{"refrec":{"BRefID":603,"RR":"<b>van der Veer, H.W.; Beukema, J.J.; Cad\u00e9e, G.C.; Hegeman, J.; Mom, B.; Van Raaphorst, W.; Witte, J. IJ.<\/b> (1995). Effecten van antropogene activiteiten op de produktiviteit van het ecosysteem in de westelijke Waddenzee. <i>BEON Rapport = BEON-report<\/i>, 95(9). RIKZ: Den Haag. 56 pp.","BEntID":603,"PublicFlag":1,"CheckedFlag":0,"wosflag":0,"vabbflag":0,"RefStringPartII":". <i>BEON Rapport = BEON-report<\/i>, 95(9). RIKZ: Den Haag.  56 pp.","DocTypID":13,"DocType":"Reports","MarineFlag":1,"FreshFlag":0,"BrackishFlag":0,"TerrestrialFlag":0,"Authorstring":"van der Veer, H.W.; Beukema, J.J.; Cad\u00e9e, G.C.; Hegeman, J.; Mom, B.; Van Raaphorst, W.; Witte, J. IJ.","OrigTitleTranslFlag":1,"Authorstringtrunc":"van der Veer, H.W. <i>et al.<\/i>","Englishabstract":"The Wadden Sea plays an important role as a nursery area for fish and crustacean species and as a resting and refuelling area for migrant birds. During the last decades the area has become more and more influenced by anthropogenic activities, such as eutrophication and commercial fisheries. In this report a first attempt is made to study the impact of eutrophication and commercial fisheries on the productivity of the western Wadden Sea. The area of study is the western Dutch part of the Wadden Sea, an area under the influence of fresh water run-offs from the mainland and of intense water exchange with the adjacent coastal zone of the North Sea. In the first contribution, the trends in nutrient loadings of the western Wadden Sea from 1960- 1992 are reviewed. Annual nutrient loads of total-P and total-N in the main river Rhine at the Dutch-German border have decreased after a period of increasing eutrophication up to the late 1970s and early 1980s to values comparable to those in the 19605 and early 19705 again. Part I y due to inputs in the Dutch part of the drainage basin of the Rhine, total nutrient loads from the river Rhine to the coastal zone of the North Sea decreased substantially less during the last decade. The recent decrease in nutrient loads from the river Rhine, however, is not reflected in the total-N and total-P concentrations in the Dutch coastal waters close to the Wadden Sea. The main source of fresh water input in the area are the discharges of lake IJssel, which is fed by a branch of the river Rhine. The annual total-N and total-P loads in the discharges into the Wadden Sea follow a similar trend as in river Rhine, with a decrease during recent years to values as low as before the 19705. The concentrations of total-N and total-P in the western Dutch Wadden Sea followed the steep increase in loads from lake IJssel in the 19705, but showed a different trend hereafter. In contrast to the trends in the discharges of lake IJssel and in the concentrations in the adjacent coastal zone of the North Sea, concentrations of total-N and total-P in the western Wadden Sea dropped since the early 1980-ties and have stabilized at relatively low levels since then. At present concentrations are comparable to those in the 19605 and 19705. In a subsequent contribution the long-term trend in pelagic primary production near the Marsdiep inlet in the western part of the Wadden Sea is discussed and related to the observed trends in nutrient concentrations in the area. Annual primary production amounted to about 150-200 gC.m-2 in the 1960-ties and early 1970-ties. A doubling took place in the early 1980-ties and values have remained high since. Primary production in 1990 was relatively low, but the values for 1991 and 1992 were as high as those in the mid-1980s. A recent lowering is absent. The decline in especially total-P did not yet reduce the productivity in the area, although in the present situation P might have become a limiting factor tor primary production during a short period of the phytoplankton spring bloom. The