Hydro-ecological relations in the Delta Waters

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EUTROE%ICATION OF Tfts WATERS OF TEE DELTA J.E.W. de Hoog and B.P.C. Steenkatnp ABSTRACT A number of stagnant and serai-stagnant water systems came into being a6 a result of the recently completed hydraulic ehgiueeritlg works in the Delta area of the Aerhe~litnds. Eutrophication can occur in these waters as a result of the input of nutrient-rich river water. l%ia paper describes the eutrophication situation of bwo water systems in the Delta area2 the Hollands Diep/ Heringvliet and the Volkerak-Zoom lake system. In the E~llaods ~ie~iliaringvliet the residence time of the water depends on the discharge of the sivex Rhine. In years of low discharge the restdance time is relatively long and, especially in the western part of the Haringvlier, a large biomass o$ algae can appear as a result of eutrophication. In pars of moderate OT higher discharpes sf the riv$r mine this water system behave8 like a slowly flovlng river with relatively short residehce times ad a s41all hiamaes of algae, The Volkerak-Zoom l& system came into being in 1981 and after a period of desalinization changed from a saline tidal area into a freshwater stagnant reservoir. The most important input of rrater is from the XolLands Diep and the river Dintel. Computer modelling indicates that the lake will develop into an eutrophlc lake anleas adequate measures
are taken. The first year after the desalinikation proved mmre favourable thm predicted (the himas8 of algae was relatively small and transparency was ghod), but the input of nutrients meds to he limited still further in order to arrive at an enduring Iavouzable water quality, In addition, "active biological management" should be considered, i,e. the applicatimn of biological management raeasnres to obtain a healthy water system wfth clear water, an abundance of aquatic plant@ and a stock of predatory fishes that wrll keep the whitefish within bounds and hence allow sufficiefit eooplankton to remain to graze on the algae. Eutrophication is the enriehmerrc of a water system r*ith plant nutrients (also simply called nutrients), of which nitrogen and phosphate are the mast important. Eutrophication is partly a natural pzoeass: erosiofi and leaching wash nutrients inta zivers, wkich transport them to the lower reaches. Therefore, delta areas are natur.%lly wtrophic, and the Dutch Delta area is a good example. In the last 100 years humanity has greatly exacerbated the natural process of eutrophication. The insrallatien of drains ad sewers, the use of detergents and fertilizers and the increasing intensfficstion of livestock fanning have led t0 the amounta of nutrients in the rivers being increased many times over. Tn sttagnant water the enrichraent with planr nutrients can lead to m increase in the growth of algae, which can reault in high 4ensities of algae. Large numbezs of algae 14 the water results in a lev transparency; when the algae dh aeaerobim can occur and thie In turn can lead to fish mortality and a bad emell. Furthermore, toxic species of algae can occur (blue-green algae). Some species £am floating mts. Sa~tions 2 aad 9 of this paper describe the eutrophication situation of two Serni-stagriant water systems in the Delta area: the nollands Dlepj Haringvliet ad the Vohrak-Zwm lake system. The wtrophtcation state
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 and 26: Figsrlre 7 Changes in the cadrnrum
Page 27 and 28: prevention measures are desirable h
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: ShLOUONS, W. and BYSINK, W.D., 1981
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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