van Eenderen, 19721. The effects of accwwlation of pollutants ere, hmever, not always so obvious, neverthelens they wy severely affect populations. Pew data on conoentrations of pollutanrs in birds in the Delta area are avaFLahlc. However, experiments with Tufted Ducks clearly deman$trafed that when fed With Zebra Mussels from the Raringvliet their reproductive oatput was v eq much depressed IMarquenie, et al. 1986; Seholten and Poekema, 1988). Clearly pollution is a major factor affecting birds in the Delta area and, as its effects are vey diverse and by now not very well onderstood, much mere attention should he paid to this problem in the Eutnre. Babitat loss is ~f course a very impartant factor influencing birds. The effects are obvious. In the remaining areas bird densities increase, causing a higher predation pressure and hence a smaller food supply. This tpgether with an inereased level of social iateractions between individuals can reduce quite aubsfantiallp the food intake lead* td death. detailed revietv af the effecrs of habitat loss bn wader populatione is given by Goss-Custacd, 1985. It shauld be nated that hahicat lams is not only cased by physical removal of an anea but also by deterioration of the food supplp e.g. due to changing environmental condition#. In the Westerschelde the increased dredging activities cause the intertidal flats to become more sandy shee in the larger channels higher current speeds occor, influencing the sedimentation patterns. The benthic fauna and the numbers of waders are much smaller on send- than on mudflats. This is especially in the Wesrerschelde a severe threat.
m's activiries do not always have to affect ecoaystw in general or bir& in particulex in a negative way. Indeed m y management measure4 ean be taken to improve the arituation, measures which often are rather cheap but very effective. Oe the Hooge Platen, a large intertidal flat in the Westerschelde, a small part 19 flooded wly at extreme bigb tides. The constructidn of a small dike hy meane of sadbags made the site very attractfoe for Little Terns. The population increased from 60 in 1979 to 170 in 1985 (Pig. 10). a threefeld increase. compared rrlth a NUMBERS OF BREEDING PAIRS OF LITTLE TERN ON THE HOOGE PLATEN 1979-19BB Figare 10 Eyelutian of tbe number of breeding Little Terns w the "Woge Plaacen" i~ the Wesrerschelde (data RQQ R. Beijersbergen, peasonal eonrmunication~ 1.3-fold increase in the whale Delta during the same time (Mein&ger, 1966). On many of the artifiaial islands in the Oostersdlelde, f~rmerly used during the construction of dams, sluices etc., there are
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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
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The storm surke of L&Z1 A.D., knorm
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osi* rn@8IOIP m .SL 4 Has F~~ULB 3
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During the 19th century man starts
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mudflats have retreated some 100-20
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aq811~33a.e~ pue 3pTatlJS uxaJsafi
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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: Bewick's Swans (Cygnus columbariusl
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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