two other contributions deal with the secundary production of the intertidal flats. Long-term observations of the macrozoobenthic biomass and productivity show biomass values of about 20 g ash-free dry weight (AFDW) per m<sup>2<\/sup> in the beginning of the 1970s, with an increase in the beginning of the 1980s to values of about 30-35 g AFDW per m<sup>2<\/sup>. No consistent decline was observed in recent years. Time-series over the period 1974-1993 on settlement and growth of juvenile flatfish (plaice and flounder) and shrimps showed no effect of eutrophication. Year-class strength of both groups appeared to be determined by other factors than the food conditions in the area. At present, there is no indication of a negative impact of decreasing nutrient concentrations in the area on biomass or productivity of the macrozoobenthos and the major juvenile epibenthic predators at the tidal flats. The other anthropogenic activity in the area, commercial fishing activities on the tidal flats for cockles and seed mussels, did have an impact on migrant birds. In the course of 1990 stocks of mussels declined to unprecedentedly low levels in the Dutch Wadden Sea. HardIy a wild mussel bed was left on the tidal flats as a consequence of three years (1988, 1989, 1990) with failing recruitment in combination with intensive fishing for seed mussels. During these three years recruitment of cockles also failed, whereas fishing was continued. Birds taking these bivalves as staple food, the oystercatcher and the eider, experienced food shortage. Significant numbers of eiders left the Dutch Wadden Sea area or died, whereas oystercatchers remained abundant throughout the winter in most of the Dutch Wadden Sea, but suffered from abnormally high mortality.","AbstractOtherLang":"De Waddenzee vormt een belangrijk opgroeigebied voor jonge vis en schaaldieren en als rust- en voedselgebied voor trekvogels. Gedurende de laatste decades is de Waddenzee meer en meer onder invloed gekomen van antropogene activiteiten, zoals eutrofi\u00ebring en commerci\u00eble visserij op vooral garnalen, kokkels en mosselen. In dit rapport wordt een eerste poging gedaan om de effecten van eutrofi\u00ebring en visserij in de Waddenzee op de produktiviteit van het gebied te kwantificeren. Deze studie richt zich op het westelijk deel van de Nederlandse Waddenzee. Het gebied staat onder invloed van zoetwater toevoer vanuit het IJsselmeer en van kustwater door middel van uitwisseling door de zeegaten. De eerste bijdrage beschrijft de ontwikkeling van de nuri\u00ebntbelasting van de Waddenzee vanaf de 60-er jaren tot heden. De jaarvrachten van totaal-N en totaal-P zijn in de Rijn bij de Nederlands- Duitse grens de laatste jaren afgenomen (na een periode van eutrofi\u00ebring, die eind 70-er en begin 80-er jaren zijn hoogtepunt bereikte) tot waarden vergelijkbaar met die in de 60-er en 70-er jaren. De afname van de vrachten in de Rijn wordt niet weerspiegeld in de concentraties aan nutri\u00ebnten in de kustzone van de Noordzee. De vrachten aan totaal-N en totaal-P in de lozingen van zoetwater vanuit het IJsselmeer in de Waddenzee, vertonen eenzelfde beeld als de patronen in de Rijn bij de Nederlands-Duitse grens, met een afname gedurende de laatste jaren tot vrachten die overeenkomen met de periode voor de 70-er jaren. De concentraties van totaal-N en totaal-P in de westelijke Waddenzee volgen de toename van de spui in de 70-er jaren. In tegenstelling tot de trend in de vrachten van de spui, laten de concentraties in de westelijke Waddenzee van zowel totaal-N als totaal-P echter al een afname zien voor het begin van de 80-er jaren, om daarna te stabilizeren op waarden die overeenkomen met concentraties in de 60-er en 70-er jaren. De tweede bijdrage behandelt de veranderingen in pelagische primaire produktie in de westelijke Waddenzee vanaf eind 60-er jaren