Hydro-ecological relations in the Delta Waters
Hydro-ecological relations in the Delta Waters Hydro-ecological relations in the Delta Waters
4.2 Active biological management If it is considered desirable to have clear water in the next ten years too. then "active biological management" could be emplop3. Furthermore, experience elsewhere (e.g. in the Veluwe lakes) and computer modemg btdleate tbat Sr is difficult far a lake that is already in "turbid equilibrium" to be made clear again. / transparency algae +++i-t+++t+U /--L +++*M + asuatiq plants ++-+tit+ \/ preatory fish +++CH*H+++++ nUttianfs '2w00000~ l *&a, wblteeirih ----- MOOOWOO~O aemal state si Vol%asak-%oon lake aystem autrophic rster o m mixed agsten +++c healtay water syseem - path of influence er flaw of mather HignEe 10 Schematic representation of ecosystem relatianahips in a autrophic water body Bigure 10 shows the most important relationships between the various components of a lake eeosysfem. Nutrients enhance the growth of algae; algae are eaten by zouplaakton; zooplankton are eatea. bp whitefish; +#kitefish are eaten by predatory fish; pre&cory flsh, particularly pike, requite aquatic plants fot shelter and for breeding, atld the occurrence of aqnatic plants depends on the transparencg of the water axid thus also an the absence of algae.
In principle, two states of equilibrium are possible in such a system. One is an eutrophic, relatively turbid system dominated by marry nutrients, many e a e and m y whitefish; this is indicated by - in Pisure 10. The other possibility is a healthy functtoning system with transparent water, many aquatic plants, a predatory fish populaticn that keeps the whitefish population in check, and sufficient aooplanktan to be able to grase the algae effectively. In Figure L0 this is indicated by +Wt. In 1988, contrary to all ptedietions, the Volkerak-Zmom laka system contained elemnts from both passible equilibrium situatians - many nuttients, transparent water and m y zooplankton: this is indicated by ooa0 in Figure 10. In 1988 aquatic plants started to develop, but not sufficiently ta offer shelter and a breeding enviranmeot for predatory fish. The few data available on stocks of fish suggest that the bream, a whitefish that often causes problems in other eutxaphic waters, is not present here in large mumhers. Predatory fish, especklly pike-perch. are present in the system. The most obvitlus way of acaidy intervening in the biology 05 the system is to stiPtulate the develspmnf of aquatic plants as much as possible. Few propagules of freshwater aquatic plants vtll be present in ttte system, and therefore it is advisable to introduce material from the desired species into the system on a large scale. It is also important to ensure the presence of sheltered shallows, because in princfple here it is that aquatic plants can develop the hest on q large seal&. Proper management of fish stooks requires agreement between the water authority and the persona with fishing rights. Quantitative wnitori~g is necessary to be able to properly anticipate developments towards an excess of bream.
- 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 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: Table 5 gives estimtes of the phosp
- 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
In pr<strong>in</strong>ciple, two states of equilibrium are possible <strong>in</strong> such a system.<br />
One is an eutrophic, relatively turbid system dom<strong>in</strong>ated by marry<br />
nutrients, many e a e and m y whitefish; this is <strong>in</strong>dicated by - <strong>in</strong><br />
Pisure 10. The o<strong>the</strong>r possibility is a healthy functton<strong>in</strong>g system with<br />
transparent water, many aquatic plants, a predatory fish populaticn<br />
that keeps <strong>the</strong> whitefish population <strong>in</strong> check, and sufficient<br />
aooplanktan to be able to grase <strong>the</strong> algae effectively. In Figure L0<br />
this is <strong>in</strong>dicated by +Wt.<br />
In 1988, contrary to all ptedietions, <strong>the</strong> Volkerak-Zmom laka system<br />
conta<strong>in</strong>ed elemnts from both passible equilibrium situatians - many<br />
nuttients, transparent water and m y zooplankton: this is <strong>in</strong>dicated by<br />
ooa0 <strong>in</strong> Figure 10.<br />
In 1988 aquatic plants started to develop, but not sufficiently ta<br />
offer shelter and a breed<strong>in</strong>g enviranmeot for predatory fish. The few<br />
data available on stocks of fish suggest that <strong>the</strong> bream, a whitefish<br />
that often causes problems <strong>in</strong> o<strong>the</strong>r eutxaphic waters, is not present<br />
here <strong>in</strong> large mumhers. Predatory fish, especklly pike-perch. are<br />
present <strong>in</strong> <strong>the</strong> system.<br />
The most obvitlus way of acaidy <strong>in</strong>terven<strong>in</strong>g <strong>in</strong> <strong>the</strong> biology 05 <strong>the</strong><br />
system is to stiPtulate <strong>the</strong> develspmnf of aquatic plants as much as<br />
possible. Few propagules of freshwater aquatic plants vtll be present<br />
<strong>in</strong> ttte system, and <strong>the</strong>refore it is advisable to <strong>in</strong>troduce material from<br />
<strong>the</strong> desired species <strong>in</strong>to <strong>the</strong> system on a large scale. It is also<br />
important to ensure <strong>the</strong> presence of sheltered shallows, because <strong>in</strong><br />
pr<strong>in</strong>cfple here it is that aquatic plants can develop <strong>the</strong> hest on q<br />
large seal&.<br />
Proper management of fish stooks requires agreement between <strong>the</strong> water<br />
authority and <strong>the</strong> persona with fish<strong>in</strong>g rights. Quantitative wnitori~g<br />
is necessary to be able to properly anticipate developments towards an<br />
excess of bream.
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