tot op heden. De jaarlijkse pelagische primaire produktie bedroeg ongeveer 150-200 gC.m-2 in de 60-er en begin 70-er jaren. Een verdubbeling trad op in het begin van de 80-er jaren, en de produktie is tot op heden op dit hoge niveau gebleven. Hoewel in 1990 een relative lage produktie gemeten werd, zijn de waarden in 1991 en 1992 even hoog als in de 80-er jaren. Een verlaging gedurende de laatste jaren lijkt dus niet te zijn opgetreden. De afname van de concentratie van in het bijzonder totaal-P in de westelijke Waddenzee, heeft de produktiviteit van het gebied dus niet verlaagd, hoewel in de huidige situatie P een beperkende factor geworden lijkt te zijn gedurende een relatief korte periode tijdens de voorjaarsbloei. De twee andere bijdragen behandelen veranderingen in de secundaire produktiviteit op en in de getijdeplaten. Lange-termijn series van het macrozoobenthos in de bodem in het voorjaar laten een trend in biomassa en produktie zien vanaf de 70-er jaren tot op heden. In het begin van de 70-er jaren werden biomassa's van ongeveer 30 g as-vrij drooggewicht (AVDW) per m2 aangetroffen. In het begin van de 80-er jaren trad er een toename op tot ongeveer 20-35 g A VDW per m2. Tot op heden laten de biomassa en produktiviteit van het macrozoobenthos geen trendmatige achteruitgangen zien. Gedurende de jaren 1974-1993 zijn er waarnemingen verricht aan de vestiging en groei van onvolwassen platvis (schol en bot) en van garnaal op de getijdeplaten. Deze gegevens zijn gerelateerd met de trends in eutrofi\u00ebring. Er werd geen relatie gevonden tussen eutrofi\u00ebring en de grootte van de vestiging of op de groei van platvis en garnaal. De fluctuaties in aantallen lijken door andere factoren bepaald te worden dan door de voedselomstandigheden op de getijdeplaten. Op dit moment zijn er geen aanwijzingen voor een negatief effect van de afgenomen concentraties aan nutri\u00ebnten in de westelijke Waddenzee op de biomassa en produktiviteit van het macrozoobenthos en de belangrijkste epibentische predatoren op de getijde- platen. Commerci\u00eble visserij op vooral mosselzaad, de andere antropogene aktiviteit in het gebied, lijkt onder bepaalde omstandigheden wel een negatief effect te kunnen hebben op de vogelstand in de Waddenzee. In 1990 en 1991 waren er extreem geringe hoeveelheden mossels aanwezig in de Waddenzee als gevolg van een laag voortplantingssucces in de drie voorafgaande jaren (1988, 1989, 1990) in combinatie met een intensieve visserij op mosselzaad. In deze drie jaren was er eveneens een geringe voortplanting van kokkels, een andere belangrijke voedselbron voor vogels, terwijlook hierop de visserij door bleef gaan. Zowel de eidereend als de scholekster raakten hierdoor in een situatie waarin voedselgebrek voor deze soorten optrad. Een aanzienlijke hoeveelheid eidereenden verliet de Waddenzee of kwam om. Ook de sterfte van scholeksters was verhoogd in de winter 1990\/1991.","BibLvlCode":"MS","StandardTitle":"Effecten van antropogene activiteiten op de produktiviteit van het ecosysteem in de westelijke Waddenzee","OrigTitleLangCode":"nl","OrigTitleLangCodeExtended":"dut","OrigTitleLangID":41,"DateLastModified":{"date":"2025-07-21 01:33:23.796402","timezone_type":1,"timezone":"+02:00"},"UserAccessRight":null,"UserAccID":null,"AuthorKeywords":null,"OtherDescriptors":null,"Notes":null,"AnaPub":null,"MonPub":1995,"DateUpdate":"2025-07-14","DateCreate":"2000-08-24","SecASFANote":null,"ConfID":null,"PeerRev":0,"VlizCoreFlag":1,"WoScode":null,"VABBcode":null,"OpenAcc":1},"refs":null,"anarec":null,"monrec":{"MonID":603,"ISBN":null,"PubliDate":1995,"IssueDate":null,"Volume":"95","Issue":"9","Pagination":"56","Place":"Den Haag","Edition":null,"BRefXtra":null,"BRefXtraRR":null,"SerID":33963,"SerRR":"BEON Rapport = BEON-report. Programma Bureau BEON: Den Haag.  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